AD-AI02 A76 UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES DEPT 0--ETC F/73PHOTOPHYSICS AND PHOTOCHEMISTRY OF PENTACARBONYLPYRIDINO-TUNOST--ETCIU)AUG Al A J LEES. A W ADAMSON N00014-76-C-0548

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CD Potophysics and Photoche-istry of Perntacarbonyl- 'Technical Report '15, 1981pyridino-tungsten((6) Complexes Wlhich Luminesce-",

in Fluid Solution S 6. PERFORMIN - OR. REPORT NUMBER

*00 7.HA.Lgs~ahjOyM3ic, .Ai istai r O. iLees a Arthur W. Adamson 00tO0014-76-C-0548k/

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19. KEY WORDS (Cowin.,. on geverse side z! roce -eor/ and Idntlf '.. by block :u=!, r)

Tungsten EmissionCarborvi Ccioexes QuenchingGroup Six Complexes KineticsPhotochemistry SubstitutionPhoto pY ics

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See manuscript.

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TECHNICAL REPORT NO. 15

Photophysics and Photochemistry of Pentacarbonylpyridino-tungsten(O)

Complexes Which Luminesce in Fluid Solution

by

Alistair J. Lees and Arthur W. Adamson

Prepared for Publication

for

Journal of the American Chemical Society

University of Southern CaliforniaDepartment of Chemistry

Los Angeles, California 90007

Accession ForAugust 5, 1981 NTIS CRA&I

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11 . ..

Photophysics and Photcchenistry of Pentacarbonylpyridino-tungsten(O)

Complexes which Luminesce in Fluid Solution

Alistair J. Lees and Arthur W. Adamson

Department of Chemistry, University of Southern California, Los Angeles,

California 90007

Abstract

Luminescence data are reported for W(CO)5 L complexes, where L =

4-acetylpyridine, 4-benzoylpyridine, 4-cyanopyridine and 4-formylpyridine,

as solids, and in fluid solution. Photosubstitution quantum yields

(for the dissociation of L) have been recorded for these O(CO)5L

complexes in several solvents using various irradiation wavelengths.

Apparent activation energies for the W(CO) 5 L complexes in several solvents

have been measured from the temperature dependencies of the emission and

photoreactivity processes. Quenching of the emission and photoreactivity

processes are reported for several quenchers; the results are used to

bracket the energies of the emitting state for each complex. Two low-

lying metal to liganj change-transfer excited states are implicated in the

radiative decay pr3:ess. Possible excited state schemes for these

W(CO) L complexes a2e discussed in accordance with the experimental5

observations. Exc:-E State absorption and primary photoproduct spectra

have been recorde,: f:r ', ,(CO)5L complexes in methylcyclohexane and

benzene by monitur-: :-riq!.:es. A common photoproduct is inferred,

its spectrum bein; c.~e to that of W(CO) S, where S denotes solvent,

following pulse !a-e' sozolysis of 1D(CO) 6 as previously reported by us.

iI

-. .

-2-

Introduction

1-5Following initial studies by Strohmeier and coworkers the

photochemical behavior of group 6bmetal carbonyls and their derivatives6-21

has been the subject of numerous investigations. 6 lany of the early

papers were centered around the photolysis of the parent hexacarbonyls

in solution and as rigid glasses. More recently, coRventional flash

photolysis techniques heve provided information about intermediates

produced in these photolyses.2 2 2 7

Of current interest is the photochemistry of metal complexes

having low-lying metal to ligand charge-transfer (MLCT) excited states,29 41

42-59particularly substituted rononuclear metal carbonyls. Complexes

of the general formula (CO) 5L, where L is an oxygen or nitrogen donor,

have intriguing spectroscopic and photochemical characteristics. In

rigid glasses at 77 K :.ey luminesce, the emission having been assigned

to either a 3E A, ligend-field (LF) transition or a li - L charge-

51,60,61transfer (CT) transition, depending on the nature of L.5 '6

' The

electronic absorption spectra indicate that as L becomes more electron

withdrawing, the CT state lowers in energy, and for various substituted51

pyridines as L, has teen inferred to be the lowest lying state. The

- L CT state has bee- snown to be significantly less reactive than the

ic,,est L7 state for s' tsitution of L in W(CO)5 L complexes, analogous

2+ 29-34to previous findings fsr Ru(, H3 )5L complexes. Therefore, in

the cases of 1(CO) c:-plexes where a W - L CT absorption is the lowest

enercy absorption, the ;hotosubstitution quantum yield of L in W(CO)5L

is relatively low. Correspondingly, the luminescence from W(CO)5L cor-plexes

4n 7PA at 77 K was -r to shift to lower energy maxima and to show

an i.crease in emissi li2feti..e with increasing electron-withdrawing

-3-

effect of L. This was the case for 14(CO)5L complexes where L5i

4-ACpyr (4-acetylpyridine), 4-BNpyr (4-benzoylpyridine), 4-CNpyr

(4-cyanopyridine) and 4-FMpyr (4-formylpyridine).51

V.(CO) 5L complexes were not thought to luminesce in room temperature

solutions, presumably because of rapid ligand dissociation and non-

radiative decay to the ground state. However, recently we have

observed emission from W(CO)5(4-CNpyr) in room temperature solution and

62the quenching of emission and photosubstitution reactivity by anthracene.

As a consequence, a complete study of the photochemistry and photophysics

of W(CO)5L complexes has been undertaken, the results of which are

reported here.

Results

Synthesis of W(CO)5L. W(CO)5L complexes were prepared either directly

(reactionl)) or via the tetrahydrofuran complex, W(CO)5(THF), (reactions

(2) - (3)) according to a literature procedure.5'9

hc W(CO)5L + CO (1)W(CO)6 L

Ar purgedmethylcyclohexane

W(Co)6 urged W(CO) 5(THF) + CO (2)

THF

W(CO)5(THF) . W(CO) 5 L + THF (3)

-4-

Reaction (1) was used to prepare W(CO) 5L, where L : pyridine, piperidine,

diethylethyla-,ire, triethylamine, 2,4,6-trimethylpyridine, 2-acetylpyridine,

4-acetylpyridire, 2-benzoylpyridine, 4-benzoylpyridine, 4-cyanopyridine,

4-formylpyridine, acetone, diethylether, ethanol, and l-pentene. A

major limitation of this procedure, however, is that during production

of W(CO) 5L seccndary photochemical reactions can take place which may

lead to other suhstituted products. The route involving prior photogeneration

of the tetra yrofuran complex, W(CO) 5(THF) (reactions (2)-(3)), has considerable

precedence, as it largely avoids secondary photolysis products. Reactions

(2) - (3) were used to prepare W(CO)5L, where L = pyridine, piperidine,

4-acetylpyridine, 4-benzoylpyridine, 4-cyanopyridine and 4-formylpyridine,

and the prodicts were isolated as solid complexes.

Electrcnic Atsorption Spectra. Absorption spectra in the 300 - 600

nm region for ;iCO),(4-ACpyr), W(CO) 5(4-BNpyr), l(CO) 5(4-CNpyr) ,

O(C)5 ( -F.y and W:(CO) 6 in methylcyclohexane are shown in Figure la.

A comparison of the absorption spectra of W(CO) 5(4-CNpyr) in methylcyclo-

hexane and i:1 (by volume) methylcyclohexane/benzene is illustrated in

Figure lb. A.sorption spectral data for the complexes studied are

...arize_ ir I

Lu~i~e~~ :re Data. Corrected emission spectra for W(CO)5 (4-ACpyr),

r". iy0) and W(CO)4-Ftipyr), as solids, and in

rethylcyc1 c.'exae and benzene at 298 K are shown in Figure 2. The band

axima ard l1,.-irescence quantum yields are summarized in Table II. The

e-lission s:.zncra at 298 K were found to be independent of excitation wavelength;

.e em.is~ij fr-~ uCO)5 (4-Cpyr ) was also determined in methylcyclohexane

ILIA - -

-5-

WL

using 530 nm excitation from the Nd glass laser and was the same within

experimental error to that shown in Figure 2. For W(CO) 5(4-Cf~pyr) in a

methylcyclohexane glass at 77 K the emission spectrum and emission

lifetime recorded following 353 nm excitation was as reported previously.51

Emission was not observed from the glass using 530 nm excitation.

Very weak emissions were observed in the 500 - 600 nm region following

pulsed excitation at 353 nm of 5xlO -5 - 2xlO -4 M solutions of W(CO)5L in

methylcyclohexane at 298 K, where L is pyridine, piperidine, diethyl-

methylamine, triethylamine, 2,4,6-trimethylpyridine, 2-acetylpyridine,

2-benzoylpyridine, acetone, diethylether, ethanol, and 1-pentene.

The emissions from these solutions followed the Nd laser pulse, that is,

the lifetimes were less than 10 ns.

The relative emission intensity of 5.5xlO' 5M W(CO)5(4-ACpyr) in

methylcyclohexane as a function of temperature was measured using 353 nm

excitation. The relative emission intensities at 278, 283, 288,-293, 298 -

and 303 K are 5.9, 6.3, 7.1, 7.4, 7.7 and 8.5 respectively; the least

squares line, In I = A exp (-E*/RT), corresponds to an apparent activation

energy of 2.4 ± 1 kcal 7oI-I

Emission lifeti-es () recorded from W(CO)5(4-ACpyr), W(CO)5(4-BNpyr),

W(CO) 5(4-CNpyr) and '4i',O).4-FMpyr) as solids or in solution as a function

of temperature are r-:-rtel, in Table III. Emission lifetimes were

observed to he t'ne s--_ 'olo,..,inq either 353 nm or 530 nm excitation.

Plots of In lI/T vers.-S 117 give good Arrhenius behavior for the solid

complexes and the sol : studied, the least-squares line being 1/h[

A exp (-E*/RT), R in apparent activation energies (E*) and

frequency factors .r sown in Table IV. The activation energies

are estimated t - I kcal rol

. . .. .. ... ,, al4mo

-6-

The luminescence of 1.4xlO - 2 M benzophenone and 2.5xi0 "I M biacetyl

was quenched by 2 - 5xlO- 5 (CO)5 (4-ACpyr), W'(CO) 5 (4-BNpyr), II(CO) 5 (4-C4,pyr)

and ;l(CO) 5 (FfIpyr) complexes in solution. Emission spectra at 293 K were

recorded from solutions of(a) 1.4xlO - N benzophenone in benzene and

-2 -5,t) 1.4xlO -2 benzophenone with 4.9xi0 - M II(CO) 5 (4-ACpyr) in benzene

using 353 nm excitation. At these solution concentrations, excitation at

353 r.i can be assumed to be entirely into benzophenone. The intensity of

the eimission spectrum obtained from(a) is 3.2 times that obtained from

,-,, correcting the latter spectrum for the inner filter absorption by

the ;(CO) 5 (4-ACpyr) complex. Emission lifetimes of the benzophenone

e.ission were recorded from these solutions using 353 nm excitation and

were found to be (a)8 .s and (b) 2.5 is respectively. Using the Stern-

Volrer equation: -i°/T 1 + k -r [Q], where t° is the lifetime in theq

absence of quencher, r is the lifetime with quencher present, and [Q] is

.. . the quencher concentration, the bimolecular quenching rate constant kq

is calculated to be 5.6xi0 9 M-s - .

Emissions from 5-8IlO- 5 M solutions of W(CO) 5(4-ACpyr), W(CO)5(4-BNpyr),

"2;5 (4-CNpyr) and II(CO) 5 (4-FMpyr) in methylcyclohexane were quenched

by the presence of 5xlO 3 M1 anthracene, 9-methylanthracene and

1,2-:enzanthracene. Emission from 5-8xlO-51 solutions of W(CO)5(4-ACpyr),

,;' :';(4-BKpyr), Il.(CO) 5 (4-CNpyr) and W(CO) 5 (4-Fpyr) in benzene was

-3edby the presence of 5xlO M acenapthaquinone. Emission quenching

.as not observed from solutions of 5-xlO 5M W(CO)5(4-ACpyr),

~',?)-]5(4-BNpyr), W(CO) 5(4-CNpyr) and W(CO) 5(4-FMpyr) containing 5x1O3 M

c-r,sere, coronene, benzil, fluoranthene and 1,2,5,6-dibenzan..

:--.acene. The quenching of the emission lifetime of W(CO) 5(4-CNr~yr)

a nithracene follows Sterr,-Volmer kinetics and is shown in Figure 3. The

sl ;e k q corresponds to a bimolecular quenching rate constant of• ] 1-l -l.'

.j NS

-Ll : . . . .. .1 il I .. I '''' i., -

-7-

Photosubstitution -eactivity. Figure 4 illustrates the spectral

sequence accompanying t - '57 nm irradiation of a) W(CO) 5(4-ACpyr) in

methylcyclohexane and b) >WCO)5 (4-BMpyr) in methylcyclohexane, showing

progression to near zero terA.inal absorbance in the 450 - 500 nm region.

Before photolysis 0.05 ! ethanol was added to each solution; the product

in each case is W(CO) '2 5""H) apparently uncomplicated by side or subsequent

reactions. Quantum yields f:) for this photosubstitution reaction have

been measured for U(CO 5,- opyr) as a function of solvent and temperature

and are reported in Table ,. Plots of ln versus I/T for W(CO) 5(4-CNpyr)

solutions show goo rrhenius behavior, the least-squares lines

corresponding to apparent activation energies of 7.9 ± 1 kcal mol-1

(methylcyclohexane), 7.S 1 I kcal mol-l (iso-octane) and 7.6 ± 1 kcal mol -

(benzene). The temperat.re e:endencies of quantum yields for W(CO)5(4-ACpyr)

and W'(0) 5 (4-2,pyr' - .. .ohexan containing 0.05 M ethanol are

reported in Table VI. Te data for W(CO) 5( 4-ACpyr) and W(CO) 5(4-BNpyr)

showed good Arrhenius be a,',or, corresponding to apparent activation

energies of 7.9 ± 1 kcal 7 1' and 7.5 1 1 kcal mol' l respectively. An

early loss of isosbestic :i'zs was observed on photolysis of W(CO) 5L

solutions not containi-: a 'east 0.325 M entering ligand. It was

noted that ther: ',as a 4: n depedence of both the photosubstitution

quantum yield and e-is -:-::'-.e on the ethanol concentration in

the 3.025 - 0.1 , rar.e; :::i-; :~at ethanol is not a quencher in

dilute solution and Z: _-. ":e :c-p"etely the photochemically produced

w'(C0) 5 intermediate. :--,eld data were not obtained for.

W(CO) 5(4-FMpyr) in te..:.i:e ne Lecause of thermal reaction.

The photosu ti.-ffi:- -a:-ivity of 5.5xlO- 5M W(CO)5 (4-CNpyr)

in methylcyclohexae : . . ethanol was recorded at two other

-i4

irradiation wavelengths, -:33 r-1 and 520 nrn. At the 520 nm

irratiation wavelength, the_ yield is temperature dependent, the values

at 283, 283, 293, 290 and 3 _3 K are 0.011, 0.013, 0.016, 0.021 and 0.026

respectively. These data show good Arrhenius behavior, the least-squares

lin corePonding to an apparent activation energy of 7.6 ± 1 1cl.ol-

At the 4"30 rn irradiation ..aVelength, the yield is temperature dependent,

the values at 233, 233, 213, 293 and 303 K are 0.095, 0.099, 0.110,

0.120 and 0.133 respectively. The least-squares line of an Arrhenius

type plot cclrrespords to .;n apparent activation energy of 3.2 ± 1 kcal Mar1.

Quenching of the protosub;stitution reactivity of 1W(CO) 5(4-Ctlpyr)

with anth'racene eas observ.ed using 520 nm irradiation wavelength, near

that used in recording t'" e lifetime quenching data. A Stern-Volmer

type plot ofil /: where superscript zero denotes absence of que .ncher,

is linear against anth.racere concentration (see Figure 3). The slope

is comon with the lifetiFre data, within experimental error, corresponding

9 -lI -l1to a bi-olecular rate constant of 4.OxlO M s about the diffusion

controlled liinit.

Quen: -i r of the pI-otosutstitution reactivity of W(CO) 5 (4-Ctlpyr)

with anthracene was -=lso 3tbServed using 430 nm irradiation wavelength.

Quantu7 yields were recorded o,.'er the first 5'; of reaction; this largely

avoids a zjiid-up of the_ :r::c.oprcduct W(CO) 5(OEt) which absorbs at this

Aaveen:. e-E: n -- no obey Stern-Volimer kinetics

(see Fi:ure 3).

Excied tate~:'t~: ard Primary Photo product Spectra.. Following

353r-.puse x~tat:r;-E.. 5M (C)4-ACpyr), W(CO) (4-BNpyr) and

WC)5ir,~t.2:hxn and benzene the transmitted

Foioi::e!- 4..eda rst-antaneous deflection from V 0to Vi'that

~-8-

irradiation wavelengths, 1-3 r and 520 nm. At the 520 nm

irra-iation wavelength, the yield is temperature dependent, the values

at 233, 223, 293, 293 and 3'3 K are 0.011, 0.013, 0.016, 0.021 and 0.026

respectively. These data s;ow good Arrhenius behavior, the least-squares-I

line corresponding to an apparent activation energy of 7.6 t 1 kcal mol

At the "30 rn irradiation ..avelength, the yield is temperature dependent,

the values at 233, 20, 23, 293 and 303 K are 0.095, 0.099, 0.110,

0.120 and 0.133 respectively. The least-squares line of an Arrhenius

type plo: ccrresponds to an apparent activation energy of 3.2 ± 1 kcal Mol1 l.

Quenching of the ph.otosjbstitution reactivity of W(CO)5 (4-Clpyr)

with ant;-,racene was observed using 520 nm irradiation wavelength, near

that used in recording te lifetime quenching data. A Stern-Volmer

type plot of :°/:, where superscript zero denotes absence of quencher,

is linear against ant ,racene concentration (see Figure 3). The slope

is com -on with the lifetire data, within experimental error, corresponding

to a birolecular rate constant of 4.OxlO 9 M s I , about the diffusion

controlled liit.

Quer,:-ir g of the p otcsutstitution reactivity of W(CO) 5 (4-Ctlpyr)

with anthrace.e was a!so obs-red using 430 nm irradiation wavelength.

Quantu7 yields were recored over the first 5c of reaction; this largely

avoids a ziid-up of the r (CO) 5 (OEt) which absorbs at this

:ave- n ....T;- -", ' not obey Stern-Volier kinetics

(see Figre 3).

Excite1 Sa:"--:-ti ;:-ad rPrmary Photoproduct Spectra. Following

353 r7. pjise :ita . . 5-.' . W(CO) 5(4-ACpyr), W(CO)5 (4-UNpyr) end

W(CO)(--',yr in -t-:. o hxane and benzene the transmitted

,-onitcri-: -ea- s 3zed a- irstantaneous deflection from V to Vin, that0 in'

-9-

is, either an increase or decrease which followed the 20 ns laser pulse.

Here, V denotes voltage a- the oscilloscope signal from the photo-

multiplier. A measurably, slow change then occurred, in which Vt, the

intensity at time t after the pulse, either increased or decreased to

a final value V. The irstantaneous and relatively slow deflections are

assigned to excited state atsorption (ESA) and the formation of primary

photoproduct (PP) respec-ively. The extinction coefficients of the

excited state absorptic ard the primary photoproduct were calculated

using equations (4) an- -

logl VoVin+ 0.9 DO10910 "Vo"in + 0

ESA o.; C (4)0

logl ''0/. + 0.9 DCPP : C.; (5)

C0 is the concentration of the complex, and D is the optical density

at the monitoring wavelength. Equations (4) and (5) correct for the

monitoring geometry (see -x.:erimental). The actual degree of photolysis

by a single laser pulse was essentially l00' in the monitoring volume.

The calculated ex:-c7: state absorption spectra for W(CO)5(4-ACpyr),

(CO)5 (4-0..pyr) and .->-CNpyr) in methylcyclohexane and benzene

are shown in Figu.-e - ecay of the excited state absorption for

any of the W(CO)5L cc- wes 'as observed to be a single exponential, equal

within experimental arr-: :o the emission lifetime reported in Table III.

The absorption spectra - t p primary photoproducts following excitation

of W(CO)5(4-ACpyr). W"'^C z- 'pyr) and W(CO) 5(4-G!pyr) in metylcyclo-

hexane and benzene are in Figure 6.

-10-

Discussion

Electronic ~s':i~Snectra. The absorption spectra shown in

Figure 1 show two disti7:t absorption maxima (both with :- 5X10 M 1 cm- I

for each of the W(C')- ccr-plexes in methylcyclohexane. The higher

energjy absorption tart *-axi-a at 403 nm (± 2 nm) are essentially

unshifted by variations in the nature of the substituent on the pyridine

ligand and the solVEr:. -e~iu7 (see Figure I and Table 1). The lower

energy absorption -axi-a are observed in the range 435 - 470 nm

and their positionsiljs--rate an extraordinary dependence on the nature

of ligand substituert art the solvent medium (see Figure 1 and Table 1).

As the nature of the pyridine ligand substituent becomes more electron

withdrawing, that is, as one moves from L =4-ACpyr to L = 4-FMpyr, the

band undergoes a red- sh'ift. In a more polar solvent medium the band

apPears to reduce in jtrivand to blue shift; for the solvents

benzene, tetrahydro f;rar ar-d ethanol, this band progressively overlaps

with the high energye tra-si:ion and their maxima becomes indistinguishable

(see Table I). These atsorption Lands at -,403 nm and 435 - 470 nm have been

previously assigne:- --- a 'j-~an.'-field (LF) IA I(e 4b 2 )-- E(e 3b2 2a,1

transition and a re~al - ligan d c',arge-transfer (rILCI) transition

51respectively. C r :-=: :his assignment.

'.Zeaker absor:-t: ::szrved in the W(CO) 5L spectra shown in

Fi;ure 1. The ma- ar'j s~ouldersat -- 370 nnm do riot shift

appreciably with '-, :: :yiidine ligand substituent and the

solvent polarity. .e ~Lands are assigned as ligand-field

transitions. 71'e 1:. - , .t-rs to the 435 - 470 nm bands are

sensitive to ch ~~:~' ~ligand substituent and solvent

polarity. This ai-: '.: J 520 nm range, is therefore

again assigned as a -,o ~adc'arge-transfer transition. The

-11-

use of spin multiplicity designations has been avoided in these assignments

because there is expected to be substantial coupling of spin and orbital

angular moments for such heavy transition metal complexes.

The energy of an excited state formed immediately following the

absorption process can be approximated from the long wavelength tail

of a broad-band absorption. We have assumed the absorpition bands in"0-0

the W(CO) 5L spectrum t) be gaussian in shape, and have taken the

transition to be at where absorption intensity at = (0.05)

(cbsorpticn intensity at ,max ) . From the electronic spectra of the

W(CO) 5 L complexes, where L is 4-ACpyr, 4-Bflpyr, 4-CNpyr and 4-FMpyr in

methylcyclohexane, iso-octane and benzene the positions of the LF

transition V5v are estir-ated to be 22.6 t 0.4 kK. From these electronic

spectra the positiorns of the MLCT transitions are estimated to be at

19.5 ± 0.4 kK and 18.5 = 0.4 kK.

Luminescence Data. Luminescence with quantum yields of the order

of 10 - 4 - lO 3 was observed from .(CO) 5 L complexes, where L is 4-ACpyr,

4-Blpyr, 4-CNpyr and 4-FMpyr following excitation in fluid solution

(see Figure 2 and Table II). These results are the first of their kind

obtained from group 6b metal carbonyl complexes. Very weak emissions

with decays which were immeasurable on our apparatus were observed

from other U(CO)5L co-plexes in fluid solution, where L is pyridine,

i~eridine, 'diet.ylr-etylamine, triethylamine, 2 , 4 ,6-trimethypyridine,

2-acetylpyridine, 2-berzoylpyridine, acetone, diethylether, ethanol and

l-pentene. The more electron-withdrawing substituents give rise to

c ..er energy IMT e>°ited states; when the ligand substituent is the

acetyl, benzoyl, cyano or formyl groups and in the para position on

the pyridine, the ILC:- Excited states move below the LF excited state.

-12-

The W(CO) 5 L complexes which have MLCT excited states as the lowest

energy absorption features (see Figure 1, Table I and reference 51) exhibit

measurable luminescence and relatively long radiative decays in fluid

complexes in EPA glasses.51

Solvent effects for the W(CO)5L luminescence are also noticeable.

For the non-polar solvents studied, the emissions were generally of

greater yield and with longer lifetime compared to the more polar

solvents. For the W(CO/5L complexes in tetrahydrofuran and ethanol,

the luminescence was very weak and the emission lifetimes were relatively

short. These effects are attributed to an increased rate of nonradiative

decay from the excited state of W(CO)5L in the more polar solvents. As

a result of thermal substitution reactions of the W(CO)5L complexes in

tetrahydrofuran and ethanol, lifetime data were not obtained for temperatures

above 283 K.

The pattern for our !(CO) 5 L series is that if the MLCT absorptions

lie below the first ligand field absorption, emission of relatively

long lifetime is observe . As a caution against generalization, the

complex W(CO) 5(benzoz]cinnoline) showed no detectable emission, yet has a

55MLCT absorption at 533 r- in n-hexane solvent, or well below the energy

of such absorptions in Our series. The benzo[clcinnoline ligand

is pes y co ir:~ ~ou-55is presumabtly coorjr_ :t'rough one of the nitrogen atoms.

m~m,

-13-

It is r::- clear why this cc'-plex behaves differently from those of

our series,*~u it r'ay te rel evant that the 538 nm MLCT band does not

show a lcng wavelength s -oulder, while our series of complexes do.

The en'ergy of an e-itting state can be approximated from the short

wavelen::h - tail of the Er-ission spectrum. We have assumed the emission

band frc- a -C0) 5L co-Plex to be gaussian, and have taken the

VO0transition to be .. ,,where emission intensity at \)5% =(0.05)

Omission intensity at.) The positions of the emitting state

for the W'.C)L complexes, where L is 4-ACpyr, 4-BNpyr, 4-CNpyr and

4-F'pyr in lethylcyclo -exane and benzene were thus estimated from the

emission s~ectra of Figzre 2 to be 19.6 ± 0.4 kK in each case. This value

is e;.al r;ithin experi-En--ai error to the Z) of the higher energy ?1LCT0-0

absorption; the emiission. is therefore assigned to this transition for

eachof he C0) co-plexes. The PUiCT excited state which was estimated

to hav'e -an energy of 12.5 0.4 kK has too low an energy to be the

eniittin; state.

Th e lu-iinescence dat'a that was obtained from the WJ(C0) 5L complexes

in so1*jti~n -Aas observed to be the same follo-wing either 353 nm or 530 n,-,

excitat-,:-. :ilses. Te .:A-se energy of 530 nm excitation corresponds

to 13. ,: toDj low to :.:''iate the M1LCT excited state at 19.6 ± 0.4 kK.

It is n-dthat t~ca energy is required from the solution to

p3;ulate "is stlate. 'o.erat glass temperatures very little energy

wiE Lzaiz to t-eexcited tW(CO) 5 L molecule from its environment

and eitorat 53] n- should not produce the emitting state. This we

61~~ e experi-e-to, W(C0) 5(4-CfJpyr) in a methylcyclohexane

glass a-: 77 was ctser-ve to luminesce following 353 nm excitation,

but r: !_;-i eSCEs Ce ,ES r-served following 530 nm excitation. This is

further e'.-Idsnce tftat it_ is the higher-energy MLCT excited state that is

the e-i-_t~r state.

-14-

The apparent activation energy for the emission intensity of

W(CO)5(4-ACpyr) in methylcyclohexane is 2.4 ± 1 kcal mol -l, and equal to

the mean of the apparent activation energies obtained from the temperature

dependence of the emission lifetimes for the W(CO)5L complexes in solution

5K(Table IV). This activation energy, within experimental error, corresponds

to the energy differences assigned between the low-lying MLCT excited

states. Furthern.ore, the emission intensity increases and the emission

lifetime decreases as the solution temperature is raised, behavior which

is uncharacteristic of a single emitting state. These results imply

that the higher-energy MLCT excited state (the emitting one) is thermally

populated by the lower-energy MLCT excited state for the W(CO)5 L complexes

which luminesce in fluid solution.

Quenching experiments were undertaken to bracket the energies of

the excited states of W(CO)5L, where L is 4-ACpyr, 4-BNpyr, 4-CNpyr and

4-Ftipyr. These W(CO) 5L complexes were observed to act as quenchers at

approximately diffusion controlled rates for the phosphorescence of

benzophenone -r- biace:yl. The triplet energies (ET) for

benzophencre ard iacetyl are 24.0 kK and 19.2 kK respectively.6 3

Assuming t.at the quenching process is energy transfer, this places the

energy of the quenching excited state of W(CO) 5L as < 19.2 kK. The

W(CO)5L e-ission was also quenched by several anthracenes, which strongly

suggests zt erer::, transfer is the quenching mechanism. W(CO)5L

64emissions were :uerzhed bf anthracene (ET = 14.7 kK), 9-methylanthracene

(ET = 16.2 kK), " 1,2-tenzanthracene (ET-. 16.5 kK)6 4 and acenaphthaquinone

(ET = 17.9 'kK) t t nct 5y 1,2,5,6-dibenzanthracene (ET =18.3 kK),6 4

fluo=ant-.-ee, 6 4 benzil (E = 18.8 kK), 6 3

fluoranthe1 1 1 6',, (ET coronne (ET

191 K) o :.rse T (E 20.0 k). 6 These results bracket the energy

-15-

of the quenchable excited state of W(CO) 5 L to be 17.9 - 18.3 kK. The

-data imply that it is only the lower-energy MLCT excited state (18.5 _ 0.4 kK)

which is involved in the energy transfer mechanism.

The quenching of the emission lifetime of W(CO)5 (4-Clpyr) follows

Stern-Volmer kinetics (Figure 3) with a bimolecular quenching rate

constant approaching that of the diffusion controlled limit.

Photosubstitutio, Peactivity. Photodissociation of ligand (L) has

been shown to be the -ost efficient chemical process over our excitation

region (equation v' 15,51,57

hW5 L 2 W(CO) 5(C 2 H5OH) (6)

In the presence of an excess of entering ligand eg. 0.025 - 0.1 M ethanol,

the photosubstitution reaction appears to be uncomplicated by side or

subsequent reactions. Figure 4 illustrates the spectral sequence

acco-parying the 1S5 r.. photolyses of :,4(CO) 5 L complexes, showing a clear

progression to near zero terminal absorbance in the 450 - 500 nm region.

The quantum yields, :, deternined for the reaction (6) are listed in

Table V. The low values are consistent with results reported for

substituted pyridi-e a:5nds of this type; 51 this seems to be characteristic

of the case where - 'T state lies telow the LF state. Quantum yields

for comiolexes in .. i --e LF state is lowest in energy are significantly51

higher.

The quantu- yief K-- '.:(CO)5 (4-Ctlpyr) undergoing reaction (6), does not

show a solvent dec z- :. In t2trahydrofuran and ethanol, the quantum

yields for W(CO)- -,:. .ere measured at 283 K only since thermal

substitution reacti:,s 4'ere taking place at higher temperatures. The

-16- .- - -

lack of dependence of the quantum yield on ethanol concentration is a

good indication that ethanol is not a quencher in solution, and does

scavenge completely the photochemically produced W(CO)5 intermediate.5I

The quantum yield for W(CO)5(4-CNpyr) is temperature dependent.

The apparent activation energies for the photosubstitution quantum yields

at 465 nm of W(CO) 5(4-C~pyr) in methylcyclohexane, iso-octane and benzene

are the same within experimental error, with a mean value of 7.8 ± 1 kcal

mol 1. Quantum yields for W(CO)5(4-ACpyr) and W(CO) 5(4-BNpyr) were lower

than the above ones at any given temperature (see Table VI), the data

corresponding to apparent activation energies of 7.9 ± 1 kcal mol -1 and

7.5 ± I kcal mol respectively. These activation energies correspond,

within experimental error, to the energy difference between the higher

energy MLCT state (19.5 z 0.4 kK) and the LF state (22.6 ± 0.4 kK); the

implication is that chemical reaction occurs from the higher lying LF

state, which is in steady-state equilibrium with the emitting CT state.

The quantum yield for A(C0)5(4-CNpyr) in methylcyclohexane is dependent

on the irradiation wavelength, being larger following higher energy

excitation. The apparent activation energy following 520 nm photolysis

(7.6 ± 1 kcal mol l ) is the same within experimental error to that observed

for the 465 nn photoly.sis r.9 ± 1 kcal mol- ), whereas the apparent activation

energy following 430 r:7 photolysis (3.2 , 1 kcal mol I) is significantly

lower. We attribute toese observations to direct population of the LF

excited state folloe~ing I0 nin excitation,which gives rise to substitu-

tion at a competitive ra:e to internal conversion to the relatively

unreactive low-lying "LCT states.

The quenching of t-e 7hotosubstitution quantum yield of W(CO) 5 (4-Ctlpyr)

by anthracene at 520 nn follows Stern-Volmer kinetics, with a common slope

within experimental err:r to that observed for the emission lifetime

-17-

quenching (Figure 3). This result strongly indicates that the emitting

state of W(CO)5(4-C{pyr) is implicated in the photochemistry. Quantum

yield quenching reasure-ents are also recorded using 430 nm excitation.

The data does not obey Stern-Volmer kinetics (see Figure 3).

The non-linear behavior is further evidence of direct population of the

LF excited state following 430 nm excitation which chemically reacts at

a competitive rate to internal conversion to the quenchable low-lying

MLCT states.

Whereas the photoreactivity (f) quenching data for W(CO) 5(4-CNpyr)

in methylcyclohexane is dependent on the excitation wavelength, the

emission lifetime (-) quenching data can be assumed to obey the measured

Stern-Volmer type kinetics at any excitation wavelength. The extent

of unquenchable photolysis at 430 nm of W(CO) 5(4-CNpyr) in methylcyclo-

hexane is obtainable from a plot of / O versus T/T° 66 as shown in

Figure 7. The intercept gives the unquenchable yield, 33% in this case.

We attribute this yield to direct chemical reaction through the LF

excited state following 430 nm excitation of W(CO)5(4-CNpyr) in methyl-

cyclohexane.

Excited State .!bscr~tion and Primary Photoproduct Spectra. The

excited state absorption (ESA) spectra for W(CO)5(4-ACpyr), W(CO)5(4-Mipyr)

and W(CO)5.-'%pyr) in 7etylcyclohexane and benzene show two absorptions

(Figure :. The ats:r:.:ions decay with the lifetime of the emitting

state. We therefore assign the ESA absorption features to be due to

transitions fro-, the i' er-energy MLCT state to high energy excited

states.

The absorption spectr! of the primary photoproducts of W(CO)5 (4-ACpyr),W(C)5(-9'pyr a-d pyr,,

W(CO)5 '~-2pyr) and WC; f-, -C'Ipyr) following laser pulse photolysis

are coincident within ei:=ri -ental error in methylcyclohexane (Amax z 428 nm)

I°T

aad benzene .42 !7-) see Figure 6). For the W(CO) L complexes

I - -I1r, -ethylcyclohexane, f. o x is 6.7xlf a M cm , and the

position of the maxi7um is within the range of wavelengths reported for

tungsten pentacarbonyf s:ecies generated in low temperature SF6 (461 nm),

Ar (437 nm), Xe (417 r--- 4 (413 nm) matrices, 13 as well as in the

pulsed radiolysis stud'-, ir cyclohexane (415 nm). 67 Recently, we have

shon that the inter'-e:ia-e produced in the laser pulse photolysis of

w(CO)6 in methylcyclcevXa.e at room temperature is a solvent coordinated

species, W(CO)5S, wic. is then scavenged by the entering ligand,27 The

absorption spectrum of : is intermediate is the same within experimental

error as that sho.n 'ere, ,hichi-plies that the common primary photo-

.ro . .ct of the is the W(CO)5S species.,r . c of th :.(C - __ .5 .

Su'mary

Our results have t..,, t-ht the emitting state of the W(CO)5L-

co'.plexes is implicate-' i- o-potochemistry, that is, chemical reaction

occurs from or via tisst--to. Two low-lying MLCT excited states are

inferred, the emittir: :- e . -- 0.4 kK, and one which is quenchable

at !?.5 - 0.4 kK. A L:' e--itet state at 22.6 ± 0.4 kK has been estimated

fro-. the electronic. -_ . i o-ect-a, Possible excited state schemes

for the ,.(CO)5L zc-: . _-i,- ece in fluid solution are shown

in Fi.re 3.

Scheme (a) L=c ,-_-.- :e to be the lowest-lying MLCT state.

The DhotochEnical r.:- :- ::-.-- , occurs by dissociation of the U-L

..... o form a - .::-rediate, which is then scavenged by the

entering ligand. -- - . reaction must then be activated

t- e extent of

i , 4A

L _ i

-1 9-

Sche -e :b, Presert:s -P,, attractive alternative, in which chemical

reaction occurs fron. t-e LF state lying above the low-lying MLCT states,

and in steady-state eqquiliitrium with them. The observed activation[energy for zt-e p -otosutstitution reaction is now attributed primarily

to the enercy dilfference b'etw,,een the LF and MLCT states. In this scheme,

excitation leads, throu?: t -e intersystem crossing, to a MLCT state.

This state is e 7ittinS bt not highly chemically reactive. The higher

energy. L F state does raeact efficiently, but the overall quantum yield is

srall becauise of the cc-;etit'ion with non-radiative decay at the MLCT state.

The detailed, kinetics focr such a system have been reported elsewhere. 68-70

At higher excitation energies, the LF state is directly populated, and

as a conse;,uence, the :.jantum yields for photosubstituion are increased.

Similarly, at higher excitation energy the W(CO) 5L photosubstitution

shows a sicnificantlv. lo^- Le'-perature dependence and the quenching

data do not obey S tern-Vol,7er kinetics. This type of scheme (b) has been

proposed to explain the p otochemical behavior of Ru(NH 3)5 L 2 complexes 33

as well as for the present type of carbonyl complexes. 56 ,71 It has the

appealing feature of acccurnting for the increase in the quantum yield for

photosubstitution for C)Lcomplexes, where L is such that the MLCT

absorption tands are at"ige energy than the LF one.

Experi- ertar-j

Materials. - u::- -%xacarbonyl (Strem Chemicals) was purified

by sjbli-ati;-. The .E :: :jridine, piperidine, diethylmethylamine,

trietYa-re, prine, acetone, diethylether and

ethanor', are c:eca' a.'A"able and were distilled prior to use. The

ligands -; ee ri. -. ic), 2-acetylpyridine, -ctlyiie

2-be~c.li.Ve,4-.ze-:sc2 pyridine, 4-cyanopyridine and 4-formylpyridine

-20-

(Aldrich) were used w.i*t-cut further purification. Chemicals used in

qjenchinq experiments ..--re obtained from Aldrich and purified as follows:

anthracene (recrystallized from benzene), acenapthaquinone (recrystallized

from ethanol), l,2-benrze-.thracene (resublimed), benzil (resublimed),

benzophenone (recrys .al'ized five times from ethanol), biacetyl (distilled

twice), 1,2,5,6-dibernzar'thracene (recrystallized from benzene), and

9-iethylanthracene Irezrystallized from benzene); coronene, chrysene

and fluoranthene w.ere se without further purification. Solvents used

were obtained frc-. "3 .nufacturing Chemists and were OmniSolv grade.

.he methylcyclohexa e. "e-rahydrofuran .(THF) and ethanol however, were

further purified by se,eral distillations, so as to remove emitting

impurities. Alumina ',.23 Manufacturing Chemists) and silica gel

(Matheson, Coleman and eil) were used as chromatographic sorbents.

Synthesis of "'C""-L - W(CO)5L complexes were prepared in solution5-4

by 313 nm photolysis c,' 4M W(CO) 6 and 0.1 M L in argon purged

retnylcyclohexane (reaz--icn (1)). W(CO)5L complexes were prepared and

isolated by reactir g - ..ole of photoproduced W(CO)5(THF) with 4 mmol

L in argon purge. T re-tctions (2)-(3)). The THF was removed

by rotary eva.orati r and the solid product was redissolved

in iso-octane and r~fed by column chromatography on alumina or silica

-ea. The rain i-ur4--_ were founI -o be unreacted W(CO)6 and L.

-_Jution 'irst ,-- ------ ur. til the UV absorption features of

10,10) 6 could no 13r -z .ett in the eluant, followed by elution

of t.e product c:-" - ocizere rtoluene. The product was recovered

zy rotary eva2crat i:- ; . - -- uified by recrystallization. The51

ir.frared and uv-vis: "-:':'o' slectra agreed well with those published.

Cnro-atographic a .... •. .. cn ents, crystallization solvents

ard elemental analyses are given below.

W:1',..Yvridine): alu.-ira, benzene, iso-octane/benzene.

Found: C, 30.1%; H, 1.4"; N, 3.3%.

Calculated: C, 29.8'; H, 1.3%; N, 3.5'%.

WCO) (piperidine): al-a benzene, iso-octar;e/benzene.

Found: C, 29.07'; H, 2.7 ':; N, 3.7%

Calculated: C, 29.4 i; H, 2.7%; N, 3.4%.

W(Co)5 (4-acetylpyridine): alumina, benzene, n-hexane/benzene.

Found: C, 32.9:%; H, l.%; , 3.3%.

Calculated: C, 32.4.; , 1.6; N, 3.1%

W(CG)5 (-4-benzoylpyridine' : alumina, benzene, n-hexane/benzene.

Found: C, 41.0%; H, 1..-, N, 2.8%.

Calculated: C, 40.3%; -, 1.8 ; N, 2.8%;.

W(C)k4-cyanopyridire: ai]unina, benzene, iso-octane/toluene.

Fourd: C, 30.3 ; H, 1 .T'; N , 6.8%.

Calculated: C, 30.C; , 3.9%; N, 6.5".

W(CO)5(I-formylpyridire): silica gel, benzerne/iso-octane (1:2), iso-

octane/benzene.

Fc-jrd: C, 30.0:'; H, I.I%; , 3.5).

C- Icjate" : C, 30.7::; H, I .2% ; , 3.3:*-.

2.it Prcejures

.etails of the lase- .-otolysis and nonitoring equipment are

E'_-sri.-ed elsewhere. E7.ission lifetires were recorded using either

frercy dubled (53^ .r tripled (353 n) 20-ns pulses from the Id

class laser and considere- to be accurate to l I0:'. Emission was recorded

at any sin~le waveler:- ')" 650 n region) by a Jarrell-Ash Mark 10

a. ay sigle avel r_-= ,r , - 6 0 n

-22-

mcrccrcmator and detected by an RCA 7265 photomultiplier and Tektronix

Y :ei 7544 oscilloscope. Corning glass filters were placed on the mono-

chro-.ator entrance slit :o block out the laser light but transmit at

greater than 580 nm. Plcts of log (emission intensity) versus time were

lirear for all coFplexe3- ro-t which luminescence was recorded. Excita-

tion was at 353 nm for -:nitoring experiments. For these experiments,

the 1 cm diameter laser team was shaped using a cylindrical lens to

give an irradiated area c 2x9 mm on the front window of a four clear-

side: cell. The moni-o'-ing beam traversed the full 1 cm width of the

irradiation cell, but tte excitation pulse was shaped to be 9 mm wide.

TKss the monitoring bea passes through 1 mm of unphotolyzed solution and

9 =, of photolyzed solution. The transmitted monitoring beam was reduced

onto the slit of the ronrcnromator, and exited onto a five-stage RCA

4':- photomultiplier. Sa=uration effects were avoided by employing a

mecnanical shutter. Typical entrance and exit slits in either experiment

were i m.

Emission spectra at 293 K were recorded using a Perkin-Elmer Model

£]-iCS fluorescence scectrophotometer and corrected for the Hamamatsu R928

P.t:-tiplier. Emissicn spectra at 77K were recorded using the Nd

.] 3s laser. Luminescence quantum yields were calculated using a known+ :-

22+E- zzer, u( bipy)3

P>:.tolysis experi-e-:s were performed with an Illumination Industries

-tedium pressure erecury arc lamp. Rolyn Optics Co. and Baird-

.. :-s interference filters (10 nm band pass) were used to isolate

.. r-..ation wavelerct', at 430 nm, 465 nm and 520 nm. Typical light

-3 -7 -1 74irts'sties were 10 - - Einstein s determined by Ferrioxalate

._2 r-, or Reineckate - nm and 520 nm) actinometry. Quantum yield

reasirements were rade for disappearance of starting material in the

mn -egicn. They were corrected for the small inner filter

effects due to product formation and changing degree of light absorption

when necessary. Reproducibility was within - 10g.

In the emission, .-onitoring and photolysis experiments, sample

solutions were filtered immediately before use through a 0.22 ;Im

Millipore filter and transferred to a lxl cm spectrofluorimeter cell.

The solutions were de-!=erated by argon purging for 20 minutes. The

t-perature of the solution in the cell was controlled to 0.1C by

circulating thermostatted water.

Luminescence data of solid W(CO) 5L were recorded using a triangular

cell with the front face at 450 to the exciting light. Conventional

absorption spectra were obtained by means of a Cary Model 14R and a

Hewlett-Packard 8450A recording spectrophotometers. Infrared spectra

were recorded in iso-octane using a Perkin-Elmer Model 281 spectrometer.

Eieental an= re performed by Analytical Facility,

California Institute of Technology.

, *.,o.-l edoerent

'.e wish to than,, Prcfessor H. Kisch for the sample of W(CO) 5

::e:J: cTinnoline). Tis investigation was supported in part by a

;~.~,. .itw , tie U. S. Office of Naval Research.

-24-

Refo'-ces and Notes

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(4) Strohmeier, W.; Gerlach, K.; von Hobe, D. Chem. Ber. 1961, 94,

164-168.

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-25-

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-26-

(35 Lin, C-T.; Sutin, i. J. Phys. Chem. 1976, 80, 97-105.

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(4 ) .1righton, 11. S.; "orse, D. L. J. Organomet. Chem. 1975, 97, 405-420.

(50) ',!righton, ,''. S.; Yorse, D. L.; Gray, H. B.; Ottesen, D. K.

J. km . Che-. S " 76, 98, 1111-1119.

r h ; .ho r, .S . ; .raha'son, H. D.; Iorse, D. L. J. Am. Chem. Soc.

1975, 912_

(52_ Luon; , J C.; -' & . U.; .righton, M. S. J. Am. Chem. Soc. 1979,

ICI, 1597-15.

(53) Vliek, R. . .; - csra, P. . Chem. Phys. Lett. 1975, 31, 487-491.

(5 Blakney, 3. - -i . F, Irnorq. Chem. 1971, 10, 2763-2770.

Frazier, C. Xisc H. lrtorq. Chem. 1978, 17, 2736-2744.

-27-

(56) Dahlgren, R. M.; Zink, J. I. _n~orq. Chem. 1977, 16, 3154-3161.

(57) Dahlgren, R. M.; Zink, J. I. J. Am. Chem. Soc. 1979, 101, 1440-1454.

(58) Dahlgren, R. M.; Zink, J. 1. Inorg. Chem. 1979, 18, 597-602.

(59) Boxhoorn, G.; Oskam, A.; Gibson, E. P.; Narayanaswany, R.; Rest, A. J.

Inorg. Chem. 1981, 20, 783-786.

(60) Wrighton, M.; Hammond, G. S.; Gray, H. B. J. Am. Chem. Soc. 1971,

93, 4336-4337.

(61) Wrighton, M.; Hammond, G. S.; Gray, H. B. Inorg. Chem. 1972, 11,

3122-3124.

(62) Lees, A. J.; Adamson, A. W. J. Am. Chem. Soc. 1980, 102, 6874-5876.

(63) Calvert, J. G.; Pitts, J. N. "Photochemistry" Wiley-Interscience:

New York, 1966; p. 298.

(64) Birks, J. B. "Photophysics of Aromatic Molecules", Wiley Interscience:

New York, 1970; p. 182.

(65) Fang, T-S.; Singer, L. A. J. Am. Chem. Soc. 1978, 100, 6276-6278.

(66) Ballardini, R.; Varani, G.; Wasgestian, H. F.; Moggi, L.; Balzani, V.

J. Phys. Chem. 1973, 77, 2947-2951.

(67) Flamigni, L. Radiat. Phys. Chem. 1979, 13, 133-138.

(68) Wagner, P. J.; Kemppainen, A. E.; Schott, H. N. J. Am. Chem. Soc. 1973,

95, 5604-5614.

(69) Porter, G. B. "Concepts of Inorganic Photochemstry",; Adamson, A. W.;

Fleischauer, P. F., Eds.; ; ,illey-Tnterscience: New York, 1975, pps 37-79.

(70) Kane-Maguire, N. A. P.; Toney, C. G.; Swiger, B.; Adamson, A. W.;

Wright, R. E. Inori. Chim. Acta, 1977, 22, LII-L13.

(71) See references in I and 51; also Wrighton, H. S., private communication.

(72) Gutierrez. A. R.; Adizjson, A. 11. ]J. Phys. Chem. 1978, 82, 902-907.

(73) Fukuda, R.; Walters, R. T.; Macke, H.; Adamson, A. W. J. Phys. Chem. 1979,

83, 2097-2103.

-28-

(74) Hazs-ar, C. G.; Parker, C. A. Proc. Roy. Soc. London Ser.A. .195 ,

2(7) l , 5E1--36.

(75) ,',ecner, E. E.; Ada-ison, A. 1. .J. Am. Chem. Soc. 1966, 88, 394-4104.

-29-

Table I

Absorption Band Mlaxima for W(CO) 5L Complexes at 298 K.

L Band Maxima (,., nm; (s), M- l cm- I)

Solvent

Methylcyclohexane Iso-octane Benzene THF Ethanol

4-ACpyr 404 (9650) 404 (8520) 402 (9810) 398 (9600) 398 (9540)442 (9590) 440 (8310)

4-B!pyr 405 (8780) 405 (7720) 403 (9530) 398 (9380) 398 (9310)435 (7790) 435 (6870)

4-CNpyr 404 (7280) 404 (6180) 404 (8040) 398 (8390) 398 (8370)454 (8680) 455 (7810)

4-FMpyr 402 (5990) 402 (5830) 402 (7280) 399 (6940) 398 (6850)470 (7640) 470 (6850)

_____ __ I

-30-

Erissicn Dataa for W(CO) 5L complexes at 298 K

L Emission !'axima (kK)b Luminescence Quantum Yield

Soli d Solventc (X10-4) SolventMethyl- Methyl-

cyclohexane Benzene cyclohexane Benzene

- .- r 17.25 16.03 15.90 5.3 1.6

18.75 16.23 16.42 7.7 2.3

- , 16.80 15.88 15.54 2.2 1.3

4-FP.,r 16.60 15.85 15.38 1.0

aThe excitation wavelength is 400 nm.

bCorrected for variation in photomultiplier response as a function of wavelength.

c5-'xIC- "de-aerated solutions.

-31-

Table I1 Solvent and Te-perature Dependence of Emission

Lifetime for 11(CO) 5 L Complexes

Temperature L Emission Lifetime (,s)a

(K) Solid Sol ventbMethyl -

cyclohexane Iso-octane Benzene THF Ethanol

278 4-ACpyr 1.401 0.554 0.562 0.258 0.057 0.0284-2,pyr 1.633 0.521 0.577 0.235 0.043 0.027

4-C ipyr 2,326 C.'38 0.435 0.269 0.075 0.0344-FPpyr 0.528 0.333 0.359 0.139 0.040 0.025

283 4-ACpyr 1.305 ^.519 0.532 0.243 0.048 0.0264-.pyr 1.529 0.527 0.520 0.222 0.034 0.0254-Cpyr 2.167 0..22 0.385 0.250 0.069 0.0314-F ''pyr 0.501 0.313 0.341 0.133 0.038 0.023

288 4-ACpyr 1.224 0.496 0.484 0.2254-B ;pyr 1.439 0.538 0.480 0.2134-C! pyr 2.056 0.393 0.355 0.2334-Fpyr 0.480 0.293 0.320 0.124

293 4-ACpyr 1.142 0.457 0,439 0.211

4-B;spyr 1.3,-t 0.505 0,441 0.1994-CIpyr 1 .944 C.389 0.327 0.219

4-F.Mpyr 0.462 0.273 0.307 0.115

298 4-ACpyr 1.072 0.-28 0.390 0.1974-EN'pyr 1.269 0.459 0.418 0.190

4-C,,pyr 1.822 3.350 0.297 0.2024-F,.pyr 0.433 0.251 0.280 0.109

303 4-ACpyr 1.011 9.393 0.352 0.1894-3';pyr 1.193 0.433 0.384 0.1774-CNpyr 1.721 C.343 0.269 0.1874-FMpyr 0.420 0.234 0.256 0.101

aThe excitation wavelength i- 353-

b 4-8x1"5M de-aerated solutions.

-32-

Table

Apparent A;.i','azion Energy, -,* and Frequency Factor, A, of W(CO)5L Complexes frc,-

Emission Li-ee:-e Data.

L Apparent Frequency Factor,

Energy (kcal -c!- (X10 sSolid "Solvent

Solid Solvent

-ethyl - M.ethyl -cycIo?.exare :s.-octane Benzene cyclohexane Iso-octane Benzene

4- Apyr 2.2 2.3 3.2 2.2 0.4 1.1 5.8 1.9

4- B'pyr 2.1 2.5 2.7 1.9 0.3 1.5 2.5 1.2

4- Cpyr 2.0 1.5 3.1 2.4 0.2 0.4 6.6 2.9

4- F;.,pyr 1.6 2.4 2.2 2.2 0.3 2.2 1.5 3.6

6-

Solvent and Tenperature D'lependence of Photosubstitution Quantum Yields for

5-7x13 5~ ' (C) 5( 4-C.Npyr,' in Solutions Containing 0.05 M Ethanol. Irradiation

Wavelengt:h is 465 nrn.

Temperature Quantum YieldSolvent

(K) M!ethyl - Iso-octane Benzene THF Ethanolcyclohexane

283 0.030 0.030 0.030 0.030 0.029

283 0.038 0.037 0.044

293 0.048 0.048 0.053

298 0.062 0.063 0.061

303 0/074 0.072 0.078

Tabl e 11 T

Temperature Dependence of P?'otosu~stitution Quantum Yield for 5-8xl0-5 M

W(CO)5(4-A~rpyr) and W(CO) 5~-~ in tethylcyclohexane Containing 0.05 M

Ethanol . Irradiation wavelEr.:, is 465 nm.

Temperature Quantum Yield

(K) W(CO) 5(4-ACpyr) W(CO)5(4-BNpyr)

283 0.016 0.014

288 0.020 0.018

293 0.025 0.021

298 0.030 0.027

303 0.040 0.035

Tire Le'.ends '

Figure 1 Ligard and solvent effects on the electronic absorption

spectra of W(CO) 5L complexes at 298 K.

a) ,O'CO) 5L in methylcyclohexane, L = 4-ACpyr (A),

4-Z'iyr (B), 4-CNpyr (C), 4-FMpyr (D) and CO (E).

b) "' C) 5 (4-CNpyr) in (-) methylcyclohexane and

(---! 1:1 (by Vol.) methylcyclohexane/benzene..

Figure 2 Corrected emission spectra at 298 K of a) W(CO) 54-ACpyr,

(b) W(CO) 5(4-BNpyr), c) W(CO) 5(4-CNpyr) and d)

W(CC)5(4-F.Ipyr); (- ) solid, (-) 6-8xi0 - 5 M1

1!(C:',,L in methylcyclohexane and (--) 4-6xI0 - 5 M

,.r,. ,L in benzene. Excitation wavelength is

4C5 n-i. Intensities are scaled arbitrarily to make

maxi-a equal.

Figure 3 Querchirg of 7.5xi0 -5 M W,(CO) 5 (4-CNpyr) processes

at 233 v by anthracene in methylcyclohexane containing

. ethanol. (0, To/t, o3 , 0/ , A, °/0).

Exci:-ion wavelengths are 0 530 nm, 520 nm and

Figjre" ! :ic absorption spectral changes accompanying

tFe "£5 nm irradiation (equal time intervals) at

297- of a) 5.4xl0"5 i W(CO) 5(4-ACpyr) and b)

I, (CO)5 (4-B;pyr) in methylcyclohexane.

go*-- :iJtions contain 0.05 M ethanol, the entering

1 i.¢

Fi !-e5 Excites-state electronic absorption spectra at

of " (4-ACpyr), 0 W(CO) 5(4-BNpyr) and

SW(CO>s'-(4 --C!' ,pyr) in a) methylcyclohexane and b)

benzene.

Ficgre 6 Trarsient electronic absorption spectra at 293 K

folloirg laser pulse photolysis of 0 Ui(CO) 5 (4-ACpyr)

0 ',:C )54-3 'pyr) and A W(CO)5 (4-CNpyr) in a)

nei..cyclohexane and b) benzene.

Figu;re 7 Test for unquenchable photolysis of W(CO)5(4-CNpyr)

in r7et'ylcyclohexane. Quencher is anthracene.

Figure 3 Energy v's distortion diagrams for W(CO) 5L. Heavy

horizontal lines represent thexi (thermally equilibrated

excited) states. Light horizontal lines represent

successive complex-solvent cage energies as a

vibrationally excited state relaxes to its thexi

state (only a few of the lines are shown). Heavy

vertical lines denote radiative processes, wavy

lines ter:te non-radiative processes.

10 A

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0

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s u , j i ) s ,,) u DAI l@.

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3 M [o]

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0.6-a 0

0.5-

0.4-

V2

0.3- 34

0.20.10-

O. I I "

0 .5-I *

30C"' Z ? 400 4 5O 500 550Wavelength, am ,04

cl- 0.4- I --- 1 ln 0 nU/. .

!I I

4 - 0 o

' 0

2 0

00 I I[-4 --0 b

000

4- 00

2-

400 02)600 700Wavelength, nm

b . /" .

8a

00

0 r.->.5

6-

0

00

0 °00 50 0 0 00 !

80

6-

00

0~

205

-,,- I *!

-400 500 600 700Wavelength, nm

7..-, t. ,j,.t , ... . , ,,i., -'- z . . ,, ,. .- ,,..I 4"l '" '= '

-- -i - __ _ _ _ _ _ _" _ _ _ _ _ _

I- - t ) 6p

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AAt~Th IiN~44~zzzzzmzzzr

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>7A~u3

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