Vol. 17 No. 5 CHINESE JOURNAL OF CHEMLSTRY 1999

Synthesis , electrochemistry and fluorescence of four new Ru ( phen) 3 + derivatives

WANG, Peng(4 . a ) ZHU, Guo-Yi" (%R%) Laboratory of Electmad*d Chemistry, C h a n g b Institute of Applied C M t r y ,

Chinese A m d a y of Sc iem , C h a n g b , Jilin 130022, China

Abshsct Four typical LB monolayer film materials, Ru( phen)z+ complexes with one ligand attached to dif- ferent long chain alkyl amides, were designed and synthesized. 'Iheir chemical structures were identified by the techniques of FT-IR, 'H NMR and ESI-Ms. Also, UV-Vis, electrochemistry and fluorescence of these complex- es are reported.

Keyworrls Ru( phen):' derivatives, synthesis, electrochemistry, fluorescence.

Introduction

Ru(II) polypyridine complexes have been one type of the molecules most extensively studied and most widely used in research laboratories during the last twenty years. A unique combination of chemical stability, redox properties, excited state reactivity, luminescence emission, and the excited lifetime has attracted the attention of many research workers to these compounds. ' firstly observed the electrochemiluminescence (ECL) from a monomolecule of a Ru ( bpy):' -based sdactant con-fined to the surfaces of in-doped tin oxide, Pt and Au electrodes. After that, monolayer films of Ru( bpy). (bpy-CIg)'+ , on a Langmuir trough contacted by the horizontal touch method with an indium- tin oxide coated glass or a hghly oriented pymlytic graphite electrode, were characterized by imaging their ECL emission by Bard's p u p . 3

It is known that ECL efficiency of Ru(phen):+ is higher than that of Ru( bpy)i+ . 4 In order to pre-

pare highly efficient ECL Langmuir monolayer films, we designed and synthesized four new Ru( phen)i+- b m l complexes with different long hydrocarbon tails as shown in Scheme 1.

In 1988, Zhang et al .

Experimental

Reagents

RuC13.xHzO was obtained from Kunming Institute of Noble Metals and used without further purifi

Received December 28, 1998 ; accepted March 29, 1999. Project supported by the Minishy of Science and Technology of China (No. %-A23-03-01]

WANG & ZHU Ru( phen);+ derivatives 503

Scheme 1 Synthesis of new Ru( phen):+ -based complexes

cation. Acetonitrile was dried by CaH2 and distilled before use. b y 1 chloride, myristoyl chloride, pahtoyl chloride and steamy1 Chloride were all purchased from ACROS Corporation. The key starting materials, ~-amino-l,lO-phenanthroline and cis-Ru ( phen)ZC12, were prepad as reported in refer-

ences. 5,6 The other reagents used were a~ analytical reagents.

I n f d spectra (KBr pellet) were recorded on a Bio-RAD I%-7 spectrometer. 'H NMR spectra were obtained at room temperature on a Varian Unity 400 spectrometer. Samples for 'H NMR were dis- solved in DM%- d6. Chemical shifts were expmsed in ppm using "Ills as the i n t e d standard. ESI-MS spectra were performed on a Finnigan MCT LCQTM mass spectrometer using DMF as the matrix. UV-Vis were obtained on a M Y - I spectrometer. F l u m e n c e spectra were taken on a Shimadzu RF-5ooO fluo- rescence spectrometer at 2 P C . Cyclic voltammetq experiments were conducted on a CHI 660 electro- chemical station. The working electrode was Au disk and all potentials were measured relative to a SCE electrode. The counter electrode was F't wire. Scan rate was 100 mV/s .

0.9761 g (0.005 mol) of 5-amino-l, 10-phenanthroline, 0.504 g (0.006 m l ) of sodium &&n- ate and 60 d of acetonitrile were fully mixed in a 250 d round bottom flask with one mouth connected to a nitrogen-filled balloon. After the solution was cooled in an ice-water bath at 5 "c , a solution of lau- my1 chloride (1 .OW g, 0.005 mol) in acetonitrile (40 d) was slowly added to the above solution. The reaction was carried on for 5 hours, and the resulting solution was filtered and washed with acetonitrile, 5 % sodium dicarbonate aqueous solution and water in turn. After drying in uucuo, pink solid l a was

obtained inayieldof73%. v,,(KBr): 3258(NH), 1658(C=O) cm-'. &(DMm-d6): 0.95(t, J =

504 Chinese Journal of Chemistry Vol. 17 No. 5 1999

6 . 8 H z , 3 H , CH3) , I . 3 1-1 .39( br, 16H, CH2 x 8 ) , 1 .79-1.82( m, 2H, CH,) ,2.70( t , J = 7.2 H z , 2H, CH?), 7.97(q, J = 4 . 0 H z , lH, 8-H), 8.06(q, J = 4 . 0 H z , lH, 3-H), 8 . 4 2 ( ~ , lH, 6- H ) , 8.76(d, J = S . O H z , lH, 7-H), 8.95(d, J = 8 . 4 H z , lH, 4-H), 9.18(d, J=4 .0Hz, lH, 9-H), 9.28(d, J = 4 . 0 H z , lH, 2-H), 10.52(s, lH, NH). rn/z(ESI-MS): 400 .2( [M+Na]+) .

u,(KBr): 3260 (NH), 1658(C=O) cm-'. &(DMSo-ds): 0.96(t, J = 6 . 8 Hz, 3H, CH3) , 1.33-1.39(br, 20H, CH2x10), 1.79-1.82(m, 2H, CH2), 2.65(t , J = 7 . 2 H z , 2H,

Synthesis of l e d is almost the Same as that of la . l b

CH?) , 7.86(q, J = 4 . 0 H z , lH, 8H), 7.93(q, J=4 .0Hz, lH, 3-H), 8 . 2 9 ( ~ , lH, 6-H), 8.56 ( d . J = 8.0Hz, 1H,7-H) , 8 . 7 2 ( d , J = 8.8HZ, lH,4-H) , 9 . 1 5 ( d , J = 4.4Hz, 1 H , 9 - H ) , 9.24(d, J = 4 Hz, lH, 2-H), 10.21(s, 1H, NH). rn/z(ESI-MS): 428.3([M+NaIt) .

u,(mr): 3256(NH), 1658(C=O)cm-I. &(DMSO-d6): 0.95(t, J = 7 . 2 Hz, 3H, CH3) , 1.32-1.39(br, 24H, CH2 x 12), 1.78-1.81(m, 2H, CHZ), 2.66( t, J = 7.2 Hz, 2H,

1 C

C H ? ) , 7.86(q, J = 4 . 0 H z , lH, 8H), 7.94(q, J = 4 . 0 % , lH, 3-H), 8 . 2 9 ( ~ , lH, 6-H), 8.57 ( d , J =4.OHz, 1H,7-H) , 8 . 7 6 ( d , J =4.0Hz, 1H,4-H) , 9 . 1 3 ( d , J = 8.4Hz, 1 H , 9 - H ) , 9.22(d, 5 = 8 . 4 Hz, lH, 2-H), 10.32(s, lH, NH). m/z(ESI-MS): 456.3([M+Na]+).

u,(KBr): 3262(NH), 1660(C=O)cm-l. &(DMSO-ds): O . % ( t , 5 = 6 . 8 Hz, 3H, CH3), 1.33-1.40(br, 28H, CH2x14), 1.79-1.82(m, 2H, CHZ), 2.65(t, J = 7.2Hz, 2H,

I b

CH?), 7.89(q, J=4 .0Hz, lH, 8H), 7.97(q, ]=4.0Hz, lH, 3-H), 8 . 3 2 ( ~ , l H , 6-H), 8.62 (d,J=8.4Hz,lH,7-H),8.75(d,J=8.4Hz,lH,4-H),9.16(d,J=4.OHz,lH,9-H), 9.25(d, J = 4 . 0 Hz, lH, 2-H), 10.24(s, lH, NH). m/z(ESI-MS): 484.4([M+Na]+).

~is-Ru(phen)~Cl~ (0.5684 g, 1 mmol) and l a (0.4773 g, 1 mmol) were stirred in refluxing methanol (20 mL) and water ( 5 mL) for 9 hours. The resulting solution was separated by filtration and washed with methanol (8 mL) . The combined filtrate and washing solution were treated with a solution of sodium hexaflurophosphate (5.0 g) in water (25 mL) . The resulting solution was cooled in an ice bath for 3 hours. The resulting precipitate of orange microcrystal was collected by filtration, and dried in wzc-

UO (p205). u,(mr): 3260(NH), 1698(C=O), 840(P-F) cm". &(DMSO-d6): 0.95(t, 5 ~ 7 . 2 Hz, 3H, CH3), 1.33-1.41(br, 16H, C H ~ X ~ ) , 1.81-1.83(m, 2H, CHZ), 2.68(t, J=7 .2Hz, 2H, CH?), 7.89-7.91(m, 6H, 3-H and 8-H of phen and la ligands), 8.19-8.22(m, 6H, 2-H and 9-H of phen and l a ligands) , 8.51 ( s , 4H, 5-H and 6-H of phen ligands) , 8.78( s, 1 H , 6-H) , 8.88-9.91(m, 7H, 4-H and 7-H of phen and l a ligands and 6-H of l a ligand), 10.50(s, lH, NH) . m/z(ESI-MS) : 983.6( [ M - PF,)] + ) , 419.3( [ M - 2PF6I2+ ) .

Synthesis of 2b-d is almost the same as that of 2a. 2b u,(mr): 1699(C=O), 842(P-F)cm". &(DMSO-d6): 0.95(t, 3 = 7 . 2 Hz, 3H,

CH3), 1.33-1.40(br, 16H, CHlxlO), 1.80-1.82(m, 2H, CH2), 2.69(t, J = 7 . 2 H z , 2H, CH2 ) , 7.92-7.94( m, 6H, 3-H and 8-H of phen and l b ligands) , 8.20-8.24( m, 6H, 2-H and 9- Hofphenandlbligands), 8.50(s,4H, 5-Hand6-Hofphenligands), 8.77(s, lH, 6-H), 8.- 8.93(m, 7H, 4-H and 7-H of phen and l b ligands and 6-H of l b ligand), 10.52(s, lH, NH). m / z

u,(mr): 1701 ( c = o ) , 841(P-F)cm-'. a ~ ( D M s 0 - d ~ ) : 0.94(t, J = 7 . 2 Hz, 3H,

( f i l - M s j : 1011.6( [ M - PF6)] + ) , 433.3([ M - 2PF6I2' ) .

2c

WANG & ZHU Ru( phen):+ derivatives 505

CH3), 1.32-1.39(br, 16H, CH2x 121, 1.82-1.84(m, 2H, CHz), 2.69(t, .! = 7 . 2 Hz, 2H, CHz), 7.91-7.93(rn, 6H, 3-H and 8-H of phen and lc ligands), 8.20-8.23(m, 6H, 2-H and 9- Hofphenandlcligands), 8.51(s, 4H, 5-Hand6-Hofphenligands), 8.79(s, lH, 6-H), 8.88- 9.91(rn, 7H, 4-H and 7-H of phen and IC ligands and 6-H of lc ligand), 10.49(s, lH, NH). m/z (B1-m) : 1039.7( [ M - PF6) ] + ) , 447.4( [ M - 2pF6I2' 1.

u-(KBr): 1697(C=O), 840(P-F)cm-'. ~H(DMSO-~~): 0.95(t , 5 = 7 . 4 Hz, 3H, CH3), 1.30-1.38(br, 16H, -2x14), 1.7!+1.81(m, 2H, C H z ) , 2.70(t, .!=7.2Hz, 2H, CH2), 7.88-7.90(rn, 6H, 3-H and 8-H of phen and Id ligands), 8.19-8.2l(m, 6H, 2-H and 9- Hofphenandldligands), 8.51(s, 4H, 5-Hand6-Hofphenligands), 8.50(s, lH, 6-H), 8.88- 8.90(rn, 7H, 4-H and 7-H of phen and Id ligands and 6-H of Id ligand), 10.51(s, lH, NH). m/z

2d

(B1-M) : 1067.7( [M - PF6)] + ), 461.3( [M-2m6IZ+ ).

The IR absorption peaks (C = 0) of 2 appear at wavelengths of about 1700 m-' , which are abnor- mally blue-shifted 40 an-' cmnpad with that of 1. We think these may be an important contribution of d - x * feedback ef€ect.

Electrospray mass s w

In the last year electmpray mass spectrometry has become a popular tool for the characterization of hi&-nuclearity and/or hifly charged coodination The principal mass spectral peaks (see ExperirnentaI section) in every case confirm the formulations of the complexeS. Generally, loss of both the hexahomphosphate anions results in a doubly-charped fragment which appears at the m / z value com- sponding to half the value that is expected for a + 1 fI.sI...t.

The 'H NMR spectra of 2 were assigned acmrdmg to those of the modd coxnpkx Ru(phen)3(PF6>2 which were completely assigned in view of m p h g constant. 2-H and 9-H of ligand~ occur at higher field than 4-H and 7-H due to a local shieldmg effect h the spacial adjacent ligand.

The four Ru( II) complexes 2 all exhibit around 265 nm adsorption in the W xegion, which can be assigned to heternmatic e x * transitions. "hey also exhibit typical d+x* MLCl" transitions at about 440 nm.

506 Chinese Journal of Chemistry Vol. 17 No. 5 1999

Electrochemistry

The electrochemical properties of 2 were investigated by cyclic voltammetry. All new tris ( 1 , l O - phennanthroline) nithenium ( II ) hexafluomphosphate derivatives 2a-d undergo a single-electron re- versible oxidation when the potential scans from 1.15 to 1 .42 v , as shown in Fig. 1. Similar results were obtained for 2b-d. Table 1 shows cyclic voltammetric data for 2a-d.

I I5 120 I 2 5 1 3 0 135 I40 1 4 5 E (mVvs SCE)

Fig. 1 Cyclic voltammogram of 2a over a potential of 1.15 to 1.50 V at a scan rate of 100 mV/s.

Table 1 Cvclic voltammetric data for 2-d at a scan rate of 100 mV/s

28 1.297 1.236 1.267 61

2b 1.298 1.236 1.267 62 2c 1.298 1.237 1.268 61 2d 1.299 1.236 1.268 63

Fluorescence absorption and emission

Fluorescence absorption and emission data of 0.1 m V L 2a-d in ethanol at room tempera- are

shown in Table 2. These intense absorption bands are due to the MLCT transition where an electron is p m t e d from the metal centered tZg orbital into a ligand centered 51 orbital. The intense emission oc-

c u s at lower energy than the ligand centered X * - T phosphorescence does. There is a significant contri- bution to the excited state from an interaction between the metal d orbitals and the ligand p system.* Many studiesg have indicated that the ECL spectrum of each Ru( 11) complex is very similar to its fluorescence spectrum, so the fluorescence spectra of 2 hinted ECL spectra of 2.

WANG & ZHU Ru( phen): ' derivatives 507

Table 2 Data of fluorescence specma for tris( l,lO-phenmhline)mthenium( II) hexafluorophosphate derivatives 2-d

Compound heorption (m) L i o n (m)

2a

2b 2€

479 480 479

592

592 594

2d 478 595

Conclusion

From the above results, all new Ru (II) complexes 2 might behave as good materials for electro- chemiluminescent Langmuir mnolayer films. Further experiments are underway to prepare and investigate LB membranes based on the new Ru( II) complexes.

References

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2. 3. 4. 5. 6. 7.

8. 9.

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(JUNG, X . H . ; DONG, L . J . )