Indian Journal of Chemical Technology Vol. I 0. September 2003, pp. 519-524

Articles

Fluorescence and lasing characteristics of fluorescein calix[4]aryl hydroxamic acid

M S Gidwani, S K Menon* & Y K Agrawal

Department of Chemistry, School of Sciences, Gujarat University, Ahmedabad 380 009, India

Received II July 2002; revised received 3 March 2003; accepted I9 May 2003

A new fluorogenic calix[4]arene has been synthesized by reacting acid chloride of fluorescein and partially reduced nitrocalix[4]arene. The synthesized compound is characterised by UV, NMR and mass speftra. Fluorescence characteristics of N,N'-(fluorescein)-7 ,19-dinitro-25,26,27 ,28-tetrahydroxy-1,13 calix[ 4]aryl hydroxamic acid have been investigated in methanol, chloroform, toluene and dioxane.and tested for lasing performance. Relative output, lasing wavelength and laser yield of the compound are reported. The dependence of solvent polarity on its lasing properties are discussed.

Several classes of organic compounds have been demonstrated to give laser action when pumped by means of a N2 laser1

'2

• Coumarin and Rhodamine dyes are popularly used owing to their high laser yield, photostability, available tuning spectral range and high solubility in common solvents3

.4. Several attempts have been made to find new dyes with lasing properties comparable to those of commercial dyes by making changes in the functional group5

-9

. The fluorescence and lasing properties of 3-[2-substituted­hydrazino-5-thiazole]-7 -hydroxycoumarin have been reported 10

• These substituted coumarin dyes showed larger laser yield than the reference coumarin 480 whereas substituted N-aryl-coumarin-3-hydroxamic acids 11 exhibited less laser yield (ratio of the maximum output laser intensity and the efficiency) 12

•

The lasing characteristics of poly(N-acrylidine) Schiff bases were also studied 13

.

[n the present investigation the synthesis, characterisation and the lasing characteristics of a fluorogenic macrocycl compound, fluorescein calix[4]aryl hydroxamic acid (I), have been described and its fluorescence characteristics reported in various solvents of different polarities.

Experimental Procedure

Chemicals and Reagents All the chemicals used are of A. R. Grade of E.

Merck unless otherwise specified. Methanol,

*For correspondence (E-mail: sobhanamenon@rediffmail.com; Fax: 6308545)

chloroform, toluene and dioxane are purified as described elsewhere 14

•

Apparatus Melting points are taken in a sealed capill ary tube

using a Toshniwal (India) melting point apparatus and are uncorrected. Infrared spectra are obtained on Ff­IR/410, JASCO spectrometer. The 1H NMR spectra are recorded on DRX 300 spectrophotometer operating at 300 MHz for proton in CDCI3 with TMS as internal standard.

The FAB mass spectra are recorded on a JEOL SX 102/DA-6000 mass spectrometer/data system using Argon/Xenon (6 kY, 10 rnA) as the FAB gas. The accelerating voltage is 10 kY and the spectra are recorded at room temperature. m-Nitrobenzyl alcohol (NBA) is used as the matrix and the matrix peaks appeared at rn/z 136, 137, 154, 289, 307.

The ultraviolet spectra are scanned on Hitachi Model UV-3210 spectrophotometer. Fluorescence spectra are recorded on Hitachi F-2000 spectrofluorimeter. Fluorescence lifetimes are measured on SLM 4800 phase fluorimeter.

The lasing characteristics of the dyes has been tested using commercial N2 laser as a pump source (Molectron UV 1000) associated with a commercial dye laser (Molectron Dl 400). The N2 laser has a peak power of 1 MW and a pulse duration of l 0 ns. The repeatation rate is 20 Hz.

Synthesis of nitrocalix[ 4 ]arene In a 250-mL round bottom flask fitted with a reflux

condenser, 15 g (0.11 mol) p-nitrophenol, 8.1 g

Articles

(0.11 mol) formaldehyde (37%) and 15 mL cone. hydrochloric acid are taken. The mixture is heated on the water bath (80°C) for 6 h with occasional stirring. The white solid thus obtained is filtered. washed with hot water and finally with hot alcohoL The melting point of this white solid was found to be 140-142°C and yield was 10.5 g (70% ).

Partial reduction of nitroctzJix[4]arene 1n a 100-mL three necked round bottom flask

equipped with a condenser and a mechanical stirrer 20 g (0.03 mol) of nitrocalix[4]arene is taken in 50 mL DMF and is stirred till the temperature of reaction mixture reached 0°C- (-5°C). Then 4-5 g of Raney­Ni (W-2) is added followed by 20 mL (0.41 mol) of hydraziDe hydrate (80%) which is added dropwise. The reaction mixture is stirred below 0°C for 1h. After an hour, the calix[4]arene hydroxylamine is filtered and the filtrate, in situ, is directly used for coupling, considering its yield as 60% i.e. 12 g.

Synthesis of fluorescein acid chloride In a 100-mL round bottom flask, equipped with a

reflux condenser and calcium chloride guard tube, are taken 13.3 g (0.04 mol) of fluorescein alongwith 15 mL (0.21 mol) thionyl chloride. The mixture is refluxed on waterbath · for 6-8 h. A clear reddish coloured solution is formed and excess of thionyl chloride is distilled under vacuum.

Coupling of calix[4]arene hydroxylamine with fluorescein acid chloride

ln a 100-mL conical flask fitted with a dropping funnel, freshly prepared in situ 12 g (0.02 mol) of calix[4]arene hydroxylamine is placed. An aqueous suspension of 4.87 g (0.06 mol) of sodium bicarbonate in I 0 mL of water is added and stirred. After the mixture is cooled to 0°C - (-5°C), 13.3 g (0.04 mol) of fluorescein acid chloride dissolved in 25 mL dioxane is added dropwise over 45 min and the stirring is continued for another 15 min. Almost the entire amount of fluorescein calix[ 4 ]arene hydroxamic acid formed is precipitated as yellowish white granular solid. It is filtered off, washed with water and is recrystallized twice from .chloroform-n­heptane mixture (1:1); giving a yellowish white compound with m.p. 175°C and yield 7.8 g (65%).

Lasing properties The compounds are dissolved in methanol,

chloroform, toluene and dioxane and introduced in a

520

Indian J. Chern. Technol. , September 2003

Fig. 1-N,N' -fluorescein-?, 19-dinitro-25,26,27,28-tetrahydroxy-1, 13-calix( 4 )aryl hydroxamic acid(!).

circulating cell of the dye laser. The coumarin 480 is used as a reference because its lasing properties are easily and readily optimized in order to get a laser yield as high as possible.

A non calibrated thermopile (Molectron Joule meter) was used to measure the relative output energy of the tested compounds and Coumarin 480 for comparison under experimental conditions.

The fluorescence quantum yields are measured using quinine sulphate in 0.1 N H2S04 (Q> = 0.52) and

. 0 0 d d 1516 rhodamme I I ( Q> = I. ) as stan ar s · .

Results and Discussion

Synthesis and properties of fluorogenic calix[4]arene

The method 17 for the synthesis of nitrocalix[4]arene is simple and of single step with reasonable yield. The p-nitrophenol is reacted with formaldehyde using acid catalyst. The mixture is treated on waterbath for 6 h to get the nitrocalix[4]arene.

The complete reduction of substituted nitrocalix[4]arene is reported by Arduini et a/.18 using Pd/C catalyst and by Shinkai et al. using N2HJFeCI3 on activated charcoal 19

• In the present investigation, the nitrocalix[4]arene is partially reduced using a comparatively cheap catalyst Raney nickel, using hydrazine hydrate (80%) below 0°C. The synthesis is shown in Scheme I.

The compound, N ,N' -(fluorescein)-7, 19-di nitro-25 , 26, 27, 28-tetrahydroxy-I,l3 calix[4]aryl hydrox-amic acid (Fig. I), is yellowish white crystalline solid with molecular weight I203 .50 corresponding to molecular formula C68~3N40 1 s with a sharp m.p. 175oC. It is insoluble in water but soluble in organic solvents like methanol, chloroform, toluene, dichloromethane, dioxane, etc.

This synthesized compound is characterised by lR , NMR and Mass Spectra.

Gidwani et al.: Fluorescence and lasing characteristics of fluorescein calix[4]aryl hydroxamic acid Articles

p-nilrophenol

HCI

6n

nitrocol ix( 4 )orene

HOiO

farmolden)de

NH2NH '! Roney-Ni (ao,;) (W-2J 0-( - 5\:) OMF

0

fluorescein

fluorescein acid chloride cal ix( 4 )arene hydrox)4omine

dioxonel NoHCO, o-c-(-5-cl H2o

0

C=O

J :1E11I -OH NO,

0 0

l

N,N' fluorescein-7, 19-dinitro- 25,26,27,28-tet roh )droxy-1, 13- colix( 4)ar~ n)droxomic ocid (I)

Scheme !-Synthesis of N,N'-fl uorescein-7, 19-dinitro-25, 26, 27, 28-tetrahydroxy-1, 13-calix( 4)aryl hydroxamic acid (I)

Infrared spectra

0-H stretching vibrations The broad and short bands around 3600 ± 50 cm- 1

and 3400 ± 25 cm-1 are assigned to phenolic -OH of the calixarenes and VoH of the hydroxamic functional group (-N-OH). It is well-known that absorption due to Vo-H stretching vibrations, when free, appear around 3650 cm- 1

, however hydrogen bonding shifts these bands to lower frequencies·20

'21

. In the present case, the shifting of absorption band to lower frequency may be attributed to the intramolecular hydrogen bonding between the lower rim hydroxyl groups of the calixarene and the acidic (0-H) which is placed in very close proximity to the polar carbonyl group (C=O).

>C=O stretching vibrations The stretching vibration due to >C=O of lactone.

appears at 1706 cm-1• According to John et a/. 21 such

system is considered as a a-pyran (fused ring system) and for that the carbonyl band is assigned in the region of 1760-1740 cm-1

• But due to the subst itution in the fused pyrone ring system, the band shift to lower wavelength. The conjugation also shifts the band of carbonyl to the lower frequency 22

.

The band at 1617 cm- 1 is assigned to the >C=O of hydroxamic group. Mathis23 has assigned this band to benzo, propiono and substituted benzo hydroxamic acid at 1640±30 cm-1

• The H-bonding lowers the (>C=O) by 10-50 cm-1

• The conjugation of >C=O with >C=C< lowers the absorption band by about 50 cm- 1•

C-N stretching vibration A medium absorption band at 1347 cm-1 have been

assigned to C-N vibration. This band in aromatic tertiary amines appears20 in the region of 1360-1 3 10 cm- 1 and in N-ary! hydroxamic acids also it has been reported24 at 1380 ±50 cm-1

•

N-0 stretching vibration A sharp band at 952 cm-1 may be attributed to N-0

stretching vibration. The presence of sharp bands at 1319 cm-1 and 1568 cm-1 are similar to that observed in nitrocalix[4]arene, suggesting the presence of -NOc group in the compound.

1 H NMR spectra The 1H NMR spectra are recorded in the range of 0-

14 ppm in CDC13 using TMS as internal standard. Chemical shifts are expressed in ppm scale. The 1 H­NMR spectra shows a doublet at 5.14 ppm due to the -CH2 proton. A number of peaks due to aromatic protons appear at 7.71 ppm. The singlet of hydroxyl protons on the calix[4]arene lower rim appears at 13.26 ppm and due to the hydroxamic group appears at 10.56 ppm. The singlet obtained at 8.05 ppm is the characteristic signal of the C5H of fluorescein.

13C NMR spectra In the 13C NMR spectra, the chemical shifts (ppm)

observed are 126.6 (HON-C), 129.3 (O=C), 136.8 (02N-C), 168.9 (OH-C), 65 .8, 65 .9, 115 .6, 11 9.1. 121.4, 133.5, 124.0, 127.2, 127.3, 129 .0, 129.3, 133.1. 133 .3, 133.5 and 135.4 (aryl C).

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Mass spectra The m/z values obtained are 1149, 1086, 989, 963,

907,858,812,769,734,675,661,639,579,504,461, 403,391,369,352, 325,289,267,224,207,193,120, 108.

UV spectra The absorption maxima of the fluorescein

t alix[4]aryl hydroxamic acid in methanol, ' hloroform, toluene and dioxane are given in Fig. 2. 'Che fluorescence spectra in the same series of solvents are given in Fig. 3. It has been observed that in all the solvents, the compound showed maximum absorption at 300 nm. The molar absorptivity values obtained are also in the same range in all the solvents. The data is represented in (Table 1).

Fluorescence spectra The fluorescence spectra of fluorescein calix[4]aryl

hydroxamic acid of 2.5x 10"" M in methanol, chloroform, toluene and dioxane are given in Figs 3 and 4. The excitation and emission maxima of the compound in all the four solvents occur almost at the same wavelength (.Aex = 220 nm; .Aem = 448 (chloroform), 445 (toluene), 444 (dioxane), except in methanol which exhibits emission maxima at 525 nm. The dyes show a single lifetime in all the solvents. The lifetime (2.7 ns) and quantum yield (0.06) are more in methanol as compared to other solvents (Table 2). However, it can be concluded, from the data of quantum yield of the fluorescein substituted macrocyclic compound, that there is a quenching effect on the fluorescence properties of fluorescein by attaching the moiety on a macrocyclic compound like calix[4]arene. The quenching may also be due to the presence of -N02 group on the upper rim of the calix[4]arene at alternate positions25 as represented in (I).

Lasing properties The laser effect of the compound has been tested

using a commercial N2 laser as a pump. The tuning

Indian J. Chern. Techno!., September 2003

range with the la<>er yield at the optimum concentration of the compound 10 methanol , chloroform, toluene and dioxane are given in (Table 2). The results show that the laser yield is at its maximum (0.85) in methanol whereas the lasing properties are relatively very less in other solvent media. Since there is a striking difference in the polarity of methanol (dielectric constant, 32.70) compared to the other solvents studied viz. chloroform

.. ~ -e 0

"' J:)

<

0 1 250 300

I 500 600

wavelength.nm

Fig. 2- UV -vis absorbance spectra of fluorescein calixl41aryl hydroxamic acid in methanol, chloroform. toluene and dioxane.

o - r--~~~--~--~------,-----~

0 400 6()0 600

Wavelength. nm

Fig. 3-Fluorescence spectra of fluorescein calix[4]aryl hydroxamic acid in methanol, chloroform, toluene and dioxane.

Table 1-Fluorescence data of N ,N' -(fluorescein)-?, 19-dinitro-25,26,27 ,28-tetrahydroxy-1, 13 calix[ 4 ]aryl hydroxamic acid in methanol, chloroform, toluene and dioxane

Solvent Ex). Em). Lifetime Quantum yield Concentration Excitation coefficient (nm) (nm) (ns±0.1) ±0.02 (M) xl04

Methanol 220 525 2.7 0.06 2.5xl04 1.8

Chloroform 220 448 1.9 0.04 2.5xl04 1.6

Toluene 220 445 1.8 0.04 2.5xl04 1.5

Dioxane 220 444 1.3 0.03 2.5xl04 1.2

Fluorescence quantum yield is measured using quinine sulphate in 0.1 N H2S04, $=0.52

522

Gidwani et al.: Fluorescence and lasing characteristics of fluorescein calix[4]aryl hydroxamic acid Articles

Table2-Laser characteristics of N,N'-(fluorescein)-7,19-dinitro-25,26,27,28-tetrahydroxy-1, 13 calix[4]aryl hydroxamic acid in methanol, chloroform, toluene and dioxane

Solvent A.max, nm N2 Laser Pumping Laser Yield Optimal concentration mole L-1

(a) A.max, Tuning range, (b) (c)

Methanol

Chloroform

Toluene

Dioxane

570

505

490

485

nm

580

510

500

495

(a) Laser wavelength at which the laser yield is maximum (b) Laser yield relative to the coumarin 480 nm (Amax) (c) Optimal concentration at which the laser yield is maximum

200

Coumarin480

0+--L~----~--~--~~---+~-~

500 520 580 eoo ~.nm

nm

560-584

505-520

495-505

490-500

Fig. 4-Tuning range of standard Rhodamine 6G, coumarine 480 and N,N' -fluorescein-7, 19-dinitro-25,26,27,28-tetrahydroxy I ,13 calix[4]arylhydroxamic acid.

(dielectric constant, 4.81), toluene (dielectric constant, 2.57), and dioxane (dielectric constant, 2.21), it can be concluded that the laser yield of the compound is sensitive to the polarity of the medium. Further, methanol is also a hydrogen bonding solvent and may form non-covalent structures with the compound, which lead to high laser yield compared to other solvents. A similar dependence was reported earlier 12

also. The variation in laser yield as a function of

emission wavelength are studied and it has been noticed that due to very small overlap between the absorption and emission spectra of the investigated compound, the center of tuning range does not depend upon concentration as observed in some commercial dyes such as rhodamine dyes. The comparative tuning curve of the present compound with rhodamine R6G,

0 .85 2.5x l0-4

0.50 2.5x l0-4

050 2.5x l0-4

0.50 2.5x l0--l

and coumarin 480 is shown in Fig. 4. The optimum concentration at which the laser yield is maximum are given in (Table 2).

Acknowledgement The authors acknowledge BARC, Mumbai for the

laser studies. Financial assistance given by CSIR. New Delhi is gratefully acknowledged.

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