2-(4-取代苯基)-4,5-二(4-氯苯乙烯基)咪唑化合物的合成和荧光性能

Synthesis and fluorescence properties of 2-(4-substituted phenyl)-4,5-di(4-chlorostyryl) imidazole compounds

以2,3-丁二酮和4-氯苯甲醛为原料,在哌啶催化下合成了1,6-二(4-氯苯基)-1,5-己二烯-3,4-二酮(MTCl),再以MTCl、4-取代苯甲醛及醋酸铵经Debus反应合成了7个2-(4-取代苯基)-4,5-二(4-氯苯乙烯基)咪唑化合物(1a-1g).采用FT-IR、1H NMR、13C NMR以及质谱(MS)表征了MTCl和1a-1g的结构.荧光分析表明1a-1g的DMF稀溶液(1×10-5mol/L)荧光发射波长在439～554 nm的蓝绿区,与2-苯基-4,5-二(4-氯苯乙烯基)咪唑(1e)相比,2-苯环上有取代基时使1a-1g的荧光发射波长红移,但相对量子产率随着2-苯环上取代基给电子能力增大而降低,值得注意的是致钝基团氰基不影响相对量子产率.酸碱影响实验结果表明:2-(4-二甲氨基苯基)-4,5-二(4-氯苯乙烯基)咪唑(1a)对酸最敏感,1a的DMF稀溶液加入5μL的硫酸溶液(0.03 mol/L)后荧光强度迅速达到最小; 2-(4-氰基苯基)-4,5-二(4-氯苯乙烯基)咪唑(1g)对碱较敏感,1g的DMF稀溶液加入5μL的四丁基氢氧化铵水溶液(TBAH,2.0%)后荧光几乎消失,加酸后荧光性能恢复,具有酸/碱开关效应; 2-(4-甲氧基苯基)、2-(4-羟基苯基)、2-(4-甲基苯基)和2-苯基取代咪唑衍生物的DMF稀溶液加入少量的TBAH后,它们的"双"荧光发射峰强度同时减弱,加酸能恢复荧光性能,而加入少量稀硫酸时其中一个峰的强度减弱,另外一个增强,加碱能恢复荧光性能.

1,6-di（4-chlorophenyl）-1,5-hexadiene-3,4-diketone （ MTCl ） was synthesized by using 2,3-butanedione and 4-chlorobenzaldehyde as materials under piperidine catalysis. Then seven 2-（4-substitutedphenyl）-4,5-di-（4-chlorostyryl） imidazole （ 1a - 1g ） compounds were synthesized via the Debus reaction from MTCl , 4-substituted benzaldehydes and ammonium acetate. The structures of MTCl and 1a-1g were characterized by FT-IR, 1 H NMR, 13 C NMR and mass spectrometry （MS）. Fluorescence analysis showed that the dilute solution of 1a - 1g in DMF （1×10 -5 mol/L） fluorescence emission wavelength was in the blue-green region of 439-554 nm. Comparing with 2-phenyl-4,5-di（4-chlorostyryl） imidazole （ 1e ）, when the 2-phenyl ring has a substituent, the fluorescence emission wavelength of 1a-1g is red shifted, however, the relative quantum yield decreases as the electron donating ability of the substituent on the 2-phenyl ring increases. It is noted that the cleavable group cyano does not affect the relative quantum yield. Acid-base effect test results showed that 2-（4-dimethylaminophenyl）-4,5-di（4-chlorostyryl） imidazole （ 1a ） was the most sensitive to acid, after 5μL of the sulfuric acid solution （0.03 mol/L） was added to a DMF diluted solution of 1a , the fluorescence intensity rapidly reached a minimum; 2-（4-cyanophenyl）-4,5-di（4-chlorostyryl） imidazole （ 1g ） was more sensitive to alkali, the fluorescence intensity of the solution almost disappeared when 5 μL of tetrabutylammonium hydroxide aqueous solution （TBAH, 2.0 wt%） was added to the DMF solution of 1g , and the fluorescence performance was restored after adding acid, therefore 1g had the acid/alkaline switching effect. While a small amount of TBAH was added to imidazole derivatives of 2-（4-methoxyphenyl）, 2-（4-hydroxyphenyl）, 2-（4-methylphenyl） and 2-phenyl groups, their “double” fluorescence emission peak intensity was reduced, and the fluorescence performance was restored after adding acid. The intensity of one of the “double” was reduced when a small amount of dilute sulfuric acid was added, and the other was enhanced, and the fluorescence performance was restored after adding of dilute alkali.