二苯乙烯胺之分子內電荷轉移行為與螢光感應之研究

Abstract

本篇論文主要是利用具扭轉型分子內電荷轉移(TICT)行為之二苯乙烯胺做為離子螢光感應材料之研究。本實驗室先前發現反式-4-(N-甲氧苯基)二苯乙烯胺1OM在極性溶液中，其分子內電荷轉移激發態會進行扭轉而產生TICT態，使得螢光量子產率大為降低。欲進一步應用於金屬離子感應材料的設計，我們合成了一系列具腙取代基的反式-4-(N-甲氧苯基)二苯乙烯胺的衍生物1Hz、2Hz、3Hz，因為文獻報導腙官能基對銅有極高的選擇性。我們預期此類化合物與銅離子結合後會減弱甲氧基的電子供給能力，並抑制扭轉分子內電荷轉移的形成，進而提高螢光的強度，產生off-on的螢光感應行為。結果證明此類化合物在乙腈溶液中對於銅離子具有選擇性，亦即只有在銅離子存在下，感應分子的螢光才有變化，螢光強度在兩當量銅離子的情況下，其變化量為2Hz > 1Hz > 3Hz 。然而，進一步比較不具腙取代基的類似化合物感應行為，顯示胺基的氮原子才是主要與銅離子作用的部分，而非官能基腙，因此，文獻所報導之感應行為有必要進一步釐清。 除此之外，為了探討延長共軛系統對於TICT的影響，我們在1OM的不同位置上分別接上苯基，亦即化合物4OM與3OM 。結果顯示在極性溶液中兩者的螢光量子產率皆比1OM高，表示TICT的行為受到了部分抑制，其中尤以3OM在二氯甲烷中的螢光量子產率更高達0.95，比1OM的螢光量子產率高出許多，顯示此化合物在二氯甲烷中的TICT激發態可以被忽略。

This thesis is mainly a study on aminostilbene-based fluoroionophores with character of twisted intramolecular charge transfer（TICT）. Our previous research has shown that trans-(N-(4-methoxylphenyl)amino)stilbene（1OM）forms a TICT state upon electronic excitation by twisting the C-N bond and thus possesses low fluorescence quantum yields. We have taken the advantage of this TICT behavior for the design of new fluoroionophores and synthesized a series of trans-4-(N-arylamino)stilbenes containing a hydrazone substituent, namely 1Hz、2Hz and 3Hz. According to literatures, the hydrazone and methoxyl groups can selectively interact with Cu2+ ion. We except that the electron donating ability of the methoxy group will decrease upon binding with Cu2+, which would inhibit the formation of TICT and result in an enhancement of fluorescence intensity and an off-on fluoroionophoric behavior. The results indeed show that the fluorescence of 1Hz、2Hz and 3Hz only respond to the present of Cu2+ in acetonitrile solution, and the magnitude of fluorescence response is 2Hz > 1Hz > 3Hz. However, similar fluoroionophoric behavior is also observed for compounds without the hydrazone group, revealing that the amino nitrogen atom rather than the hydrazone group is responsible for interactions with Cu2+. Thus, the interpretation of fluoroionophoric behavior in the literature needs to be reexamined. We have also investigated the effect of π-conjugated length on the TICT behavior of aminostilbenes by adding a phenyl group to different positions of 1OM（i.e. 3OM and 4OM）. The results show that both 3OM and 4OM posses higher fluorescence quantum yield than 1OM, indicating that the TICT character is largely suppressed. In particular, compound 3OM has a fluorescence quantum yield as large as 0.95 in dichloromethane, which indicate that the TICT formation is unimportant for 3OM in dichloromethane.