反式二苯乙烯胺激發態結構異構化行為之研究

Abstract

對於許多共軛分子來說，激發態結構異構化是一個非常重要的非放光去活化路徑。反式二苯乙烯胺特別之處於在單重激發態時可同時擁有雙鍵扭轉(順反異構化)及單鍵扭轉(扭轉分子內電荷轉移)兩種去活化模式。在這篇論文裡，我們從三種層面來探討不同因素對於激發態單雙鍵扭轉的影響，包括了構形效應、位置效應及硝基取代效應。首先，以具有扭轉分子內電荷轉移行為的化合物p1CN為參考模型，我們研究了基態的構形差異對於激發態行為的影響。基於對一系列臨位取代二苯乙烯胺o1R與o2的研究，再與其對位與間位異構物的性質做比較，我們也針對取代基的位置效應歸納出一個很完整的概念。除此之外，從分子DNS與其多架橋取代模型-DNSB3極為相似的激發態性質我們可以確切地指出DNS的扭轉分子內電荷轉移的位置在硝基與二苯乙烯胺之間的單鍵。最後，於己烷溶液中，對於胺基上甲基與苯基取代造成硝基二苯乙烯胺量子產率的差異也進行了深入的討論。

Excited-state structural isomerization about a specific bond is an important nonradiative decay channel for many π-conjugated systems. trans-Aminostilbenes are unique as donor-acceptor molecules that could undergo both double bond torsion (trans →cis isomerization) and single bond torsion (twisted intramolecular charge transfer, TICT) in the singlet excited state. In this thesis, we investigated the excited-state bond torsion of aminostilbenes in terms of several aspects, including conformational, positional and nitro substitution effect. First, the ground-state conformation effect on the excited-state behavior has been given by using p1CN, a TICT-possessing compound, as reference. A series of trans-2-(N-arylamino)stilbenes (o1R and o2) have been studied and a complete picture of position effect was obtained in conjunction with the properties of the para and meta isomers. Furthermore, we provided an unambiguous conclusion that nitro group is responsible for the twisting in TICT state for DNS based on the similarity of excited-state behavior between DNS and a multi-site constrained model, DNSB3. Finally, the N-methyl and N-phenyl effect on the excited-state quantum yields of aminonitrostilbenes in hexane was also discussed.