| 摘要: | 本篇論文為設計含有N-芳基取代基對二苯乙烯胺化合物(1c, 1d, 1f)，及N,N-二芳基取代之對二苯乙烯胺(1e)，與已知螢光微弱之對二苯乙烯胺化合物(1a, 1b)，作一系列的光化學性質的研究與比較。 結果顯示，N-芳基取代導致於4-位置的二苯乙烯胺之胺基部份的氮原子構形，趨於平面，並增加其共軛性質，造成吸收光譜與螢光光譜有著明顯之紅位移現象。同樣的，N-芳基取代對於4-位置的二苯乙烯胺分子於螢光激發態時，其中心雙鍵扭曲的較少，並增加分子的電荷轉移性質。因此，含N-芳基取代的化合物1c-1e與二苯乙烯胺化合物1a，1b及過去所報導過的單一取代之二苯乙烯相比較，其在室溫中有著高螢光量子產率和低異構化量子產率的特性。含N-芳基取代的化合物1c和1d是經由單重態進行異構化行為，而化合物1e則是經由三重態進行異構化行為，我們推論是其單重態有著極高的雙鍵扭轉能障的存在所造成。含N-芳基取代化合物1f相較於其他N-芳基取代化合物1c-1e而言，其激發態行為較類似於化合物1a，1b，我們推論這結果，是化合物1f的胺基構形平面性差，造成N-芳基取代和二苯乙烯胺之間的軌域重疊變差。N-芳基取代效應對於化合物2，3，4和5的結果與化合物1是相類似，所以N-芳基取代效應對於一般的二苯乙烯系統的影響是一普遍的現象，這種現象我們稱之為”胺基-共軛效應”。 The synthesis, structure, and photochemical behavior of the trans isomers of 4-(N-phenylamino)stilbene (1c), 4-(N-methyl-N-phenylamino)stilbene (1d), 4-(N,N-diphenylamino)stilbene (1e), and 4-(N-(2,6-dimethylphenyl) amino)stilbene (1f) are reported and compared to that of 4-aminostilbene (1a) and 4-N,N-dimethylaminostilbene (1b). The introduction of N-phenyl substituents to 4-aminostilbenes leads to a more planar geometry about the nitrogen atom, a red shift of the absorption and fluorescence spectra, and a less distorted central double bond and a larger charge-transfer character in the fluorescent state. Consequently, the N-phenyl derivatives 1c-1e have low photoisomerization quantum yields and high fluorescence quantum yields at room temperature, which is contrast to 1a, 1b, and any other previously reported unconstrained 4-monosubstituted trans-stilbenes. The isomerization of 1c and 1d is a singlet-state process, whereas it is a triplet-state process for 1e, presumably due to a higher singlet-state torsional barrier. The excited state behavior of 1f resembles 1a and 1b instead of 1c-1e as a consequence of the less planar amine geometry and weaker orbital interactions between the N-phenyl and the aminostilbene groups. Such an N-phenyl substituent effect is also found for 2 , 3 , 4 and 5 and appears to be general for other stilbenoid systems. The nature of this effect can be described as the “amino-conjugation effect”. |
