偶氮Calixarenes的合成與其光與熱誘導異構化的研究

Abstract

偶氮化合物的熱與光誘導順反異構化現象已是眾所皆知，但在calixarene中則尚未被探討過，因此本論文中我們合成一系列偶氮化合物並從事光與熱誘導異構化的研究。首先我們研究在照光過程中紫外及可見光光譜在不同時間下之差異性，在我們的研究中發現下緣有烷氧取代的偶氮calix[4]arenes（26-27）的反式至順式的異構化速率常數（kt-c）會比下緣沒取代的偶氮calix[4]arenes（23-25）快6-35倍。接著也探討偶氮calix[4]arenes的溫度效應，由研究結果發現此類化合物照光後的順式結構在室溫下就會變回反式結構，原因推斷偶氮基團在calix[4]arene上的順式結構擁有較大的立體障礙。最後由阿瑞尼士方程式間接求得順反異構化的活化能（Eac-t），下緣沒取代的偶氮calix[4]arenes（25a與25c）活化能約為2 kcal/mol左右；下緣有取代的偶氮calix[4]arenes（26與27）則在11-17 kcal/mol之間。

Photo- and thermo- induced cis-trans isomerization of azo-compounds is well-known, however, related reports on the azo-calixarenes（23-27）has been few, thus in this work, a series of azo-calix[4]arenes were synthesized and their photo- and thermo- induced isomerization studied. Time dependent uv/vis spectra were taken for the azo-compounds under uv irradiation. Photoinduced cis to trans isomerization rates of these azo-compounds were determined from the uv/vis spectral data. We found that calix[4]arenes（26-27）with alkoxy substituent in the lower rim have larger kt→c than those without（i.e. compounds 23-25）. The activation energies of cis to trans azo-calix[4]arene were determined by studying temperature dependent cis to trans isomerization for these azo-calix[4]arenes . These values are about 2 kcal/mol for azo-calix[4]arenes 25a and 25c and are 11 to 17 kcal/mol for azo-calix[4]arenes 26 and 27.