Temperature Dependence of the Absorption Spectra of Bithiophene and Terthiophene Isolated Molecules in Cyclodextrin

Abstract

The temperature dependence of the absorption spectra of 2,2'-bithiophene and 2,2':5',2''-terthiophene isolated molecules in cyclodextrin (CyD) were investigated between 15 K to room temperature (RT). The optical absorption spectra of BT molecules in β- and γ-CyD, (BT) β-CyD and (BT) γ-CyD are nearly the same between 15 K and RT. Those of TT are almost the same for (TT) β-CyD and (TT) γ-CyD . Anomalous temperature dependence of the absorption intensities was observed. The absorption intensities of the isolated molecules of BT and TT in CyD, (BT) CyD and (TT) CyD increase with increasing temperatures. The s-trans states of (BT) CyD and (TT) CyD convert to the s-cis states at high temperatures through the rotational vibration around the single bond between thiophene rings. The allowed transition of the s-cis conformation would mix to the forbidden transition of s-trans conformation, thus the absorption intensity increases at high temperatures.