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The temperature dependence of the absorption spectra of 2,2 0 -bithiophene and 2,2 0 :5 0 ,2 00 -terthiophene isolated molecules in cyclodextrin (CyD) were investigated between 15 K to room temperature (RT). The optical absorption spectra of BT molecules inand -CyD, (BT) -CyD and (BT) -CyD are nearly the same between 15 K and RT. Those of TT are almost the same for (TT) -CyD and (TT) -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.

Highly purified single crystals of pyrene were made by a gas phase crystal growth method from 180 times of zone-refined pyrene. The dry powder of -cyclodextrin including a pyrene single molecule and that of -cyclodextrin including twin molecules were prepared under vacuum. The luminescence spectra of pyrene single molecules, twin molecules and single crystals, and their temperature dependences were measured with great care in the process of cooling the samples. It is found that the features of luminescence spectra at 2 K are quite different from each other. Pyrene twin molecules in -cyclodextrin show an excimer luminescence similar to that of single crystal. The vibronic luminescence in the range of 3.0 -3.5 eV comes from the ground-excited-state complex, or in other words, from the vibronic exciton, in contrast to the hitherto-assigned luminescence from another type of selftrapped exciton or metastable B-state which is the precursor of selftrapped excitons.