Solvent Effects on Exciplex Conformation between Planar and Twisted Charge Transfer Complexes

Abstract

Exciplex is an excited complex of electron donor and acceptor after photo-induced electron transfer (PET) between them. It has been studied in very detail for more than a half decade because it is a common transient species through PET phenomena in fields including organic pigments, chemical sensors, chemical magneto-indicators, organic light-emitting diodes, and organic photovoltaic cells. One of the characteristics of the exciplex is red shift of its emission band with increasing solvent polarity. This can be understood that the excited electronic state of charged complex (i.e., exciplex) becomes more stable in polar solvent. [1] In this study we observed the solvent polarity effect on exciplex emission of a tethered electron donor – acceptor system, pyrene-(CH2)12-O-(CH2)2-N,N-dimethylaniline (Py-12-O-2-DMA). Moreover, we mimicked the polar solvent effect in a nonpolar solvent, hexane by introducing an electron withdrawing group to the pyrene, pyrene-COO-(CH2)11-O-(CH2)2-N,N-dimethylaniline (Py-COO-11-O-2-DMA). We compare emissions from Py-12-O-2-DMA and Py-COO-11-O-2-DMA in hexane and propose that the features captured provide useful information about conformations of the excited charged complexes and it is supported by density functional theory calculation.