Theoretical study of push-pull molecules based on thiophene oligomers

摘要

Thiophene oligomers ($alpha@-$alpha$PRM linkages) have been intensively studied in past years. In particular, sexithiophenes have been synthesized with a high degree of purity and good crystallinity allowing the fabrication of reliable field effect transistors. When donor- acceptor terminal groups are attached to thiophene oligomers, an anomalous behavior of the fluorescence as a function of the number of rings has been reported. There are experimental evidences of charge transfer suppression for oligomers containing more than four rings. In this work, we investigate the electronic structure of these systems. Geometrical optimizations and spectroscopic features of both ground and excited states are obtained through the use of sophisticated semi-empirical methods. Our results show that charge transfer suppression can be explained in terms of the evolution of the electronic spectrum.