Charge-Transfer Controlled Crystallization of a Model Oligomer for Donor-Acceptor-Polythiophenes

A model donor-acceptor oligomer consisting of benzodithiophene-diketone and thiophene has been investigated with regard to its molecular packing and opto-electronic properties. The crystal structure suggests that the packing is dominated by charge-transfer interactions between the electron-rich part of the molecule and the electron-poor part. A series of observations corroborate this assumption, among them are a charge-transfer band in the film absorption spectra and exceptionally low π-π distances. A detailed analysis of the energetic levels of the present system reveals that only the HOMO level of the acceptor is shifted by conjugation to the donor. The results can contribute to the development of improved materials for organic electronics.