Vibrational spectra of two new organic semiconductors: tetrathiafulvalene (TTF) and tetramethyltetraselenafulvalene (TMTSF) salts of paranitrophenylmalononitrile (PNMA)

Abstract

Two new complexes of stoichiometry 2:1 are reported for the donors tetrathiafulvalene (TTF) and tetramethyltetraselenafulvalene (TMTSF) with the acceptor paranitrophenylmalononitrile (PNPMA). Both compounds are semiconductors with a resistivity of about 4 × 10−4 Ω m for (TMTSF)2PNPMA and 0.58 Ω m for (TTF)2PNPMA. The larger conductivity of the first complex can be attributed to the disorder of the PNPMA anions. Vibrational spectra were obtained by FTIR and Raman spectroscopy, in order to determine the degree of charge transfer in these systems. Both complexes have the electron distribution (D+0.4)2A−0.8. As a result the donors D stack in tetramerized units and exhibit vibronic activation of certain symmetric monomer modes, thus indicating the presence of strong electron–vibrational interactions in the donor stacks. Key words: TTF and TMTSF salts, charge transfer complexes, IR and Raman spectra, degree of charge transfer, paranitrophenylmalononitrile (PNPMA).