INFRARED-SPECTRA OF TETRAMERIZED ORGANIC SEMICONDUCTORS PRPHT(TCNQ)(2) AND PRQUIN(TCNQ)(2) - THE PROBLEM OF A(G) PHONON MODE SPLITTING

Polarized infrared reflectance spectra from single crystals of two org anic charge-transfer salts PrPht(TCNQ)(2) and PrQuin( TCNQ)(2) (where TCNQ = tetracyano-p-quinodimethane, PrPht = N-propylphtalazinium, PrQu in = N-propylquinoxalinium) are studied over the frequency range 400-7 000 cm(-1) at room temperature (in both compounds the TCNQ molecules a re arranged to form linear stacks with the tetramer repeat unit). Kram ers-Kronig analysis of the reflectance is used to determine the optica l properties. Some vibrational lines related to the coupling of a(g) p honon modes of the TCNQ molecule with electrons are split. The origin of a(g) mode splitting is discussed. Moreover, the electronic spectra (up to 20 000 cm(-1)) are measured at room temperature using the KBr p ellet technique. The charge-transfer bands in tetramerized TCNQ salts are analysed.