Electron-molecular vibration coupling in trimerized isostructural mixed-stack complexes (EDT-TTF-I)TCNQF (n = 0, 1, 2).

Infrared and Raman spectra of three isostructural charge transfer complexes (EDT-TTF-I)TCNQF (n = 0, 1, 2) are studied. The planar molecules in these complexes are arranged in one-dimensional stacks formed by donor-acceptor-donor (DAD) centrosymmetric trimeric units with a different degree of charge transfer between D and A. In the IR electronic spectra two bands attributed to D → D and D → A charge transfer transitions are distinguished. In the IR vibrational spectra, numerous bands related to coupling of D and A intramolecular vibrations with electrons, are seen. The electron-molecular vibration coupling is clearly seen for acceptor modes attributed to CN, CC stretching, and CH bending as well as for CC stretching donor modes. These modes are investigated as a function of temperature (T = 300-10 K). The temperature effect is especially significant for the n = 1 complex which undergoes a neutral-to-ionic phase transition. In our study we show that the electron-molecular vibration coupling has also an influence on Raman spectra.