Vibrational analysis of the inelastic neutron ascattering spectra of electron donor-acceptor complexes. II. Tetracyanoethylene-perylene by electronic structure calculations

The vibrational spectra of the electron donor-acceptor complex, tetracyanoethylene-perylene were measured at 4 K by inelastic neutron scattering (INS) using the filter analyzer neutron spectrometer (FANS) and at 20 K using the TOSCA instrument. A direct comparison of the measured spectrum was made to density functional calculations using the B3LYP/6-31G** treatment for the isolated complex, the PW91 pseudopotential plus plane-wave basis and the BLYP/dnd atom-centered basis solid-state methods. In general, comparisons of the observed and simulated spectra revealed that the PW91 method is slightly superior to the B3LYP/6-31G** and BLYP/dnd methods in predicting both vibrational frequency and intensity above 200 cm^-1. Below 200 cm^-1, the BLYP/dnd calculations gave slightly better intensity agreement. Six intermolecular vibrations were theoretically predicted with the three calculation methods and were experimentally confirmed. In addition, the molecular motions of the vibrations observed in the INS spectrum were tentatively assigned. Our calculations show that solid-state calculations are not required, at least in the case of the TCNE-perylene complex, to obtain reasonably accurate vibrational frequency information of electron donor-acceptor complexes.