BAND-SHAPE ANALYSIS OF THE CHARGE-TRANSFER FLUORESCENCE IN BARRELENE-BASED ELECTRON DONOR-ACCEPTOR COMPOUNDS

In this paper we analyze the band shapes of the stationary fluorescenc e spectra for the radiative charge transfer recombination D+-A(-)--> D -A + hv in a series of barrelene-based organic bridged donor (D)-accep tor (A) molecules D-A, exploring solvent polarity and temperature effe cts on the band shape. Free energy changes for charge recombination, m edium reorganization energies, and intramolecular reorganization energ ies (for high- and medium-frequency vibrational modes) were evaluated from the band maximum energies and the full widths at half-maximum and from the fits of standard Franck-Condon factors to the entire fluores cence band shape. Utilization of a single high-frequency intramolecula r model (h omega(i) = 1300 cm(-1)) in conjunction with solvent modes p rovided a satisfactory fit of the band shape; however, such an analysi s results in unphysically large medium reorganization energies for non polar solvents (0.30-0.45 eV) and their large temperature dependence. The inclusion of medium-frequency (h omega similar to 500 cm(-1)) intr amolecular modes in the band-shape analysis is important for the prope r distinction between solvent and intramolecular reorganization.