Excitation energy transfer of a bichromophoric cross-shaped molecule investigated by polarized fluorescence spectroscopy

The excitation energy transfer (EET) of a bichromophoric cross-shaped molec ule was investigated by stationary polarized fluorescence spectroscopy in t he solid state. For this purpose 2,2',7,7'-tetrakis(biphenyl-4-yl)-9,9'-spi robifluorene was embedded in a polymeric bisphenol-A-polycarbonate (PC) mat rix. The dependence of the fluorescence on concentration and wavelength was determined. The role of the intermolecular and intramolecular EET is dealt with separately and discussed by means of the degree of polarization. The intermolecular excitation energy transfer is described in terms of a Forste r transfer mechanism. The intramolecular transfer is prevented for the zero -point vibrational levels by the molecular cross-shaped structure, but is f ound for a wide range of wavelength, presumably based on vibrationally exci ted states. (C) 2000 American Institute of Physics. [S0021-9606(00)50922-2] .