Photophysical characterization of 2,9-bis(7-benzothiazole-9,9′-didecylfluoren-2-yl)perylene diimide:: a new standard for steady-state fluorescence anisotropy

The absorption, fluorescence excitation and emission spectra have been obtained in solution for 2,9-bis(7-benzothiazole-9,9-didecyl-fluoren-2-yl)perylene diimide. Efficient resonance energy transfer from the fluorenyl group to the perylene ring center was observed. Interestingly, fluorescence emission was detected from the second excited electronic state of the perylene ring system. Fluorescence excitation anisotropy spectra obtained at room temperature exhibited a parallel orientation of the main absorption and emission band transition moments for the perylene-based dye in CH2Cl2. The value of excitation fluorescence anisotropy for the perylene dye in solution approached the theoretical maximum limit (r approximate to 0.4), and indicated that the rotational correlation time exceeded the lifetime of the first excited state. These results provide the basis for using this unique compound as an anisotropy reference standard. (C) 2002 Elsevier Science B.V. All rights reserved.