Evidence for the coexistence of two different mechanisms for the occurrence of anti-Kasha S2 (1 1Bu) fluorescence from α- ω diphenylpolyenes

Itoh Takao

Journal of Chemical Physics

Fluorescence, fluorescence excitation, and absorption spectra have been measured for diphenylpolyenes with the polyene double bond number (n) from three to seven in solvents with different polarizabilities at room temperature. These polyenes exhibit anti-Kasha S2 (1 1Bu) fluorescence beside conventional S1 (2 1Ag) fluorescence in room temperature solution. It is shown that there are two different mechanisms for occurrence of the S2 (1 1Bu) fluorescence of diphenylpolyenes. S2 fluorescence occurs through the thermal population of the S1 state for the shorter diphenylpolyenes (n = 3 and 4), while it occurs as prompt S2 fluorescence due to inefficient S2-->S1 internal conversion for the longer diphenylpolyenes (n = 6 and 7). With diphenyldecapentaene (n = 5), S2 fluorescence based on both mechanisms is observed depending on the polarizability of the solvent used. The present results provide deeper insight into the mechanism for the occurrence of anti-Kasha S2 fluorescence of polyenes.

Physics [ 420 ]

eng

American Institute of Physics

Copyright (c) 2004 American Institute of Physics

[NCID] AA00694991

[ISSN] 0021-9606

[DOI] 10.1063/1.1791155

[DOI] http://dx.doi.org/10.1063/1.1791155