INHOMOGENEITY OF THE LUMINESCENCE ANISOTROPY SPECTRUM OF J-AGGREGATESWITH 2 MOLECULES PER A UNIT-CELL

The structure of the luminescence anisotropy spectrum of J-aggregates of a thiocarbocyanine dye isulfopropyl-5,5'-dichloro-9-ethylthiacarbox yanine (THIATS), revealing the Davydov splitting of the exciton band, is studied at different (including anti-Stokes) excitation wavelengths . Upon excitation of luminescence at the upper Davydov component in ab sorption, the luminescence anisotropy varies from +0.07 at the half-ma ximum to -0.1 at the center of the luminescence band. The efficient al ignment of aggregates in the liquid how in a rotating cell and an infl uence of this alignment on the luminescence anisotropy spectrum are fo und. The relationship between these results and the microscopic and ma croscopic structure of J-aggregates is discussed.