TRANSIENT ABSORPTION-SPECTRA AND BLEACHING OF 4'-N-PENTYL-4-CYANOTERPHENYL IN CYCLOHEXANE - DETERMINATION OF CROSS-SECTIONS AND RECOVERY TIMES

We investigated the excited state absorption (ESA) of 5CT (4'-n-pentyl -4-cyanoterphenyl) dissolved in cyclohexane in the wavelength range fr om 400 to 870 nm. Time resolved measurements of these transient absorp tions were used for the differentiation between singlet and tripler ab sorption. We detected a long living component, which could be related to a tripler band centered at 500 nm and 55 nm broad (FWHM) and a shor t living absorption indicating a S-1-->S-n-transition band centered at 576 nm with a width of 16 nm (FWHM). The life time of the tripler sta te was determined to be (340+/-5) ns for the not-degassed sample. Meas urements of the ground state depopulation and the fluorescence as a fu nction of the excitation intensity were modeled using rate equations. Thus we were able to determine the population densities of the relevan t excited states and the cross section for the S-1-->S-n absorption. F inally, the relaxation time of the higher excited electronic singlet s tate S-n to the first excited singlet S-1 was estimated to 0.5 ns from bleaching of this transient absorption. (C) 1996 American Institute o f Physics.