Transient absorption spectra and bleaching of 4′-n-pentyl-4-cyanoterphenyl in cyclohexane — determination of cross sections and recovery times

Abstract

We investigated the excited state absorption (ESA) of 5CT (4′-n-pentyl-4-cyanoterphenyl) dissolved in cyclohexane in the wavelength range from 400 to 870 nm. Time resolved measurements of these transient absorptions were used for the differentiation between singlet and triplet absorption. We detected a long living component, which could be related to a triplet band centered at 500 nm and 55 nm broad (FWHM) and a short living absorption indicating a S1→Sn-transition band centered at 576 nm with a width of 16 nm (FWHM). The life time of the triplet state was determined to be (340±5) ns for the not-degassed sample. Measurements of the ground state depopulation and the fluorescence as a function of the excitation intensity were modeled using rate equations. Thus we were able to determine the population densities of the relevant excited states and the cross section for the S1→Sn absorption. Finally, the relaxation time of the higher excited electronic singlet state Sn to the first excited singlet S1 was estimated to 0.5 ns from bleaching of this transient absorption.