Transient excited-state absorption of the liquid crystal CB15 [4-(2-methylbutyl)-4-cyanobiphenyl] in its isotropic phase

Abstract

Abstract Liquid crystals are known to possess large electronic optical non-linearities. Transient photoinduced absorption is not commonly applied to liquid crystals, but it is a powerful technique by which to examine the excited-state absorption (ESA) and hence the non-linear absorption of molecular systems. We show that measurements of this kind can give an insight into the dominant mechanisms of picosecond non-linear optical response in liquid crystals, and together with semi-empirical quantum chemical calculations appropriate assignments of the absorptions can be made. In particular, we report measurements of the transient ESA of the liquid crystal CB15 [4-(2-methylbutyl)-4-cyanobiphenyl] in its isotropic phase using femtosecond pump-probe spectroscopy in the wavelength range from 400 to 1000 nm. By pumping directly into the first excited state (S1) we identify at least four transient ESAs which contribute to the non-linear response up to a time of 1 ns after excitation. These features show a linear de...