Ultrafast dynamics of sterically hindered tetraphenylmethylbutadiene in liquids

Ultrafast transient dynamics of photoexcited tetraphenylmethylbutadiene (TPMB) were measured as a function of probe wavelength and solvent viscosity. In contrast to diphenylbutadiene, which undergoes simple isomerization dynamics, and tetraphenylbutadiene, which exhibits a viscosity-independent transient absorption, TPMB undergoes complex spectral dynamics with distinctly different time constants and viscosity dependence. Results at different probe wavelengths provide evidence for at least two molecular photoisomerization channels and also suggest that the distribution of ground state conformations may be viscosity dependent. The rich dynamics of TPMB demonstrate the dramatic changes induced by the steric effect of the methyl group and the sensitivity of the potential energy surfaces to molecular geometry and solvent environment.