Time-resolved photoisomerization of 1,1′-di-tert-butylstilbene and 1,1′-dicyanostilbene

Abstract Photoisomerization of 1,1′-di-tert-butylstilbene ( 3 ) and 1,1′-dicyanostilbene ( 4 ) is monitored with stationary and broadband transient absorption spectroscopy. The electron affinity of the substituents correlates with the shift of the absorption band. The weak extinction of 3 complicates data interpretation, but comparison with earlier measured 1,1′-dimethylstilbene ( 1 ) and 1,1′-diethylstilbene ( 2 ) helps to assign transient spectra and relaxation paths. For 3 a long-lived perpendicular state P is observed with lifetime τ P  = 134 ps in acetonitrile. For 4 τ P  = 2.1 ps in acetonitrile and 27 ps in n-hexane, the difference indicating a substantial dipole moment (∼3D) of the …