Ultrafast dynamics of photoexcited trans-1,3,5-hexatriene in solution by femtosecond transient absorption spectroscopy

We have investigated the ultrafast dynamics of trans-1,3,5-hexatriene in cyclohexane and acetonitrile solutions following photoexcitation to the 1 1Bu state. The transient absorption in the visible region consists of an instantaneous rise (< 150 fs) and decay in less than 500 fs, whose time constant depends on the probe wavelength. The bleach recovery at 268 nm indicates that the vibrational relaxation in the ground state occurs in 15–20 ps, followed by a subnanosecond relaxation.