Femtosecond fragmentation of tetraphenylhydrazine in solution

Abstract

The photo-induced dissociation of tetraphenylhydrazine (TPH) in alkane solutions is studied by femtosecond pump—probe spectroscopy and by fluorescence lifetime measurements. The absorption of the photoproduct, a pair of diphenylaminyl radicals, is found to rise with a time constant of 80 ± 25 fs. The excited-state lifetime of TPH in cyclohexane is measured to be 16 ps and found to be only slightly dependent on solvent viscosity. All our measurements and those of others can be explained by assuming the upper-state potential in TPH to be a double well. Fragmentation of TPH proceeds via two channels. First, the excited wave-packet branches ultrafast into a dissociative continuum and into a bound state. Subsequently, this bound state tunnels on a picosecond time scale into the dissociative channel as well.