Unravelling the ultrafast photodecomposition mechanism of dibenzoyl peroxide in solution by time-resolved IR spectroscopy

Abstract

The ultrafast photo-fragmentation of dibenzoyl peroxide (DBPO) is studied using femtosecond UV excitation at 266 nm and mid-infrared broadband probe pulses to elucidate the dissociation mechanism. With the help of ¹³C-labeled DBPO it was possible to unambiguously assign transient IR bands in the fingerprint region to the benzoyloxy radical. Our experiments show that the fragmentation is controlled by the S₁-lifetime of DBPO and within 0.4 ± 0.2 ps leads to a benzoyloxy/phenyl radical pair plus CO₂via concerted bond breakage of the O–O and the phenyl–C(carbonyl) bond. 20% of the radical pairs geminately recombine to phenyl benzoate on a timescale of 70 ps.