Abstract
Using trianisole heptazine (TAHz) as a monomeric analogue for carbon nitride, we performed ultrafast pump-photolysis-probe transient absorption (TA) spectroscopy on the intermediate TAHzH(•) heptazinyl radical produced from an excited state PCET reaction with 4-methoxyphenol (MeOPhOH). Our results demonstrate an optically gated photolysis that releases H(•) and regenerates ground state TAHz. The TAHzH(•) radical signature at 520 nm had a lifetime of 7.0 ps, and its photodissociation by the photolysis pulse is clearly demonstrated by the ground state bleach recovery of the closed-shell neutral TAHz. This behavior has been previously predicted as evidence of a dissociative πσ* state. For the first time, we experimentally demonstrate photolysis of the TAHzH(•) heptazinyl radical through a repulsive πσ* state. This is a critical feature of the proposed reaction mechanisms involving water oxidation and CO(2) reduction.