Singlet and Triplet Contributions to the Excited-State Activities of Dihydrophenazine, Phenoxazine, and Phenothiazine Organocatalysts Used in Atom Transfer Radical Polymerization

The photochemical dynamics of three classes organic photoredox catalysts employed in organocatalyzed atom-transfer radical polymerization (O-ATRP) are studied using time-resolved optical transient absorption and fluorescence spectroscopy. nine selected for study examples N-aryl core-substituted dihydrophenazine, phenoxazine phenothiazine compounds with varying propensities control outcomes. Excited singlet-state lifetimes extracted from the spectroscopic measurements reported N,N-dimethylformamide (DMF), dichloromethane (DCM), toluene. Ultrafast (<200 fs to 3 ps) electronic relaxation photocatalysts after photoexcitation at near-UV wavelengths (318–390 nm) populates first singlet excited state (S1). S1-state range 130 ps 40 ns a considerable dependence on photocatalyst structure solvent. competition between ground recovery intersystem crossing controls triplet populations is minor pathway dihydrophenazine derivatives but greater importance catalysts. A comparison our results previously O-ATRP performances various shows that high triplet-state quantum yields not prerequisite controlling polymer dispersity. For example, 5,10-bis(4-cyanophenyl)-5,10-dihydrophenazine, shown exert good control, possesses shortest lifetime (135 DMF 180 N,N-dimethylacetamide) among here negligible yield. call re-evaluation excited-state properties most significance governing photocatalytic behavior reactions.