Interrogation of O-ATRP Activation Conducted by Singlet and Triplet Excited States of Phenoxazine Photocatalysts

Abstract

Organocatalyzed ATRP (O-ATRP) is a growing field exploiting organic chromophores as photoredox catalysts (PCs) that engage in dissociative electron transfer (DET) activation of alkyl halide initiators following absorption of light. Characterizing DET rate coefficients (k act ) and photochemical yields across various reaction conditions and PC photophysical properties will inform catalyst design and efficient use during polymerization. The studies described herein consider a class of phenoxazine PCs where synthetic handles of core-substitution and N-aryl substitution enable tunability of the electronic and spin character of the catalyst excited state as well as DET reaction driving force ( ). Using Stern-Volmer quenching experiments through variation of diethyl 2-bromo-2-methylmalonate (DBMM) initiator concentration, collisional quenching is

Structure-Dependent Electron Transfer Rates for Dihydrophenazine, Phenoxazine, and Phenothiazine Photoredox Catalysts Employed in Atom Transfer Radical Polymerization

“…It is the more exothermic Δ G ET values that result in small (1–2 kJ/mol) activation energies for ET from the LE catalysts, which in turn lead to the values of k ET being close to the estimated diffusional rate coefficients for DMF at 20 °C. Therefore, Δ G ET can be classified as one of the most important factors in the design of such PCs for ATRP, an argument which was also developed in our prior publications. ,, A recent study by Damrauer and co-workers of four phenoxazine based PCs adopts a similar argument …”

“…35,36,44 A recent study by Damrauer and co-workers of four phenoxazine based PCs adopts a similar argument. 56…”

Phenoxazine‐Sensitized CO2‐to‐CO Reduction with an Iron Porphyrin Catalyst: A Redox Properties‐Catalytic Performance Study

“…Note that this experiment likely probes the singlet excited state of the organic Phen derivatives because they are typically not phosphorescent in solution at ambient temperature. However, reactivity from both the singlet and triplet excited states of phenoxazines are relevant in catalysis and provide insight into the reactivity [33] . All six Phen derivatives possess an absorption in the visible domain (Figure S1) with extinction coefficients at the 400 nm lower threshold ranging from 8.4×10 3 to 3.1×10 4 (Table S1).…”

“…However, reactivity from both the singlet and triplet excited states of phenoxazines are relevant in catalysis and provide insight into the reactivity. [33] All six Phen derivatives possess an absorption in the visible domain (Figure S1) with extinction coefficients at the 400 nm lower threshold ranging from 8.4 × 10 3 to 3.1 × 10 4 (Table S1). For all six Phen derivatives, a clear emission decay was observed in the presence of increasing amount of FepTMA catalyst.…”

Effects of the Chalcogenide Identity in N‐Aryl Phenochalcogenazine Photoredox Catalysts

“…Following early O‐ATRP reports, the superior catalytic properties of 10‐phenyl phenothiazine [6] over perylene [10] motivated the development of new phenochalcogenazine PCs, including numerous phenothiazines [11,12] and phenoxazines [7,13,14] . In particular, significant research efforts were devoted to tuning the yield of PC triplet excited states ( 3 PC*), [7,12,15,16] which may benefit catalysis due to their longer lifetimes than singlet excited states ( 1 PC*) by making them more likely to engage in catalysis [17–19] . It has been hypothesized that tuning the identity of the chalcogenide in these PCs could serve as a useful strategy for increasing the yield of 3 PC*.…”