Silk-Derived Photoelectrode Enables Sustainable Benzylic Etherification via Photoelectrocatalysis

We present a sustainable photoelectrochemical platform based on a silk-based photoelectrode functionalized with phenothiazine (PTZ). The PTZ–silk system enables selective benzylic C–H etherification under mild conditions. Structural and electrochemical characterization confirmed successful PTZ functionalization and an anodic half-wave potential ( E 1/2 = +1.09 V vs SSCE). The photoelectrochemical reactions deliver isolated yields of up to 89% (diphenylmethane) and can be recycled for 10 consecutive runs. Postcycling FT-IR supports operational stability, showing retention of key PTZ features with a gradual attenuation consistent with minor loss of surface-bound PTZ. Mechanistic experiments are consistent with a PTZ-mediated, photoinduced single-electron transfer pathway. This work demonstrates the potential of bioderived, heterogeneous catalysts for sustainable organic synthesis.