Scheme 2.

Mechanistic investigation. a) Reaction conducted in CD₃CN and DMF‐d⁶. b) 2 equiv D₂O was added. c) Formation of CsDCO₃ via direct or indirect H/D exchange with D₂O. d) Z/E‐isomerization via energy transfer using photocatalyst Pc4. e) CV measurement of Pc4. f) Steady‐state Stern–Volmer experiment of Pc4 and Boc‐Pro‐OCs (2 a+Cs₂CO₃). g) Phosphorescence lifetimes of ^3*Pc4 at different concentrations of quencher (2 a+Cs₂CO₃). h) Combined quenching data of steady‐state and time‐resolved studies of Pc4. i) Stern–Volmer analysis yielded a rate constant, k _ET, of (3.12±0.12)×10⁹ L mol⁻¹ s⁻¹ by the SET between ^3*Pc4 and Boc‐Pro‐OCs (2 a+Cs₂CO₃). The backward reaction rate is negligible. j) Steady‐state Stern–Volmer quenching analysis of Pc1 in the presence of Boc‐Pro‐OCs (2 a+Cs₂CO₃), phenylacetylene 1 a or p‐bromoacetophenone 5 i.