Design and Synthesis of a Caged Carboxylic Acid with a Donor-π-Donor Coumarin Structure: One-photon and Two-photon Uncaging Reactions Using Visible and Near-Infrared Lights.

A caged carboxylic acid with a novel two-photon (TP)-responsive donor-π-donor coumarin backbone with a quadrupolar nature was designed and synthesized in this study. The newly synthesized coumarin derivative showed a strong one-photon (OP) absorption band (ε ≈ 29000 cm-1 M-1) in the visible region (>∼400 nm). Time-dependent density functional theory calculations predicted a sizable TP absorption cross-section with a maximum at ∼650 nm significantly lager than that related to the OP absorption band. This is confirmed experimentally using TP excited fluorescence in the fs regime that leads to TP absorption cross-section of 18 and 5.6 GM at 680 and 760 nm, respectively. The OP photolysis (400 nm) and near-infrared-TP photolysis (750 nm) of the caged benzoic acid resulted in a clean formation of benzoic acid and an aldehyde.