Sensitized Two-Photon Activation of Coumarin Photocages.

Here we report the design of a new coumarin-based photolabile protecting group with enhanced two-photon absorption. Two-photon excited fluorescence (TPEF), color-tuned ultrafast transient absorption spectroscopy and infrared (IR) measurements are employed to photochemically characterize the newly designed ATTO 390-DEACM-cargo triad. Increased two-photon cross-section values of the novel cage in comparison to the widely used protecting group DEACM ([7-(diethylamino)coumarin-4-yl]methyl) are extracted from TPEF experiments. Femtosecond pump-probe experiments reveal a fast intramolecular charge transfer, a finding that is confirmed by quantum chemical calculations. Uncaging of glutamate is monitored in IR measurements by photodecarboxylation of the carbamate linker between the photolabile protecting group and the glutamate, showing the full functionality of the novel two-photon activatable photocage.