Rhodamine-Sensitized Two-Photon Activation of a Red Light-Absorbing BODIPY Photocage.

Two-photon (2P) activatable probes are of high value in biological and medical chemistry since near infrared (NIR) light can penetrate deeply even in blood-perfused tissue and due to the intrinsic three-dimensional activation properties. Designing two-photon chromophores is challenging. However, the two-photon absorption qualities of a photocage can be improved with an intramolecular sensitizer, which transfers the absorbed light onto the cage. We herein present the synthesis and photophysical characterization of a 2P-sensitive uncaging dyad based on rhodamine 101 as donor fluorophore and a redshifted BODIPY as acceptor photocage. Liberation of p-nitroaniline (PNA) upon one-photon photolysis was confirmed by HPLC analysis. The photoreaction was found to be accompanied by a considerable change of the fluorescence properties of the chromophores. The possibility of a fluorescent read-out enabled the detection of two-photon induced uncaging by confocal fluorescence microscopy.