Two-photon sensitive protecting groups operating intramolecular electron transfer: uncaging of GABA and tryptophan.

Improved photo-labile protecting groups, with high sensitivity to two-photon excitation, are needed for the controlled release of drugs, as tools in neuroscience and physiology. Here we present a new modular approach to the design of caging groups based on photoinduced electron transfer from an electron-rich two-photon dye to an electron acceptor, followed by scission of an ester to release a carboxylic acid. Three different electron acceptors were tested: nitrobenzyl, phenacyl and pyridinium.

Thiophene-based dyes for probing membranes.

We report the synthesis of four new cationic dipolar push–pull dyes, together with an evaluation of their photophysical and photobiological characteristics pertinent to imaging membranes by fluorescence and second harmonic generation (SHG). All four dyes consist of an N,N-diethylaniline electron-donor conjugated to a pyridinium electron-acceptor via a thiophene bridge, with either vinylene (–CH=CH–) or ethynylene (–C≡C–) linking groups, and with either singly-charged or doubly-charged pyridinium terminals. The absorption and fluorescence behavior of these dyes were compared to a commercially available fluorescent membrane stain, the styryl dye FM4-64.

Model dyads for 2PA uncaging of a protecting group via photoinduced electron transfer.

Three dyads with a fluorene derivative as an electron-donor and with electron-acceptors of variable redox potentials were synthesized as models for two-photon activated uncaging via electron transfer. A spectroscopic and photophysical study of the component units and the dyads in solvents of different polarities demonstrated an efficient electron transfer (efficiencies > 80%) followed by charge recombination in the arrays (30 ps < τ < 1.6 ns).