Live-cell one- and two-photon uncaging of a far-red emitting acridinone fluorophore

Total synthesis and photophysical properties of PENB-DDAO, a photoactivatable 1,3-dichloro-9,9-dimethyl-9H-acridin-2(7)-one (DDAO) derivative of a far-red emitting fluorophore, are described. The photoremovable group of the DDAO phenolic function comprises a donor/acceptor biphenyl platform which allows an efficient (> or = 95%) and rapid (< 15 micros time-range) release of the fluorescent signal and displays remarkable two-photon uncaging cross sections (delta(a) x Phi(u) = 3.7 GM at 740 nm). PENB-DDAO is cell permeable as demonstrated by the triggering of cytoplasmic red fluorescent signal in HeLa cells after one-photon irradiation (lambda(exc) around 360 nm) or by the generation of a red fluorescent signal in a delineated area of a single cell after two-photon photoactivation (lambda(exc) = 770 nm).