The fluorescence of caged phthalimide-serine couples 2 and 4 is up/down modulated by decarboxylative photorelease with fluorescence decrease (2) vs. moderate fluorescence increase (4) serving as reporter function.
The chiral chemosensor 1, based on a thiourea-activated phthalimide, is available by four reaction steps from 4-nitrophthalimide. 1 detects fluoride, chloride, acetate, and dihydrogen phosphate anions by changes in UV-vis absorption. Fluoride in excess induces deprotonation whereas the other anions show only complex formation in the ground state. (1)H-NMR studies confirm the formation of these H-bonded complexes and the fluoride-induced receptor deprotonation in the recognition process. Moderate chiral recognition was observed for sodium D/L-lactate with K(ass)(D)/K(ass)(L) = 1.93.
The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity.
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