Background-free fluorescence decay time sensing and imaging of pH with highly photostable diazaoxotriangulenium dyes

摘要： Novel fluorescent diazaoxatriangulenium (DAOTA) pH indicators for lifetime-based self-referenced pH sensing are reported. The DAOTA dyes were decorated with phenolic receptor groups inducing fluorescence quenching via photoinduced electron transfer mechanism. Electron-withdrawing chlorine substituents ensure response in the most relevant pH range (apparent pK’a values ~5 and 7.5 for the p,p-dichlorophenol- and the p-chlorophenol-substituted dyes, respectively). The dyes feature long fluorescence lifetime (17-20 ns), high quantum yield (~60%) and high photostability. Planar optodes are prepared upon immobilization of the dyes into polyurethane hydrogel D4. Apart from the response in the fluorescence intensity, the optodes show pH-dependent lifetime behaviour which makes them suitable for studying 2D pH distribution with help of fluorescence lifetime imaging technique. The lifetime response is particularly pronounced for the sensors with high dye concentration (0.5-1% wt. in respect to the polymer) and is attributed to efficient homo-FRET mechanism.