Solvation dynamics of coumarin 153 in molten salts

Static and time-resolved fluorescence techniques are employed to measure the solvation statics and dynamics of electronically excited coumarin 153 in several molten tetraalkylammonium salts. The solvation of coumarin 153 occurs on two time scales which are both dependent on the cation size. The larger the cation size, the longer the relaxation time. For coumarin 153 in molten tetrabutylammonium hydrogen sulfate, the Stokes shift relaxation times are ∼40 and 220 ps for the short and long component respectively. For coumarin 153 in molten tetradodecylammonium perchlorate, the relaxation times are 200 and 2000 ps. The steady-state emission band position is strongly dependent on the molten salt cation size. The band maximum position for coumarin 153 in molten tetrapropylammonium hydrogen sulfate is at 18 250 cm^-1 (548 nm), while for tetradodecylammonium perchlorate the band maximum is at 20 120 cm^-1 (497 nm).