Detection of ultrafast solvent dynamics employing a streak camera

Abstract

The ultrafast solvent dynamics of glycerol and ethylene glycol (EG) in response to a sudden charge jump in two different solute probes, coumarin 153 (C153) and trans-2-[4-(dimethylamino)styryl] benzothiazole (DMASBT), were measured by employing streak camera-based detection system (temporal resolution ~2ps). Subsequently, the detection of time-dependent solvation of the excited solute was measured by appropriately combining the streak camera data with those from the time-correlated single photon counting (TCSPC) measurements (resolution ~90 ps). Interestingly, combined data for C153 provided dynamic Stokes shift magnitudes approximately double the magnitudes accessed via the streak camera alone for these two solute probes in glycerol and EG. The initial phase of solvation in EG was found to be too fast to be measured by the present streak camera-based detection set-up and missed nearly half of the total response. The relatively shorter average excited state fluorescence lifetime of DMASBT (\(\langle {\tau }_{fl}\rangle <0.5 \mathrm{ns}\)) prohibited the detection of the \(\ge\) 0.5 ns solvation component reported by C153 in glycerol, highlighting the importance of \(\langle {\tau }_{fl}\rangle\) for complete measurements of polar solvation response via dynamic Stokes shift measurements. Inappropriate choice of fluorescent probe solute with shorter \(\langle {\tau }_{fl}\rangle\) may therefore give rise to an unexpected solute dependence of polar solvation dynamics even when detection of the rapid initial decay is ensured through ultrafast measurements.

Graphical abstract

Graphical Abstract presenting schematically the measurements of the solvation response function by processing the relevant streak camera images and the time-correlated photon counting (TCSPC) data and appropriately combining them together.