A new frequency-domain fluorometer for the rapid determination of picosecond rotational-correlation times

Abstract

A new instrument is described which uses the harmonic content of a mode-locked argon-ion laser for the determination of picosecond rotational-correlation times. The new instrument is very rapid, and can detect in about 8 ms all frequencies between dc and 750 MHz. The signal-averaging capabilities of the instrument also make it applicable to weakly fluorescent species. To test the new instrument, the time-dependent fluorescence polarization of rhodamine 6G was studied as a function of solvent viscosity; a second chemical system investigated was fluorescein in 1,3-propanediol. Both these systems were chosen because they have been shown to exhibit a single rotational-correlation time. Results are in good agreement with those previously reported.