Collisional Deactivation of Vibrationally Highly Excited Azulene in Supercritical Fluids

The collisional deactivation of vibrationally highly excited azulene was studied from gas into compressed liquid phase by pump-and-probe picosecond laser spectroscopy. Collisional deactivation rates were compared with solvatochromic shifts Δν of the azulene S3←S0 absorption band under identical conditions. Employing supercritical fluids at pressures between 0.03 and 4000 bars and temperatures between 298 and 640 K, measurements covering the complete gas–liquid transition were performed. For the energy transfer experiments, azulene with an energy of ∼20000 cm−1 was generated by laser excitation into the S1- and internal conversion to the S0*-ground state. The subsequent loss of vibrational energy was monitored by following the transient absorption at the red wing of the S3←S0 absorption band near 290 nm. Transient signals were converted into energy-time profiles using hot band absorption coefficients from shock wave experiments for calibration and accounting for solvent shifts of the spectra. Under all con...