Luminescent Probe for Highly Energetic Collisions in Mixtures of Complex Molecules with Acceptors of Vibrational and Triplet Energy

Abstract

Pressure dependences of intensities and decay rates of time-resolved luminescence of acetophenone, benzophenone, anthraquinone were used to obtain the efficiencies of vibrational and triplet-triplet energy transfer. It was shown that vibrational relaxation of the chosen molecules can be interpreted in terms of two consecutive processes: rapid collisional relaxation of molecules from initially prepared states to a vibrational distribution at Tvib by vibration-vibration process and relaxation of this vibrational distribution to the thermal one (vibration-translation process). At relatively small internal eneigy < 10000 cm -", the collisional efficiencies of the vibration-vibration process in mixtures with polyatomic bath gases had values typical of processes with a supercollision contribution. Molecules relaxed from the upper vibrational level to the vibrational distribution after several collisions (2-3). The average energies transferred per collision are well correlated with predictions of the simple ergodic theory of collisional energy transfer. The majority of the collisions took part only in vibration-translation energy transfer of relatively small energies. The efficiencies of triplet-triplet energy transfer were analyzed for acetophenone, benzophenone and anthraquinone as donors and biacetyl-acceptor in a gas phase when energy of about 20000 cm' was transferred. It permitted us to elucidate the common features of highly energetic collisions. It was shown that the efficiencies are much lower than the gas kinetic ones and depended on the vibrational energy and temperature. It was discussed how to enhance triplet-triplet efficiencies due to vibrational excitation of a donor molecule.

Intermolecular Processes in Excited Electronic States in the Gas Phase (Review)

“…The applicability of the statistical models assuming the establishment of vibrational equilibrium in the collision time becomes better with increasing time resolution of the experiment as well as with account of the temperature changes in the mean vibrational energy of interacting molecules E vib [5,7,10,11]. For the molecules being investigated, the densities of vibrational levels N(E i ) were calculated preliminarily by the complete set n of vibrational frequencies in a wide range of vibrational energies E i , and then the values of…”

“…To estimate the rate constants and efficiencies of the T-T electron energy transfer, the widely used method for investigating the T-T transfer by the quenching of the delayed luminescence (phosphorescence and DF) of the donor by the acceptor and by the sensitization of delayed fluorescences of acceptors was employed [11,[33][34][35][36][37][38]. The temperature dependences of the kinetic characteristics of the T-T transfer were investigated for seven DA pairs in the 363-513 K temperature range.…”