The applicability of binary collision theories to complex molecules in simple liquids

Abstract

The relaxation dynamics of vibrationally excited ground-state azulene molecules have been examined by picosecond transient absorption spectroscopy in a variety of different solvents including hexane, chloromethanes, methanol, CClF3, Xe, and Kr. A high pressure optical cell was used to liquify gases for use as solvents and to change their density and temperature independently over the entire liquid density range. Experimental results indicate that the vibrational cooling rate is strongly solvent dependent, with cooling rates of approximately 20 ps in molecular solvents and approximately 150 ps in atomic solvents. Comparison of the rates in Xe and Kr at constant number density demonstrates the strong effect of solvent mass on energy transfer. The effect of solvent temperature on vibrational cooling is minimal, as is the effect of solvent density. The latter result is quite surprising in light of earlier experiments on simpler molecular systems, such as I2 in Xe, and predictions of isolated binary collision theories. An explanation is offered from large scale molecular dynamics simulations of the system. In effect, azulene forms an ‘‘ordered Xe cluster’’ with xenon atoms; the xenon number density normal to the azulene molecular plane is independent of solvent density.

The Role of Hydrogen‐Bonding Interactions in the Ultrafast Relaxation Dynamics of the Excited States of 3‐ and 4‐Aminofluoren‐9‐ones

“…The second component with a lifetime of 11 ps agrees well with the lifetime of the longitudinal relaxation time of methanol ( % 9.2 ps) and hence can be assigned to the solvent reorganization process. [30,48] This assignment can only be confirmed by the results of analysis of the temporal profiles recorded at other wavelengths as well as in other alcoholic solvents (see below).…”

“…The possible reason behind this may be the choice of the probe molecules, which do not display much difference in fluorescence behavior in protic and aprotic solvents because of weak hydrogen-bonding interaction between the solute and solvent. [29][30][31][32][33] Recently, Morimoto et al studied the fluorescence quenching of a series of aromatic carbonyl compounds by alcoholic solvents. [23] This work revealed that the S 1 states of 3AF and 4AF are more efficiently quenched by alcohols than those of two coumarin dyes, namely, coumarin 153 (C153) and coumarin 151 (C151).…”

“…[5,[20][21][22][23][24][25][26] The nature of coupling between the solute and solvent molecules also governs the rate and mechanism of the transfer of excess vibrational energy of the excited state of the solute to the solvent bath. [27][28][29][30] Secondly, the hydrogenbonding interaction between the solute and solvent in the first solvation cell also plays an important role in the dynamics of solvation as well as the relaxation processes undergone by the excited states. [31][32][33][34][35][36][37] Additionally, this interaction is always associated with the reorganization of the hydrogen-bond network structure of the solvent.…”

Ultrafast Dynamics of the Excited States of Hydrogen‐Bonded Complexes and Solvation

“…Firstly, it is wellestablished that both intra-as well as intermolecular hydrogen bonds act as accepting modes for the nonradiative electronic energy of the excited state, providing an efficient radiationless deactivation pathway, and its lifetime is strongly quenched [16][17][18][19][20][21][22][23]. The nature of coupling between the solute and the solvent molecules also governs the rate and mechanism of the transfer of excess vibrational energy of the excited state of the solute to the solvent bath [24][25][26][27]. Secondly, the hydrogen-bonding interaction between the solute and the solvent molecules in the first solvation cell also plays an important role in the dynamics of solvation, as well as the relaxation processes undergone by the excited states [10,[28][29][30][31][32][33].…”

Experimental and theoretical study of inhomogeneous electron transfer in betaine: comparisons of measured and predicted spectral dynamics

“…J Pe(X,t) dX S(t) P eXt_)____ (6) f Pe(X,0) dX 16 Figure 15 shows S(t) for betaine in acetone assuming broadband excitation and selective excitation at 800 nm, 700 nm, and 640 nm. In all four cases, there is an induction period at early time during which the electron-transfer rate is very small.…”