Ultrafast polyene dynamics in solution: The conformational relaxation and thermalization of highly excited cis-1,3,5-hexatriene as a function of initial conformation and solvent
Na. Anderson et al., Ultrafast polyene dynamics in solution: The conformational relaxation and thermalization of highly excited cis-1,3,5-hexatriene as a function of initial conformation and solvent, J PHYS CH A, 102(52), 1998, pp. 10588-10598
Femtosecond transient absorption spectroscopy has been used to investigate
the ground and excited-state dynamics of cis-1,3,5-hexatriene (Z-HT) and 1,
3-cyclohexadiene following excitation to the strongly allowed 1(1)B state i
n cyclohexane and n-hexadecane solvents. The internal conversion from the e
xcited state manifold to produce vibrationally excited ground electronic st
ate Z-HT occurs with rates of ca. 2-4 ps(-1). The relaxation of highly exci
ted Z-HT is used to probe the solvent-solute interaction and the influence
of solvent on the competition between thermalization and single-bond isomer
ization dynamics. The data are also used to compare and contrast the hexatr
iene relaxation as a function of solute initial conditions (cZc-NT vs tZt-H
T). A formalism for transforming the observed spectral data into time-depen
dent photoproduct yields is developed. These data are then compared with ti
me-dependent quantum yields obtained from a transition state, rate equation
approach to modeling the anticipated population dynamics. The detailed ana
lysis of the results presented here are compared with the analysis of Lochb
runner et al. [Lochbrunner, S.; Fuss, W.; Schmid, W. E.; Kompa, K.-L. J. Ph
ys. Chem. A 1998, 102, 9334. In press.] for the conformational relaxation o
f highly excited ZHT in ethanol. Although the conformational evolution obse
rved in hexadecane and cyclohexane are similar, the decays of cZc-HT and cZ
t-HT appear to be substantially faster in ethanol. These results are discus
sed in the context of Kramers theory for condensed phase reaction dynamics.