Optothermal detection of nonradiative relaxation channels in electronically excited molecules

Miller, C. Cameron; Hewett, Kevin B.; Shen, Meihua; Philips, Laura A.
January 1995
Journal of Chemical Physics;1/1/1995, Vol. 102 Issue 1, p145
Academic Journal
Optothermal detection has been used to observe nonradiative relaxation channels in aniline, p-bromoaniline, and trans-stilbene. p-Bromoaniline has no detectable fluorescence due to a heavy atom effect which increases the rate of intersystem crossing to the triplet state. An optothermal spectrum of p-bromoaniline was observed with the origin at 32 625 cm-1. For trans-stilbene, the differences between the laser excitation spectrum and the optothermal spectrum of the S1 state clearly show the onset of isomerization at ∼1250 cm-1 above the origin. Absolute quantum yields of fluorescence, Franck–Condon factors, nonradiative rates, and radiative rates have been obtained for a series of vibronic transitions. For low energy vibrational states, there is good agreement between the current study and previous work. For vibrational energies above the barrier of isomerization, predicted quantum yields do not agree with our experimental results. © 1995 American Institute of Physics.


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