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Optothermal detection has been used to observe non-radiative relaxation channels in aniline, {p}-bromoaniline and {trans}-stilbene. A comparison of aniline and {p}-bromoaniline exemplifies the power of this technique. {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 detection spectrum of {p}-bromoaniline was observed with the origin at $32625cm-1$. For {trans}-stilbene the differences between the laser excitation spectrum and the optothermal detection spectrum of the $S1$ state clearly show the onset of isomerization at $1100-1200cm-1$ above the origin. Relative quantum yields of fluorescence and Franck-Condon factors 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 the predicted relative quantum yields do not agree with our experimental results. Our results show that the Frank-Condon factors are more important in the loss of fluorescence intensity than previously reported.