Photochemical hole burning for 1,3,5,7-octatetraene in <i>n</i>-hexane

Abstract

It is now well established that the unsubstituted linear polyene 1,3,5,7-octatetraene efficiently undergoes cis–trans photoisomerization even when substituted in an n-alkane matrix cooled to liquid-helium temperatures. The fact that this photochemical reaction takes place under these conditions opens the possibility of using the techniques of photochemical hole burning to uncover details of the microscopic mechanism of this isomerization. In this paper we report the demonstration of photochemical hole burning for all-trans-octatetraene in n-hexane, show that the hole width for the zero-phonon component of the 0–0 band in the limit of zero temperature and zero hole depth is within experimental error equal to the value predicted from the measured fluorescence lifetime, analyze the dependence of hole width on temperature, and show that the relative quantum yield for hole burning increases by approximately a factor of 35 as vibrational energy in the excited state is increased beyond a threshold of approximately 950 cm−1. This threshold agrees well with the previously determined barrier to trans, cis isomerization.