Catalán J, de Paz JLG. On the photophysics of all-transpolyenes: Hexatriene versus octatetraene.
J Chem Phys 2006;
124:034306. [PMID:
16438582 DOI:
10.1063/1.2158992]
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Abstract
The disparate photophysical behavior of trans-1,3,5-hexatriene (nonfluorescent) and trans-1,3,5,7-octatetraene (with two fluorescence emissions) in the gas phase is explained in terms of the tendency of their 1B(u) excited states to rotate about their terminal carbon-carbon single bonds in order to adopt a quasiplanar molecular form of lower energy than the 1B(u) state in the parent all-trans structure. The origin of their disparate photophysical behavior is that such a transformation is subject to a small energy barrier in octatetraene; the barrier produces two minima (two fluorescence emissions) in the corresponding potential-energy curve. Instead of an energy barrier, hexatriene gives a 1,3-diene species which falls to the ground state so rapidly that no emission is produced.
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