On the photophysics of all-trans polyenes: hexatriene versus octatetraene.
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.
Catalán
J
J
Departamento de Química Física Aplicada, Universidad Autónoma, C-II-203, Cantoblanco, 28049 Madrid, Spain. javier.catalan@uam.es
de Paz
J L G
JL