Density functional theory study on thermal isomerization of β-carotene

The density functional theory method B3LYP is employed to study the thermal isomerization of β-carotene. The results present the following sequence of stability of neutral isomers: all-trans > 9-cis > 13-cis > 9,13-di-cis = 9,13′-di-cis > 15-cis > 9,15-di-cis > 13,15-di-cis > 7-cis > 11-cis. PCM calculations show that all isomers are influenced by the stabilizing effect of melting. The mechanism of thermal isomerization suggests that the isomerization of β-carotene occurs primarily via the radical cation while triplet-excited β-carotene is also a possible intermediate of isomerization, especially under mild conditions.