Density functional theoretical studies on photoswitching and charge migration dynamics of thio and selenoureidopeptides

Abstract

Density functional theoretical calculations have been performed to investigate the changes in electronic structure at ground and excited states of ureidopeptides on substitution with higher chalcogens like sulphur and selenium for oxygen. This replacement results in a reduced preference towards the intramolecular hydrogen bonding interaction, thus linear conformers are found to be stable at both states.Nevertheless, conformational switching observed during this process is mainly due to n to π* transition that leads to the dihedral angle ω change from trans to cis with a rotational barrier of 10 to 17 kcal mol -1 . The computed barrier is lesser than that reported for oxopeptides (20 kcal mol -1 ). And, the hole migration dynamics after immediate ionization illustrates that the hole originated at ureido end evolves in time (2−4 fs) while the hole generated at the carboxylate end will not evolve as reported for ureidopeptides. The usage of these candidates as photoswitches has also been explored.