Quantum chemical study of electronic and structural properties of retinal and some aromatic analogs.

The electronic and structural properties of retinal and four analogs were studied using semiempirical, ab initio Hartree-Fock, and density functional theory methods with the aim to evaluate the effects caused by some structural modifications in the ring bound to the polyenic chain and compared with the all-E-trans-retinal molecule. Therefore, some properties such as bond lengths, bond angles, atomic charges derived from electrostatic potential charges from electrostatic potential using grid based method as well as frontier orbitals of the polyenic chain were analyzed. Furthermore, the transition energies of the molecules were also calculated using the Zerner's intermediate neglect of differential overlap-spectroscopic, time-dependent Hartree-Fock, and time-dependent density functional theory methods. The results indicate that in spite of the structural modifications of retinal derivatives in comparison with all-E-trans-retinal, their properties seem similar. Thus, these molecules may behave similarly to all-E-trans-retinal and possibly be attempted in the search of novel molecular devices.