Linear allenic linkage for nonlinear optics: A computational study of the role of mutually orthogonal π-orbitals in controlling the charge transfer, hyperpolarizability and absorption properties in some donor-acceptor substituted allenes

First hyperpolarizability (β) of some donor-acceptor substituted allenes where, unlike in the earlier studies, the donor and acceptors are mutually orthogonal to each other are carried out using couple perturbed Hartree-Fock (CPHF) method at HF/6-31G level of theory. All the molecules show reasonably good β values. Configuration interaction singles (CIS) analysis shows that most of the molecules absorb in the UV-region and thus are transparent in the region of interest. On the other hand, zwitterionic allenes show unusually smaller β values. Analysis shows that, structural deformation in zwitterionic allenes leads to a through space (TS) charge transfer and ultimately reducing the β. But in zwitterionic allenes with resonance stabilized donors, enhancement in β can be achieved. It is suggested that with the absorption in the UV region, reasonably good values of β and the chirality due to asymmetric substitution, these molecules could be potential candidates for device applications.