Double-helix P_:NLi_n chains: Novel potential nonlinear optical materials

The structures, circular dichroism (CD) spectra and nonlinear optical (NLO) responses of a series of inorganic double-helix chains, P_nLi_n (n = 6-12), have been investigated using the quantum chemistry method. P-P and P-Li interactions play a major role in stabilizing double-helix chains. The distinctive CD spectra of the double-helix frameworks (namely, a sharp negative CD band at short-wavelength region and a positive CD band at long-wavelength region) become obvious with increasing number of PLi units. The NLO response augments with the length of the double-helix chains, and the contribution of the axial component along the chain direction gradually becomes crucial simultaneously. Synergistic effects, a decrease of crucial electronic transition energies and charge transfer excitation give rise to enhanced NLO responses. In particular, the electronic transitions from the highest occupied molecular orbital to the lowest unoccupied molecular orbital make significant contributions not only to the positive CD bands in the long-wavelength region, but also to the NLO responses of the double-helix P_nLi_n (n = 6-12) chains.