Abstract:

The geometries of a series of binaphthyl bridged chiral bis-porphyrins were optimized using B3LYP method at 6-31G(d,p) basis set level. The electronic spectra of these porphyrins were then calculated using the semi-empirical ZINDO/S method. Results showed that strong exciton coupling interactions between the two porphyrin chromophores existed in these bis-porphyrins. Davydov splitting of the B bands were related to both the distances and the relative orientations of the two porphyrin rings. First hyperpolarizabilities of these porphyrins were calculated using the ZINDO/SOS method. The second-order nonlinear optical properties of the binaphthyl bridged chiral bis-porphyrins were greatly improved by introducing push/pull substituents onto the porphyrin chromophore. The first hyperpolarizabilities of binaphthyl bridged chiral bis-porphyrins depend on the spatial arrangement of the substituents. The increase in first hyperpolarizabilities of bis-porphyrins is not only related to increasing the dipole moment different between excited and ground state, but also to the relative orientations between the ground state dipole moment vectors and the exciton coupling transition moment vectors.

Key words: Electronic spectrum, Chiral bis-porphyrins, Second-order nonlinear optical property, Sum-over-states