Controllable Photophysical and Nonlinear Properties in Conformation Isomerization of Macrocyclic [32]Octaphyrin(1.0.1.0.1.0.1.0) Involving Huckel and Mobius Topologies

The conversions of photophysical and nonlinear optical (NLO) properties in [32]octaphyrins(1.0.1.0.1.0.1.0) following macrocyclic isomerization between Huckel and Mobius topologies have been studied in detail by means of quantum chemistry calculations. Compared to their quasi-planar analogues, the twisted Mobius and the figure-eight Huckel conformers exhibit red- and blue-shifted absorptions, respectively. The fluorescence emissions of Huckel topological molecules are likely to be from the second excited state, while the Mobius ones should emit photons from the first excited state by following Kasha's rule. The average polarizabilities of octaphyrins reveal certain regularity with regard to their topologies, but is not particularly large; with the pi-conjugation enhanced, the polarizability value increased moderately. The static first- and second-order hyperpolarizabilities of Mobius conformations are almost all much higher than those of Huckel conformers, and the figure-eight Huckel structures exhibit relatively high values than the quasi-planar Huckel ones. Regarding the frequency dispersions under the incident light, the strong optical resonance effects were found on the first- and second-order hyperpolarizability of molecules, which contrast with the fact that it has modest influences on the average polarizability. The primary cause of the performance differences in optical properties of the octaphyrins has also been probed from different perspectives by various methods of electronic wavefunction analysis. Generally, we confirm that the topological transformation of expanded porphyrins can be used as a special switch to trigger various optical properties.