Influence of rotational isomerism on two-photon absorption properties of FTC chromophores

The influence of rotational isomerism on the two-photon absorption (TPA) of FTC chromophores has been investigated by using the quadratic response theory with the B3LYP functional. Eight rotamers induced by three rotatable single bonds in the molecule are fully optimized, and it is found that their conformational energies are nearly degenerate. Our calculations demonstrate that the rotational isomerism has important effects on the TPA cross sections. For a certain rotamer, the maximum TPA cross section is enhanced significantly. Also, in the longer wavelength region, the rotational isomerism could lead to a large shift of the TPA position.