Electronically excited states in π/π stacking compounds*

In particular, π/π stacking compounds have become of interest in new materials for photocatalysis, solar energy and phosphorescent organic light-emitting diodes. We investigate theoretically the photo-induced charge transfer in supramolecular chemistry such as a bowl-shaped polycyclic hydrocarbon and helical ortho-position linked phenylenes (OPs). The electronically excited states and absorption spectra of these materials were first studied by using TD- DFT calculations with various functionals. The functional that best reproduced the experimental results was found to be wB97XD, and the assignment of the experimentally observed UV-Vis absorption spectrum was successfully performed in comparison with the theoretically obtained one. We especially performed spectral assignment of the carbazole (Cz) -modified OP complexes. The results showed that the absorption spectrum of the complexes consisted of (i) an n–π^* charge-transfer type transition from Cz to OPs units of longer wavelength at around 290 nm and the π–π^* transition of a shorter wavelength at around 230 nm, and (ii) the components of three isomers which coexist with three kinds of substitution of Cz to OPs, such as ortho, meta and para linkage of Cz, to interconnect the aromatic units of the Ops.