Effect of donor–acceptor orientation on solvent-dependent three-photon activity in through-space charge-transfer systems – case study of [2,2]-paracyclophane derivatives

Abstract

We study the effect of donor–acceptor orientation on solvent-dependent three-photon transition probabilities (δ^3PA) of representative through-space charge-transfer (TSCT) systems, namely, doubly positively charged [2,2]-paracyclophane derivatives. Our cubic response calculations reveal that the value of δ^3PA may be as high as 10⁶ a.u., which can further be increased by a specific orientation of the donor–acceptor moieties. To explain the origin of the solvent cum orientation dependency of δ^3PA, we have calculated different three-photon tensor components using a two-state model, noting that only a few tensor elements contribute significantly to the overall δ^3PA value. We show that this dependence is due to the large dipole moment difference between the ground and excited states of the systems. The dominance of a few tensor elements indicates a synergistic involvement of π-conjugation and TSCT in the large δ^3PA of these systems.