One- and two-photon absorption properties of quadrupolar A–π–D–π–A dyes with donors of varying strengths

In this work, the one- and two-photon absorption properties of two quadrupolar A–π–D–π–A dyes, featuring carbazole and triphenylamine as donors of varying strengths, are calculated using density functional theory. The characteristics of two-photon excitation are analysed by using the three-state model closest to the real physical process. By taking the intermediate state as a bridge, the charge transfer characteristics in the two-photon excitation process are studied in detail by using various visualisation methods. Comparing the intramolecular charge transfer (ICT) characteristics shows that increasing the ability of the push-pull electrons of the central substituents, thus increasing the intramolecular charge transfer, is a more efficient method to enhance the molecular σ_tp. Our study promotes a deeper understanding of the design of A–π–D–π–A molecules with large cross-sections in two-photon absorption.