One-Photon and Two-Photon Absorption Properties of Multi-Branched Squaraine Dyes Comprised of Triphenylamine Cores and Ethynylene Linkers

We developed multi-branched & pi;-conjugated systems using squaraine dyes with triphenylamine cores connected by ethynylene linkers. We investigated the influence of interbranch coupling between squaraine branches on their one-photon (OPA) and two-photon absorption (TPA) properties. These dyes with triphenylamine components showed a red-shifted one-photon absorption (OPA) compared to the precursor squaraine dyes. Among branched dyes, the lack of apparent splitting or shift in the absorption maxima, even as the absorption intensity increased with the number of chromophores, implies the presence of limited exciton coupling between the squaraine branches. The present squaraine dyes with triphenylamine cores exhibited a moderate TPA compared to the precursor squaraine without the triphenylamine core, due to the extended & pi;-conjugation. Notably, both the 3-branched and 2-branched dyes demonstrated additional enhancement in the TPA response, surpassing that of the monochromophoric counterpart. This resulted in achieving a substantial TPA cross section of up to 3905 GM at 830 nm. The squaraine chromophores, which have single, two-branched, and three-branched structures with ethynyl-triphenylamine central units, exhibit efficient two-photon absorption (TPA) with a cross section that corresponds to the number of branches present, indicating an additive effect. Among these chromophores, the three-branched dye displays the highest TPA cross section, reaching a maximum value of 4.0x103 GM.image

Automated summary

In this study, we developed multi-branched and π-conjugated systems using squaraine dyes with triphenylamine cores connected by ethynylene linkers. We found that the interbranch coupling between squaraine branches significantly influenced their one-photon and two-photon absorption properties. Introducing triphenylamine cores in the squaraine dyes resulted in a red-shifted one-photon absorption and the increased absorption intensity with the number of chromophores, without apparent splitting or shift in absorption maxima. Moreover, the extended π-conjugation in these squaraine dyes with triphenylamine cores led to a significant enhancement in two-photon absorption. Notably, the 3-branched and 2-branched dyes demonstrated additional enhancement in two-photon absorption response, surpassing that of the monochromophoric counterpart.