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

Abstract We developed multi‐branched π‐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 π‐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.