Molecular two-photon absorption (TPA) has attracted a lot of interest over recent years due to the many applications it offers both in biological imaging and in material science, constantly needing new optimized molecules with large TPA cross-sections. Various structures and functional groups have been studied; however, the use of electron-withdrawing boron groups has not been fully examined yet. As such compounds are known to lead to interesting photoluminescence and nonlinear optical (NLO) properties, we have investigated the TPA properties of a novel series of A-π-A quadrupoles, based on dimesitylborons as acceptor end-groups. Our experimental study reveals that intramolecular charge transfer is a crucial point in these TPA fluorophores, and can be modulated via changing the planarity of the molecule. We have obtained such planar molecules using vinylene spacers, which can release the steric hindrance close to the dimesitylboron end-group. The series of NLO-phores described here is promising for optical power limiting, with excellent TPA/transparency trade-off, and the work has highlighted that perfluorophenylene could be a key component for the future of TPA.
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