| Summary: | Nonlinear optical (NLO) pigments are compounds insoluble in solvents that exhibit phenomena related to nonlinear optical susceptibilities (χ<sup>(n)</sup> where n = 2,3,...), e.g., two-photon absorption (2PA) which is related to the imaginary part of χ<sup>(3)</sup>. Determination of spectrally-resolved 2PA properties for NLO pigments of macromolecular nature, such as coordination polymers or crosslinked polymers, has long been a challenging issue due to their particulate form, precluding characterizations with standard techniques such as Z-scan. In this contribution, we investigate thus far unknown spectrally-resolved 2PA properties of a new subclass of NLO pigments—crosslinked conjugated polymers. The studied compounds are built up from electron-donating (triphenylamine) and electron-withdrawing (2,2’-bipyridine) structural fragments joined by vinylene (<b>Pol1</b>) or vinyl(4-ethynylphenyl) (<b>Pol2</b>) aromatic bridges. 2PA properties of these polymers have been characterized in broad spectral range by specially modified two-photon excited fluorescence (TPEF) techniques: solid state TPEF (SSTPEF) and internal standard TPEF (ISTPEF). The impact of self-aggregation of aromatic backbones on the 2PA properties of the polymers has been evaluated through extended comparisons of NLO parameters, i.e., 2PA cross sections (σ<sub>2</sub>) and molar-mass normalized 2PA merit factors (σ<sub>2</sub>/M) with those of small-molecular model compounds: <b>Mod1</b> and <b>Mod2</b>. By doing this, we found that the 2PA response of <b>Pol1</b> and <b>Pol2</b> is improved 2–3 times versus respective model compounds in the solid state form. Further comparisons with 2PA results collected for diluted solutions of <b>Mod1</b> and <b>Mod2</b> supports the notion that self-aggregated structure contributes to the observed enhancement of 2PA response. On the other hand, it is clear that <b>Pol1</b> and <b>Pol2</b> suffer from aggregation-caused quenching phenomenon, well reflected in time-resolved fluorescence properties as well as in relatively low values of quantum yield of fluorescence. Accordingly, despite improved intrinsic 2PA response, the effective intensity of two-photon excited emission for <b>Pol1</b> and <b>Pol2</b> is slightly lower relative to <b>Mod1</b> and <b>Mod2</b>. Finally, we explore temperature-resolved luminescence properties under one- (377 nm), two- (820 nm), and three-photon excitation (1020 nm) conditions of postsynthetically Eu<sup>3+</sup>-functionalized material, <b>Pol1-Eu</b>, and discuss its suitability for temperature sensing applications.
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