Differently substituted pyrrole-azo‑benzene molecular photoswitches were prepared in a straightforward synthetic way. Their fundamental properties were investigated by XRD analysis, differential scanning calorimetry, thermogravimetric analysis, cyclic voltammetry, UV‑Vis absorption spectroscopy, Hyper-Rayleigh Scattering, and NMR spectroscopy; the experimental results were further corroborated by DFT calculations. Thermal robustness, the HOMO/LUMO levels, and the absorption properties were altered mostly by substituting the N‑methylpyrrole moiety and further fine-tuned by modifying the benzene substituents. The pyrrole substituent also proved crucial for the second-order non-linear optical (NLO) response as well as the photoswitching performance. Both fast and slow molecular switches can be designed with the half‑life of the (Z)‑isomer ranging from 48 seconds to 23.28 hours and the E/Z molar ratio up to 12/88. This comprehensive study allowed elucidation of the fundamental structure-property relationships and subsequently addresses the key aspects of the property tuning via substitution in molecular azo-photoswitches.
Keywords: azo-compounds * Hyper Rayleigh scattering * non linear optics * photoswitch * pyrrole.
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