2,4-Bis(4-aryl-1,2,3-triazol-1-yl)pyrrolo[2,3-d]pyrimidines: synthesis and tuning of optical properties by polar substituents

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2,4-Bis(4-aryl-1,2,3-triazol-1-yl)pyrrolo[2,3-d]pyrimidines as D–p–A–p–D chromophores were successfully prepared by CuAAC reaction of 2,4-diazido-7-methylpyrrolo[2,3-d]pyrimidine with ethynylarenes in dichloromethane in the presence CuI/DIPEA/AcOH as a catalyst system. The incorporation of small polar substituents enabled tuning of the energy of frontier orbitals and thus the FMOs energy gap by up to 0.9 eV, while the incorporation of bulky steric substituents resulted in narrowing of the energy gap by up to 0.4 eV. Owing to electron-accepting properties of pyrrolo[2,3-d]- pyrimidine core extending to triazole moieties the compounds with electron-donating groups showed expressed intramolecular charge transfer character (ICT) of the excited states which was proved by solvatochromic dynamics and supported by DFT calculations. The optimization of ICT reduced radiative and non-radiative deactivation pathways resulted in enhancement of fluorescence quantum yield up to 73%.

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