Synthesis and Photophysical Evaluation of Dialkynyl-N-(het)arylpyrroles: Promising Key Compounds in Fluorescence Chemistry

In this work, we present a series of chromophores based on dialkynyl-N-(het)arylpyrrole, featuring diverse combinations of donor-acceptor moieties. The study explores the potential of fluorophores derived from (alkynyl)arylpyrroles, investigating the impact of the central core's nature with phenyl and pyridyl groups, along with various arylethynyl groups. Additionally, we assess these derivatives in the selective synthesis of non-symmetrical ullazine derivatives with broad photophysical potential through photocatalysis. The precursors exhibit absorption maxima in the UVB region (similar to 300 nm), while the model mono-ullazine displays absorption maxima in the UVA region (similar to 320 nm). Emission maxima for the precursors are observed between the UVA and violet regions, with the emission wavelength tailored by the substituents. In contrast, the mono-ullazine fluoresces in the blue region. Remarkably, selected compounds exhibit an intricate photophysical behavior where a dual fluorescence emission with a large Stokes shift was present, which could not be clearly related to an intramolecular charge transfer (ICT) mechanism. Theoretical calculations support the experimental findings.