Synthesis, Photophysical Investigation, and Nitroaromatic Sensing Properties of Novel Fused Pyrrolo[1,2-f]azolo[1,5-a]pteridines.

A novel series of pyrrolo[1,2-f]azolo[1,5-a]pteridines has been synthesized via an efficient two-step annulation strategy. The photophysical properties of the resulting polyheteroaromatic fluorophores were systematically investigated in solution, solid state, and polymer films. In THF, the compounds exhibit intense emission in the visible region with high quantum yields (Ф up to 79.9%) and lifetimes of 10-13 ns. Solvatochromic studies reveal small positive solvatochromic shifts with increasing solvent polarity, and Lippert-Mataga analysis indicates a predominantly locally-excited (LE) state. While aggregation leads to quenching in the solid state, embedding in PVA films restores emission efficiency. The electron-rich scaffold shows pronounced fluorescence quenching in the presence of nitroaromatic analytes, including picric acid (PA) and 2,4-dinitrotoluene (DNT), with Stern-Volmer constants up to 9.2 × 103 M-1 and detection limits down to 1.56 ppm. The quenching behavior is predominantly attributed to photoinduced electron transfer, demonstrating the potential of this new fluorophore class for nitroaromatic sensing applications. The combination of high fluorescence efficiency and sensitivity toward nitroaromatic compounds demonstrates that pyrrolo[1,2-f]azolo[1,5-a]pteridines systems represent a promising platform for the development of functional photonic materials and fluorescent sensors.