Isoindole-Based Multicomponent Synthesis of Pyrimido[6,1,2- cd ]pyrrolizine Fluorophores with Unsymmetrical Urea Handles: Photophysical, Theoretical, and Antifungal Imaging Studies

Abstract A diversity-oriented, one-pot synthetic strategy was successfully employed to generate a library of pyrimido[6,1,2-cd]pyrrolizine (PP)-based fluorophores incorporating unsymmetrical urea functionality, which function as versatile fluorescent probes and pharmacophores. These PP derivatives, efficiently constructed via multicomponent reaction pathways from readily accessible precursors, exhibit an intense orange-red fluorescence in solution. Incorporation of appendage diversity in the side chain induces significant solid-state bathochromic shifts, with emission maxima extending close to the near-infrared region (NIR). Single-crystal X-ray diffraction analysis elucidated the intermolecular interactions and the packing motifs. Complementary theoretical investigations (DFT and TD-DFT) and molecular electrostatic potential (MEP) analyses provided mechanistic insight into their photophysical properties. Furthermore, cellular imaging studies in Candida albicans demonstrated efficient uptake and distinct intracellular localization, highlighting the potential of PP fluorophores as versatile probes for advanced biological applications. Collectively, the PP framework represents a promising fluorescent pharmacophore, exhibiting measurable antifungal activity while enabling precise fluorescent staining and imaging of Candida species.