Fluorescent properties and bioimaging potential of phenyl-substituted symmetrical furan diketopyrrolopyrroles

Abstract

Three symmetrical D-A-D systems of N-alkylated 3,6-difuran-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (EHDPP) with various π conjugated aromatic part based on furan moiety were designed, synthesised and fully characterised. These three different π-extended chromophores show different intramolecular charge transfer properties. Photophysical analysis of EHDPP derivatives revealed broad absorption in the 300–620 nm range, shifting absorption maxima by 60 nm with increasing π-conjugation. Emission studies showed intense fluorescence from 520 to 680 nm with 30–79 % quantum yields, which improved with increasing conjugation. The polarity of the solvent had minimal influence on the absorption spectra, but a slight positive solvatochromism was observed in the emission spectra, confirming the stabilised excited states with donor-acceptor characteristics. Low-temperature studies further revealed enhanced vibronic features and extended lifetimes, particularly for EHDPP-PF with 2-phenylfuran units, attributed to suppressing nonradiative processes. DFT analysis of molecular orbitals reveals increasing substituent contributions to HOMO and LUMO orbitals from furan to 2-phenylfuran, correlating with the enhanced donating ability of terminal groups. A preliminary biological study highlighted the potential of these derivatives as fluorescent cellular probes. The compounds exhibited strong fluorescence stability and negligible cytotoxicity at concentrations suitable for staining cellular compartments, making them promising candidates for biological imaging applications. These findings highlight the importance of terminal substituent modification in tuning the photophysical and electronic properties of EHDPP derivatives.