Symmetry-directed supramolecular assembly and tunable optical response of a perylene diimide derivative

We report a comparative study on two N-substituted perylene diimide (PDI) derivatives, PDI-1 (symmetric) and PDI-2 (asymmetric), to investigate their photophysical and self-assembly behaviour in solution phase. UV–vis spectra of PDI-1 showed sharp vibronic bands at 455, 485, and 520 nm, while PDI-2 exhibited broadened, blue-shifted absorption with Mie scattering beyond 550 nm, indicating aggregation. Fluorescence studies revealed monomeric emission for PDI-1 (λ_em ≈535, 570, 620 nm) and H-type aggregation for PDI-2 (λ_em ≈527, 560 nm), with a critical aggregation concentration (CAC) of ~5.2 µM. DLS confirmed larger aggregates in case of PDI-2 (~385 nm) than that witnessed for PDI-1 (~89 nm). DFT analysis (B3LYP/6–31 G*) showed comparable HOMO–LUMO gaps (0.93 vs 0.98 eV), indicating that the structure–property insight is valuable for designing PDI-based nanomaterials in sensing, photovoltaics, and optoelectronics. The study establishes molecular design principles to control aggregation, morphology, and functional performance in perylene-based organic semiconductors.