Divergent Excitons by Programming Secondary Structures of Perylene Bisimide Oligomers

Deliberate control of exciton landscapes in π-conjugated oligomers represents a powerful approach to advancing functional optoelectronic materials, yet systematic modulation within homo-oligomeric architectures remains highly challenging. Here, we present two series of homo-perylene bisimide (PBI) oligomers in which contrasting bay-substitution patterns dictate the secondary structures (molecular conformation), inter-PBI coupling, and exciton behavior. The conformationally less defined zigzag PBI1 oligomers retain Frenkel-type emission in nonpolar environments but undergo polarity-induced symmetry-breaking charge separation (SBCS) in polar solvents, generating charge-separated states with chain-length-dependent dynamics. In sharp contrast, the π-stacked PBI2 oligomers exhibit strong H-type coupling, in which Frenkel excitons rapidly evolve into excimer-like charge-resonance states and multiexciton configurations that partially relax into triplets. Resonance Raman spectroscopy reveals distinct vibrational fingerprints, distinguishing structurally isolated PBI units in PBI1 oligomers from strongly coupled H-type aggregates in PBI2 oligomers, thereby providing direct structural evidence for their divergent inter-PBI interactions. Ultrafast spectroscopy under varied solvent and temperature conditions, supported by electronic-structure calculations, further demonstrates how substitution patterns govern the contrasting exciton dynamics. Collectively, the results establish secondary-structure programming as a rational design principle for tuning exciton diversity in homo-oligomers, bridging biological paradigms of chromophore organization with synthetic strategies for light harvesting, photocatalysis, and optoelectronics.