Turning Darkness into Light: Supramolecular Control of Emission in Push–Pull Chromophores

Abstract

Donor–acceptor chromophores based on 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) are promising materials for optoelectronic applications; however, their utility is often restricted by intrinsically weak fluorescence caused by efficient non-radiative decay pathways. Herein, we report a new series of donor-substituted, triazole-functionalized TCBD chromophores synthesized via a modular [2 + 2] cycloaddition–retroelectrocyclization approach. Systematic donor engineering at the triazole 4-position enables precise tuning of intramolecular charge transfer (ICT), aggregation behavior, and emissive properties. Although all chromophores exhibit broad ICT absorption bands and pronounced solvatochromism, the hydroxyl-functionalized derivative Tz-HEAP, featuring an AA–BB-type molecular arrangement, displays significantly enhanced fluorescence in CH3CN (ΦF = 4.9%) compared with the other analogues (ΦF = 0.2–0.3%). Concentration-dependent spectroscopic studies, supported by FE-SEM and AFM analyses, reveal the formation of emissive J-type nanoaggregates driven by cooperative π–π stacking and intermolecular hydrogen bonding. Electrochemical studies demonstrate strong electron-accepting characteristics of the TCBD core together with donor-dependent modulation of HOMO energies, resulting in progressive band-gap narrowing across the series. TD-DFT calculations further confirm efficient donor–acceptor electronic communication and dominant HOMO → LUMO charge-transfer transitions. Overall, this work establishes a clear structure–aggregation–property relationship and identifies hydrogen-bond-assisted aggregation as an effective molecular strategy for activating fluorescence in intrinsically non-emissive TCBD-based push–pull systems.