In developing high-performing conjugated polymers (CPs) for organic optoelectronics, a fundamental understanding about intrachain and interchain interaction is of vital significance. Here, we employ single molecule/aggregate spectroscopy, in conjunction with analyte systems with controlled structural features, to unmask the morphology and photophysics, as a function of intrachain and interchain interaction, from single polymer chain up to bulk state. The effect of side-chain and backbone structures on single polymer chain conformation was examined with single molecule polarization spectroscopy and theoretical simulations. The single chain spectra as well as fluorescence transients revealed that highly ordered single chain conformations, due to increased side-chain ordering and backbone rigidity, results in efficient electronic coupling along polymer chains. The tunable interchain morphologies, i.e., packing order and distance, were achieved through altering the ordering and size of side-chains, respectively, in aggregates self-assembled with solvent-vapor-annealing technique and then interrogated with polarization spectroscopy. Fluorescence blinking behavior and photon correlation measurement were employed to study the electronic coupling mechanism. Our data suggested highly ordered interchain packing is in favor of long-range interchain energy migration, while disordered packing, long interchain distance and competitive intrachain coupling significantly impede the interchain mechanism. In addition, we found that the fluorination of backbone can significantly enhance rigidity of single chains, and therefore leading to dominant intrachain electronic coupling and restrained interchain mechanism, despite of short interchain packing distance. Furthermore, the non-emissive excited states in CPs was studied with aggregates fabricated in a series of poor solvent media. The fluorescence experimental results combined with quantum chemical calculations suggested that there exists a crossing of energy levels of charge-transfer (CT) non-emissive and exciton emissive states as a function of solvent dielectric. Fluorescence decay dynamics indicated that the nonradiative CT-type states exist as a competitive channel of the formation of emissive exciton-type states.

Effect of intra- and interchain interaction on energy transfer in single conjugated polymers and aggregates

251st National Meeting (2016)

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