Enhanced Emission in Self‐Assembled Phenyleneethynylene Derived π‐Gelators

Abstract Optical properties of π‐systems are of great significance for a wide range of applications in materials and biology. Aggregation and self‐assembly induced emission are one of such phenomena. Herein, the self‐assembly induced modulation of the emission of p‐phenyleneethynylene (PE) chromophores bearing linear achiral (1) or branched chiral (2) alkoxy chains is reported. Self‐assembled structures of both 1 and 2 from n‐decane exhibit enhanced emission with fluorescence quantum yield (Φ_F) values of 0.34 and 0.25, respectively, whereas these molecules are less‐emissive in chloroform (Φ_F = 0.02). Transmission electron microscopy and fluorescence microscopy studies reveal the formation of entangled blue‐emissive fibers for 1 and supercoiled helical blue‐emissive fiber bundles for 2. At higher concentrations (8.8 × 10⁻³ m for 1 and 23.6 × 10⁻³ m for 2) in n‐decane, intense blue‐emitting gels are formed. Significant shift in the emission toward longer wavelength can be seen from solution state to aggregates to the gel state. The wide‐angle X‐ray scattering and fluorescence data indicate that the interdigitated lamellar assembly with weaker π‐stacking and the resultant restriction of rotation of the PE chromophores are responsible for the enhanced emission of the self‐assembled gel state.