Tris(pentafluorophenyl)borane‐pyrrolo[3,2‐b]pyrrole Hybrids: Solid‐State Structure and Crystallization‐Induced Enhanced Emission

The work demonstrates that the quadrupolar nature of acceptor‐donor‐acceptor pyrrolo[3,2‐b]pyrrole systems can be substantially modified via the formation of boron‐nitrogen (B−N) bonds between peripheral CN groups and B(C6F5)3. This coordination enables a strong bathochromic shift of emission for both the solid crystalline state as well as in certain solvents. The B−N complex, or co‐crystal, was effectively isolated from the reaction between a pyrrolo[3,2‐b]pyrrole with two cyanophenyl moieties and tris(pentafluorophenyl)borane (TPFB), which were mixed in non‐polar solvents or prepared via liquid‐assisted solid‐state synthesis in a ball mill. An investigation of the structure‐property relationship confirmed that the intermolecular B−N bond influences the bathochromic shift in the absorption and emission spectra and that crystallization‐induced emission enhancement was observed owing to the benefits of the molecular packing style and the intermolecular C−H⋅⋅⋅F interactions. The postsynthetic strategy involves hybridization of molecules on a molecular level, which should provide a variety of novel photofunctional materials. Shine bright: Hybridization of a pyrrolo[3,2‐b]pyrrole dye with tris(pentafluorophenyl)borane via a boron‐nitrogen interaction is demonstrated. Structure‐property relationships at a molecular level revealed that the electronic perturbation of the dye induced by the boron‐nitrogen interaction leads to a bathochromic shift in the absorbance and fluorescence spectra in the solid state, in addition to the crystallization induced emission enhancement.