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.