Luminescent β-diketones (bdks) and difluoroboron complexes (BF2bdks) exhibit environment-sensitive properties in solution, aggregation-induced emission (AIE) and stimuli-responsive fluorescence in the solid state. A new set of 4-azepane-substituted β-diketone ligands (L-H, L-OMe, L-Br) and difluoroboron coordinated dyes (D-H, D-OMe, D-Br) were synthesized with a hydrogen (L-H, D-H), methoxy donor (L-OMe, D-OMe) or a bromide heavy atom acceptor (L-Br, D-Br) substituent in the 4'-position. Solvatochromism, viscochromism, AIE, mechanochromic luminescence (ML) and halochromism were investigated. Compared to the bdk ligands, the boronated dyes showed higher extinction coefficients but lower quantum yields and red-shifted absorption and emission in CH2Cl2. Computational studies showed that intramolecular charge transfer (ICT) dominated rather than π−π* transitions in all the compounds regardless of boron coordination. In solution, the bdk ligands and boron complexes exhibited red-shifted emission in more polar solvents and increased fluorescence intensity in more viscous media. Additionally, AIE properties of the compounds were measured in water/THF mixtures. While the emission of the bdk ligands was quenched upon aggregation, enhanced emission was observed for the boronated dyes, indicative of AIE. Solid-state emission properties, ML and halochromism, were also investigated utilizing spin cast films. For ML, smearing caused a bathochromic emission shift for L-Br, and powder X-ray diffraction (XRD) patterns indicate a crystalline to amorphous phase transition upon smearing. Halochromism experiments were performed using trifluoroacetic acid (TFA) and triethylamine (TEA) vapors. Large hypsochromic emission shifts were observed for all the bdk ligands and boron dyes after exposure to TFA vapor, and reversible fluorescence switching was achieved using the acid/base pair.

Luminescent azepane-substituted β-diketones and difluoroboron complexes

254th National Meeting (2017)

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