Synthesis and photophysical properties of halogenated derivatives of (dibenzoylmethanato)boron difluoride.

A series of (dibenzoylmethanato)boron difluoride (BF2 DBM) derivatives with a halogen atom in one of the phenyl rings at the para-position were synthesized and used to elucidate the effects of changing the attached halogen atom on the photophysical properties of BF2 DBM. The room-temperature absorption and fluorescence maxima of fluoro-, chloro-, bromo- and iodo-substituted derivatives of BF2 DBM in THF are red-shifted by about 2-10nm relative to the corresponding peaks of the parent BF2 DBM. The fluorescence quantum yields of the halogenated BF2 DBMs (except the iodinated derivative) are larger than that of the unsubstituted BF2 DBM. All the synthesized compounds are able to form fluorescent exciplexes with benzene and toluene (emission maxima at λem =433 and 445nm, respectively). The conformational structure and electronic spectral properties of halogenated BF2 DBMs have been modeled by DFT/TDDFT calculations at the PBE0/SVP level of theory. The structure and fluorescence spectra of exciplexes were calculated using the CIS method with empirical dispersion correction.