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[Display omitted] • Curcuminoids of boron difluoride have been synthesized. • Complexes studied by luminescence spectroscopy and DFT modeling. • Introduction of π-donor substituents increases luminescence quantum yield. • Dyes bio-imaging ability and cytotoxicity were investigated. Curcuminoids of boron difluoride, 1-aryl(hetaryl)-5-phenylpenta-2,4-dien-1-onates of boron difluoride, have been synthesized. A comparative study of the electronic structure, luminescent properties and their potential for applications in bio-imaging has been carried out. The influence of the electronic structure of α-substituents on the luminescence of compounds was studied by the methods of stationary and time-resolved luminescence spectroscopy and DFT modeling. The introduction of π-donor substituents leads to a noticeable bathochromic shift and an increase in the Stokes shift in the luminescence spectra. On going from σ-donor substituents in the phenyl ring to π-donor substituents, the luminescence quantum yield increases from 0.03 to 0.22. The maximum Stokes shift and high quantum yield of luminescence is exhibited by the complex with a stilbene substituent, which has the longest π-system and the maximum efficiency of charge transfer. Dyes are able to penetrate into the cells of the model cell line and accumulate, moreover, accumulation occurs mainly in the cytoplasm of cells. The compounds penetrate into the cells by 12 h of incubation without damaging it's structure and without causing rapid cell death. The submicromolar range of non-toxic concentrations during long-term incubation for a model cell line was determined, which is a characteristic of fluorescent imaging. Due to uniform distribution in the cytoplasm of cells dye with naphtyl substituent is promising for visualization of the cell cytoplasm. This leader compound has the lowest cytotoxicity for cells from the synthesized series of dyes, which makes it promising for further studies as a fluorescent imaging agent. The leader compound has the lowest cytotoxicity for cells from the synthesized series of dyes, which makes it promising for further studies as a fluorescent imaging agent. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two isomers of boron difluoride naphthaloylacetonates were synthesized. • Interrelation between crystal structure and luminescent properties has been revealed. • The complexes exhibited fluorescence, delay fluorescence and phosphorescence. • The role of the inversion of S 1 and T 2 levels in enhancing delay fluorescence is revealed. A comparative study of the luminescence properties of solutions and crystals of two isomers: boron difluoride 1-(1′-naphthyl)butanedionate-1,3 (α-NAcBF 2) and 1-(2′-naphthyl)butanedionate-1,3 (β-NAcBF 2) has been performed. An interrelation between the molecular and crystal structure of the studied complexes and their luminescence properties has been revealed. In the α-NAcBF 2 molecule, the plane of the naphthyl group was turned by 34.26° relatively to the chelate cycle, while the β-NAcBF 2 molecule was planar. The difference in the luminescence properties of the crystals of α-NAcBF 2 (452 nm) and β-NAcBF 2 (537 nm) was related to different abilities to form excimers. In β-NAcBF 2 crystals, J-aggregates consisted of dimers of antiparallel molecules comprising excimer traps. For the crystals and solutions of α-NAcBF 2 at 77 K, in addition to phosphorescence, the delayed fluorescence was observed. In case of β-NAcBF 2 , the delayed fluorescence was detected only for crystals, whereas the phosphorescence – for both crystals and solutions. [ABSTRACT FROM AUTHOR]