NIR Emission in Borondifluoride Complexes of 2′-Hydroxychalcone Derivatives Containing an Acetonaphthone Ring

We report the synthesis of borondifluoride complexes of a series of 2′-hydroxychalcone derivatives containing the hydroxynaphthone ring. TD-DFT calculations confirm the charge transfer character of the lowest-energy transition band and reveal large values for the ground-state dipole moment. The fluorescence emission spectra in the solid state are considerably red-shifted relative to those in solution, leading to maximum emission wavelengths spanning from the far red to the NIR. The emission properties are clearly characteristic of tightly packed chromophores with strong excitonic coupling, as confirmed by X-ray structure analysis and electronic absorption spectroscopy. The optical properties of the six dyes 1-BF 2 – 6-BF 2 are discussed in terms of interchromophoric interactions in the crystal and dipole moment values. Dyes 3-BF 2 and 4-BF 2 emit light at 690 and 751 nm with 13% and 6.5% efficiencies, respectively, and as such they represent very appealing materials. Compound 6-BF 2 presents an emission maximum wavelength at 804 nm with a fluorescence quantum yield value of 2%. This class of solid-state fluorophores may lead to exciting prospects for the generation of advanced materials.