Synthesis and photophysical properties of tricyclic boron compounds. Experimental and theoretical study

The one pot reaction of 5-formyl-2-furanboronic acid, arylamines (aniline, 2-aminoanthracene or 1-aminopyrene) and aminophenol derivatives (2-aminophenol, 2-amino-5-chlorophenol or 2-amino-5-nitrophenol) yielded tricyclic boronate species, involving an open furan ring process. The boron compounds obtained have a pi delocalized structural skeleton having photophysical properties. All seven compounds showed colorimetric properties in solvents with different dielectric constant, and the solvatochromic effect was denoted from the UV-vis spectra. Compounds also showed luminescence when irradiated with UV to 365 nm, nevertheless low fluorescence quantum yield in DMSO was observed (8-33%). Compounds present stability in DMSO solution up to for 96 h but degradation is recorded in THF solution in only 2.5 h. Computational studies were carried out using DFT/PBE1PBE for S-0 state and TD-DFT/PBE1PBE for S-1 state. The effect of solvent on transition wavelengths was simulated using the polarizable continuum model (PCM). It was observed that the substitution of the hydrogen atom by the chlorine atom stabilize the HOMO and LUMO levels, therefore, the transition energy values decrease for those orbitals in chlorophenol derivative compounds (3, 5 and 7), in comparison with the aminophenol analogues (2, 4 and 6). Furthermore, energy difference between the HOMO - LUMO orbitals decrease for structures having a major pi conjugation extension, thus, the band gap energy for pyrene and anthracene derivatives is smaller than in phenyl derivatives.