Structural peculiarities of new benzopyrylium dyes: X-ray, FT-IR, and DFT complex study

Abstract

The structures of three newly synthesized substituted 2-(4-X-phenyl)-benzopyrylium dyes were investigated by XRD and IR methods. The 4-X-phenyl group was represented by phenyl, 4-chlorophenyl, and 4-bromophenyl substituents. Hirshfeld surface analysis showed numerous types of strong and weak interfragmentary interactions in the crystalline 6,7-dihydroxy-4-methyl-2-phenylbenzopyrylium perchlorate monohydrate. Complex density functional calculations (DFT) were performed to analyze energetic properties, electronic structures, and reactivity descriptors of the dyes. To determine the halogen influence on these characteristics, the 4-fluorophenyl and 4-iodophenyl structures were also considered in DFT computations. The electrostatic potential isosurface indicates that the electrophilic interaction of the dyes with cations will occur over the oxygen atoms of the two hydroxyl groups, whereas the hydrogen atoms of these two hydroxyl groups are most active in reactions with nucleophiles. The analysis of the electrophilicity index indicates that the increase of the mass/size of the substituent in position 4 of the phenyl ring increases the electrophilic character of the considered flavilium cationic dyes.