Theoretical Investigation of Amino-Dichloro Chalcone Isomers. Part II: A DFT Structure-Stability Study of the FMO and NLO Properties.

The density functional theory (DFT) method using the functional hybrid (B3LYP) and 6-311G(d,p) basis set was utilized for the geometry optimization with dispersion correction, procedure (GO + DC), for the and chalcone isomers -1-(4-aminophenyl)- 3-(,-dichlorophenyl)prop-2-en-1-one, where () and () represent the positions of the two chlorine atoms [(2,3), (2,4),(2,5),(2,6),(3,4), and (3,5)] abbreviated (,)-chalcone, and 4-(,-dichloro-8a-chromen-2-yl)aniline, where ( = 5,6 and = 6,7,8,8a) abbreviated (,)-chromen isomers. The calculations revealed that chalcones are the most stable and the 4-(,-dichloro-8a-chromen-2-yl) aniline isomers are the least stable. The (3,5) chalcones were the most stable in both and chalcone series. However, the 4-(5,8a-dichloro-8a-chromen-2-yl) aniline is the most stable in the series. The isomer stability order is the same as in Part 1, in which the geometry optimization calculation was followed by the dispersion correction single point energy calculation (GO/SPDC) procedure. The procedures (GO + DC) and (GO/SPDC) were used to calculate energies of the highest occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO) and related properties. The order of the HOMO-LUMO energy gap (Δ ) was chromens < chalcones < chalcones. The lowest Δ was calculated for the (6,8)-chromen, while the highest energy gap was calculated for the (2,6)-chalcone, the least planar isomer. Among the chalcones, the (2,6)-has the highest , , Δ , hardness, and electronic chemical potential while possessing the lowest Mulliken electronegativity, electrophilicity index, ionization potential, and electron affinity. The (3,5)-isomer behaved oppositely. The chalcones have higher Δ than chalcones but follow the same trend as the series with regard to the . Among the chromens, the (5,8a)-chromen has the highest Δ , electron affinity, Mulliken electronegativity, hardness, and electrophilicity index but has the lowest and , and electronic chemical potential. (5,6)-Chromen was found to have the highest , electronic chemical potential, and lowest electron affinity. The highest is acquired by (6,8)-chromen; however, it has the lowest hardness value. The chromen isomers possessed the highest first-order hyperpolarizability due to being more planar and having longer π-conjugation than the other isomers. In contrast, the chalcones had the lowest hyperpolarizability. The HOMO and LUMO surfaces revealed intramolecular charge transfer in the and chalcones and chromens. Calculations of the molecular electrostatic potential showed that oxygen was the most negative. The HOMOs, LUMOs, and related properties mentioned above calculated according to the (GO + DC) and (GO/SPDC) procedures are in complete numerical agreement.