Insights and modelling on the nonlinear optical response, reactivity, and structure of chalcones and dihydrochalcones

For the first time, it is performed a discussion on the structure, reactivity, and nonlinear optical (NLO) response of new metabolites dihydrochalcone (4), 3,4,5-trimethoxychalcone (5), and 2,3,4,4'-tetramethoxydihydrochalcone (6) obtained by biotransformation of chalcone (1), 3,4,5-trimethoxychalcone (2), and 2,3,4,4'-tetramethoxychalcone (3) using Aspergillus flavus, an endophytic fungus naturally present in the Amazon Biome. Density Functional Theory methods associated with the 6-311++G(d,p) basis set and the Polarizable Continuum Model ensure either solvent contributions, as well as relevant quantum mechanical effects such as long-range and dispersion interactions. Usually, due to the environmental polarizability and the strong polar character inherent to the trans-isomer, such structure is dominating concerning the cis one. However, the vibrational analysis indicates that cis conformer prevails in 1, but the systematic inclusion of methoxy groups is the stabilizer factor for the trans structure in the chromophores 2 and 3. Moreover, the results also indicate that minimal structural changes have a severe impact on the electronic structure of the material. Essentially, the metabolic reaction substitutes alkene bonds in chalcones (1-3) by alkane bridges in dihydrochalcones (4-6), causing a strong hypsochromism (ca. 70 nm) in the UV-vis spectra and a reduction of the electrophilic power of the chromophores. Nevertheless, the inclusion of electron donor groups reverses this behavior and enhances the NLO response of the metabolites. In particular, the biotransformed chromophores can present static first-hyperpolarizability varying from 6.37 x 10(-30) to 59.35 x 10(-30) esu, which can be one hundred and sixty times greater than that reported for urea, a standard NLO material with beta(total) = 0.37 x 10(-30) esu. All chromophores are classified as moderate nucleophiles (2.0 <= N <= 3.0 eV) and strong electrophiles (omega > 1.5 eV). These results suggest that the biosynthesized chromophores have great reactivity, besides being promissory for optoelectronic and photonic applications. (C) 2021 Elsevier B.V. All rights reserved.