Understanding the Stokes shift and nonlinear optical behavior of 1-nitro-2-phenylethane: A sequential Monte Carlo/Quantum Mechanics discussion

Synthesis, Biotransformation, Characterization, and DFT Study of Organic Azachalcone Dyes and Secondary Metabolites with Biological and Conformation Dependence of Dipolar-Octupolar NLO Responses

Chalcones are organic chromophores with diverse biological applications and potential for use in various electronic devices due to their recognized optical properties. This research focuses on the organic synthesis, FT-NMR characterization, and biotransformation of three azachalcones (1-3) using the Exserohilum rostratum fungus, yielding novel compounds (1a-3a). In vitro biological assays against Gram-positive and Gram-negative bacteria revealed promising pharmacological potential for these new chromophores. A key structural difference, the interchange of an HC = CH bond by a H2C-CH2 bond, significantly impacts biological and electronic properties. For instance, while biotransformed 1a exhibits similar activity to tetracycline and amoxicillin, compounds 2a and 3a demonstrate a 4-fold and thirty-fold increase in inhibitory activity against Gram-negative E. coli, respectively, compared to their parent compounds. Density functional theory calculations suggest that the biotransformation reaction reduces the refractive index (n), which may limit its applicability in certain light-handling applications. However, Hyper-Rayleigh scattering calculations indicate that these chromophores exhibit higher nonlinear optical (NLO) responses compared to standard NLO materials such as urea and p-nitroaniline, making them promising candidates for photonic and optoelectronic devices, such as nanostructured circuits. Interestingly, while the original molecules exhibit a dominant dipolar (Φ J=1) NLO response, the biotransformed compounds, as stable isomers, display a predominant octupolar (Φ J=3) architecture. These findings highlight the potential of these novel compounds for biotechnological and optoelectronic applications.

Elucidating the Photophysics and Nonlinear Optical Properties of a Novel Azo Prototype for Possible Photonic Applications: A Quantum Chemical Analysis

The photophysics and nonlinear optical responses of a novel nitrothiazol-methoxyphenol molecule were investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods with the polarizable continuum model to take the solvent effect into account. Special attention is paid to the description of the lowest absorption band, characterized as a strong π → π* state in the visible region of the spectrum. The TD-DFT emission spectrum analysis reveals a significant Stokes shift of more than 120 nm for the π → π* state in gas phase condition. The results show a great influence of the solvent polarity on the nonlinear optical (NLO) response of the molecule. Specifically, the second harmonic generation hyperpolarizability β(-2ω; ω, ω) shows a large variation from gas to aqueous solvent (82 × 10-30 to 162 × 10-30 esu), exhibiting notably higher values than those reported for standard compounds such as urea (0.34 × 10-30 esu) and p-nitroaniline (6.42 × 10-30 esu). Furthermore, a two-photon absorption analysis indicates a large cross-section (δ2PA = 77 GM) with superior performance compared to several dyes. These results make the molecule quite interesting for nonlinear optics.

Calculation of the geometry, absorption spectrum, and first hyperpolarizability of 4,5-dicyanoimidazole derivatives in solution. A multiscale ASEC-FEG study

We investigate the effects of solvents on the geometry, absorption spectrum, and first hyperpolarizability of six push-pull molecules, each containing a 4,5-dicyanoimidazole group as an electron acceptor and a N,N-dimethylamino group as an electron donor, with systematically extended π-conjugated systems. Geometry optimizations in dichloromethane, methanol, water, and formamide under normal thermodynamic conditions were performed using the average solvent electrostatic configuration-free energy gradient method, which employs a discrete solvent model. The conformational structure of molecules is moderately affected by the environment, with the π-conjugated system becoming more planar in protic solvents. Solvent effects on the first hyperpolarizability result in marked increases that are in line with the red shifts of the absorption spectrum. The hyperpolarizability of smaller molecules within the set may be significantly influenced by the effects of geometry relaxation in highly polar protic solvents. The results illustrate the role of hydrogen bonds in the structure and electronic properties of push-pull molecules in protic environments. For smaller molecules, hydrogen bonds significantly contribute to enhancing the hyperpolarizability, but the effect of these specific interactions becomes less significant with the length of the π-conjugated system.