Solvent-dependent spectral deconvolution of amino-substituted chalcones: UV–vis and FT-IR analysis supported by TD-DFT calculations

Abstract

• For the first time, spectral deconvolution was applied to aminochalcones in solvents of varying polarity using UV–vis and FT–IR techniques. • Para-aminochalcone exhibited the most pronounced bathochromic shift, indicating strong π-delocalization and solvent–solute interaction. • Solvent polarity was shown to modulate both π→π* and n→π* transitions, as well as key vibrational modes. • Gaussian and Lorentzian fitting allowed resolution of overlapping bands, revealing hidden transitions and vibrational substructures. • TD-DFT calculations supported the experimental findings, confirming the electronic nature of the observed spectral features. Solvents induce distinct conformational states in solute molecules, imparting similar characteristics to the crystalline structures observed in solid phases. The main underlying physicochemical mechanism is governed by dipole–dipole interactions. It has been demonstrated that the specific solvent environment further modulates the formation of the organic solid, particularly thin films, thereby impacting the functional efficiency of the resulting devices. Therefore, elucidating the structural modifications in the molecular conformation of solutes across different solvent environments provides a strategic roadmap for the rational design of devices with targeted functionalities. Since the electric dipole transition moment is a quantum mechanical property that quantifies the probability of electronic transitions between states of the solvent–molecule system, it plays a crucial role in understanding molecular spectroscopy. In this report, we present a detailed spectroscopic deconvolution analysis of chalcone, 3-aminochalcone, and 4-aminochalcone, with particular emphasis on the π → π * and n → π * electronic transitions, as well as the spatial gradient of the electric dipole moment probed by vibrational modes. The experimental approach involves spectroscopic measurements, including ultraviolet-visible (UV–Vis) spectroscopy to analyze electronic transitions and Fourier transform infrared (FT-IR) spectroscopy to probe the dipole moment gradients observed through vibrational modes. Additionally, the theoretical framework is based on time-dependent density functional theory (TD-DFT), employing a Hamiltonian that includes dipole–dipole interactions, along with a localized basis set of the def2-SVP type and the B3LYP functional. Solvent effects are modeled using the Conductor-like Polarizable Continuum Model (CPCM). Since electronic transitions and molecular vibrations involve quantum-statistical mechanisms, the spectral line shapes and broadening observed in the molecular spectra were analyzed by deconvoluting the bands using either Gaussian or Lorentzian profiles. Results revealed that the para-amino derivative showed significant bathochromic or red shifts (λ max ≈ 388 nm) and broader peaks, indicating enhanced π-delocalization. FT-IR analysis revealed vibrational band splitting and blue shift in the C=O and N–H regions, which align with resonance and hydrogen-bonding interactions. Through spectral deconvolution, we were able to resolve up to five electronic components for each compound, and TD-DFT calculations demonstrated a strong correlation with the experimental λ max . These findings suggest that amino substitution and solvent polarity work together to influence optical properties, highlighting their potential for designing optoelectronic materials.

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