Vol. 24 No. 3 (2025): Mapana Journal of Sciences
Research Articles

Spectrophotometric Investigations of Charge Transfer Complexes formed between Imidazoles and DMAD

  • Pratibha Mittal,
  • Manisha Patni,
  • Raakhi Gupta
Pratibha Mittal
IIS (Deemed to be University), Jaipur
Manisha Patni
IIS (Deemed to be University), Jaipur
Bio
Raakhi Gupta
IIS (Deemed to be University), Jaipur
Bio

Published 2025-09-29

Keywords

  • Imidazole, DMAD, Formation Constant, Molar Extinction Coefficient, Standard Free Energy, Transition Energy

Copyright (c) 2025

Creative Commons License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Abstract

Four novel charge transfer (CT) complexes were synthesized between       imidazole-based donors and dimethyl acetylenedicarboxylate (DMAD) as the electron acceptor, in dichloromethane and acetone at room temperature. The formation of CT complexes was confirmed by characteristic n → π* and π → π* electronic transitions in the UV-Vis spectra. Stoichiometric analysis using Job's method revealed 1:1 and 2:1 donor–acceptor ratios for imidazole and N-methylimidazole, respectively. Among the synthesized complexes, those involving N-methylimidazole exhibited the highest formation constants (KCT), molar extinction coefficients (ε), and negative Gibbs free energy changes (ΔG⁰), indicating spontaneous and stable complexation. Additionally, the lowest CT transition energies (ECT) in dichloromethane confirmed stronger donor–acceptor interactions in this less polar solvent.

To further validate donor strength, DFT calculations were performed at the B3LYP/6-31+G(d) level. N-methylimidazole exhibited the highest HOMO energy, lowest HOMO–LUMO energy gap (ΔE), and the most favorable global reactivity descriptors—chemical softness and chemical potential—affirming its better electron-donating ability.

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