Design of Highly Fluorescent Imidazole-Based Metal-Free D-Π-A Dye for DSSC Application.

Abstract

In this study, the photophysical, electronic, and optoelectronic properties of 1-(4-methoxyphenyl)-2-(4-nitrophenyl)-4,5-diphenyl-1H-imidazole (DS-1) were investigated using a combination of experimental and theoretical approaches. The surface morphology of DS-1 was analysed using Scanning Electron Microscopy (SEM), revealing a rod-like structure with non-uniform distribution, while Energy Dispersive X-ray Analysis (EDAX) confirmed its elemental composition. Solvatochromic studies demonstrated a significant bathochromic shift in absorption and fluorescence maxima with increasing solvent polarity, indicating enhanced excited-state stabilization through solute-solvent interactions. A notable Stokes shift in hydrogen-bonding solvents highlighted strong intramolecular charge transfer (ICT) effects. The ground and excited-state dipole moments were estimated using solvatochromic correlations, revealing a higher dipole moment in the excited state, confirming significant electronic redistribution upon excitation. Mulliken atomic charge analysis further supported solvent-induced electronic polarization, with DMSO showing the highest charge redistribution due to strong solute-solvent interactions. Frontier Molecular Orbital (FMO) analysis revealed a HOMO-LUMO gap of 3.149 eV, suggesting absorption in the UV-visible region. Global Chemical Reactivity Descriptors (GCRD) were used to estimate chemical hardness, electrophilicity, and nucleophilicity, indicating the potential optoelectronic stability of DS-1. To explore practical applications, DS-1 was incorporated as a sensitizer in Dye-Sensitized Solar Cells (DSSCs). The fabricated DSSC exhibited a moderate power conversion efficiency (PCE) of 1.75%, with an open-circuit voltage (V_oc) of 653.3 mV, short-circuit current density (J_sc) of 4.74 mA/cm², and a fill factor (FF) of 56.73%. The findings suggest that structural modifications, such as π-conjugation extension and donor-acceptor engineering, could improve light absorption and charge transport properties, making DS-1 a promising candidate for optoelectronic and photovoltaic applications.