Structural, optical spectroscopic, and density functional theory calculations of squaraine dye for organic electronic applications

Abstract The structural, optical spectroscopic, and density functional theory calculations of 2,4-Bis[4-(N,N-diisobutylamino)−2,6-dihydroxyphenyl] squaraine dye (SQ) are promising investigations that can be useful in photochemical mechanisms explanation and in designing promising chemosensors. The nature of the bonds, the chemical composition of SQ, crystallographic structure, morphology, and quality characteristics were explored by FTIR, XRD, and SEM investigations. The crystallite size, the dislocation density, and the lattice strain were found to be 57.3 nm, 3.045 × 10 −4 nm −2, and 3.065 × 10 −3 , respectively. The spectrum behavior of the absorbance and molar absorption coefficient spectra of SQ in DCM with three concentrations were analyzed to get some important optical properties of SQ dye. The determined optical gap transition equals <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> <mml:mi>a</mml:mi> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>o</mml:mi> <mml:mi>p</mml:mi> <mml:mi>t</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>1.81</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">eV</mml:mi> <mml:mo>.</mml:mo> </mml:math> Quantum chemical computations and optimized molecular geometries identified where electrophilic attacks are likely and analyzed the molecule’s electrostatic potential. Using DFT calculations at the B3LYP/6-31+G(d,p) level, the electronic structure of the squaraine molecule was confirmed, showing a HOMO–LUMO gap of 1.73 eV. MEP analysis indicated that the oxygen atoms are electron-rich, suggesting potential for hydrogen bonding and electrophilic interactions.