Computational Investigation of the Structural, Vibrational, and Optoelectronic Properties of DH4T: A DFT Study

In the present study, the structural, vibrational, electronic, and optical properties of DH4T were investigated using density functional theory. The optimized molecular structure and calculated vibrational spectra provide useful insight into the characteristic features of this conjugated quaterthiophene system. The calculated IR spectrum shows prominent bands in the low-, mid-, and high-frequency regions, including notable features around 1250 and 1600 cm⁻¹, while the Raman spectrum exhibits strong features near 1100 and 1500 cm⁻¹. These vibrational characteristics reflect the different stretching and bending motions of the conjugated molecular framework. The calculated UV-Vis spectrum shows a prominent absorption band around 450 nm, corresponding to an optical transition energy of approximately 2.76 eV. The frontier molecular orbital analysis gives HOMO and LUMO energies of -4.8232 and -1.7780 eV, respectively, resulting in a HOMO-LUMO energy separation of 3.0452 eV. The calculated global reactivity descriptors further provide information about the electronic character and chemical response of DH4T. The molecule also exhibits a dipole moment of 0.3912 Debye, indicating a relatively low overall molecular polarity.

1.                Roncali, J. Conjugated poly(thiophenes): synthesis, functionalization, and applications. Chemical Reviews 1992, 92, 711–738. 2.                McCullough, R. D. The chemistry of conducting polythiophenes. Advanced Materials 1998, 10, 93–116. 3.                Handbook/review reference specifically describing substituted oligothiophenes/quaterthiophenes should be added here if DH4T's experimental application is being discussed. 4.                Banwell, C. N.; McCash, E. M. Fundamentals of Molecular Spectroscopy, 4th ed.; McGraw-Hill, 1994. 5.                Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 6th ed.; Wiley, 2009. 6.                Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648–5652. 7.                Lee, C.; Yang, W.; Parr, R. G. Development of the Colle–Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785–789. 8.                Andersson, M. P.; Uvdal, P. New scale factors for harmonic vibrational frequencies using the B3LYP density functional method with the triple-ζ basis set 6-311+G(d,p). J. Phys. Chem. A 2005, 109, 2937–2941. 9.                Parr, R. G.; Pearson, R. G. Absolute hardness: companion parameter to absolute electronegativity. J. Am. Chem. Soc. 1983, 105, 7512–7516. 10.             Parr, R. G.; Szentpály, L. v.; Liu, S. Electrophilicity index. J. Am. Chem. Soc. 1999, 121, 1922–1924. 11.             Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; et al. Gaussian 09, Revision D.01; Gaussian, Inc.: Wallingford, CT, 2009.