Structural Characteristics and Reactivity Relationship of some Thiophene Derivatives

Abstract

ABSTRACT<br /> The application of many hetero-aromatic compounds in pharmaceutical and dye industries make the theoretical study of their dipole moment (µ) oscillator strength (f) and other photo-physical properties worthwhile. These properties determine the solubility of many compounds; predict the relationship between their structures, properties and performance. The f, µ, α, transition dipole moment (∆µ), vertical Excitation Energies (EE) and the frontier orbitals energy gap (ΔELUMO-HOMO) of the optimized structures of 3, 4-diphenylthiophene (DPT); 3, 4-dicarboxylic-2, 5-diphenylthiophene (DCDPT); and benzo[b] thiophene (BT) were determined in solvents of different polarity functions (∆P) by Time-Dependent Density Functional Theory, using Becke's three parameter with Lee-Yang-Parr modification and 6-31G* basis set theory (TD- DFT- B3LYP/6-31G*). The associated quantum chemical descriptors of ΔELUMO-HOMO such as: Ionization Potential (IP) and global hardness (ƞ) for the compounds were also determined with the same level of theory. The µ of the molecules increases with increasing ∆P, but highest for DCDPT. Bathochromic shifts associated with decreasing EE were recorded for the electronic transitions in DCDPT compare with those observed for DPT and BT. The IP and ƞ increased as ∆P increases, suggesting high stability of these compounds in polar solvents. The energy gaps, its associated parameters and positive ∆µ suggested strong activity of the molecules, with DCDPT being the highest. This is in reasonable agreement with the experimental results for the molecules particularly if the experimental uncertainties are considered.<br /> <br /> Key words: Polarizability; photo-physical; excitation energy; oscillator strength; Time Dependent-Density Functional Theory