Structural Characteristics and Reactivity Relationship of some Thiophene Derivatives

ABSTRACT 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. Key words: Polarizability; photo-physical; excitation energy; oscillator strength; Time Dependent-Density Functional Theory