Solvatochromic A-D-A bithiophene derivative, steady state and time resolved studies and DFT calculations.

Document Type : Original Article


1 Department of chemistry, Faculty of Science, Alazhar University,

2 Department of Chemistry, Faculty of Science, Mansura University

3 Chemistry Department, Faculty of Science, Al-Azhar University, Cairo, Egyp

4 Department of chemistry, Faculty of Science, Alazhar University

5 Alkhalifa Almamoun


Steady state and time resolved properties of 5-(5-(4-fluorophenyl)thiophen-2-yl)thiophene-2-carboxamidine (FTTA) in a variety of solvents are reported. FTTA presents system of the type A-D-A (acceptor--bridge-donor-acceptor) where the bithiophene bridge acts as electron donor and the 4-fluorophenyl and amidine groups at both terminals act as electron acceptors. Solvent effect on the absorption spectra shows a slight solvent polarity dependence that covers a narrow range from 368 nm in cyclohexane to 379 in acetonitrile. On the other hand, change of the fluorescence emission maximum in aprotic solvents was only about 40 nm from acetonitrile to cyclohexane. The larger variation of the fluorescence emission maximum with the polarity of the solvent gives a conjecture that the nature of emission of from a state with intramolecular charge transfer character. However, the small dependence of the absorption maximum on the solvent polarity is attributed to a smaller dipole moment of the ground state than that of the excited state. Density functional theory (DFT) calculations shows a planar geometry in the excited state and non-planar geometry in the ground state. Dipole moments obtained from DFT and TD-DFT (Time-dependent density-functional theory) are also reported. Fluorescence lifetime, , and fluorescence quantum yield, f, were found to decrease with the emission energy, while the emission energy decreases as the solvent polarity increases. To ascertain the contributions of specific and non-specific solute-solvent interactions, we have utilized multi-parametric relationships as developed by Kamlet-Taft, Catalán, and Laurence. In every instance, it was discovered that non-specific interactions were largely dominating.