Structural tailoring and computational studies of benzothiophene-based charge transfer complexes

Charge transfer complexes including [HBT] and [FBT], 4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile with picric acid, and 2,4-dinitrophenol were synthesized by FTIR and 1H NMR. The full geometrical optimization, frontier molecular orbitals energies, energy gap, chemical reactivity indices, MEP maps, thermodynamic properties, the vibrational spectra, and partial density of states have been investigated at the DFT level (B3LYP) using the basis set SDD (Stuttgart/Dresden ECP plus DZ). Using the investigated computational analysis, it was concluded that the existence of H-bond beside charge transfer interaction is certainly responsible for the high stability of the formed CT complexes. The decrement of the HOMO-LUMO energy gap, a quantum chemical descriptor, explains the ease with which charge transfer interactions take place within the molecule. NBO explains the eventual hyper-conjugative interaction and charge delocalization that take place within the CT complexes and are responsible for the high optical nonlinearity of the HBT-PA, HBT-DNP, FBT-PA, and FBT-DNP complexes. NMR spectra reconfirmed the formation of the new compound, including both charge and hydrogen bonding. The nonlinear optical property and total dipole moment of the CT complexes reveal that the CT complexes could be a suitable candidate for nonlinear optical applications in optoelectronic devices.

Graphical abstract

The synthesized charge transfer complexes (HBT-PA, HBT-DNP, FBT-PA, and FBT-DNP) were characterized by FTIR, NMR, and DFT methods (B3LYP/SDD). Geometrical optimization, HOMO-LUMO energy gap, chemical reactivity, and NBO analysis confirmed charge transfer interactions and hydrogen bonding, enhancing optical nonlinearity. These complexes are promising for optoelectronic applications.