Transition dipole moment change through proton transfer in 2-mercapto-6-phenylpyridine-3-carbonitrile, computational chemistry study

Excitation energy transfer along molecular wires depends on the orientation of the transition dipole moments of the neighboring chromophores. This transition dipole moment is changed upon the proton transfer in the studied compounds. To this end, a quantum chemical characterization of 6-phenyl-2-thioxo-1,2-dihydropyridine-3-carbonitrile (2-mercapto-6-phenylpyridine-3carbonitrile) compound and its derivatives is performed using Density Functional Theory. The effect of the substitutions in the parent compound on the energy barrier between thiol and thione intraconversion as well as on the transition dipole moment was studied. The Intra-proton transfer (IMPT) process based on intrinsic reaction coordinate IRC calculations was energetically more favorable in the excited state (S1) than the ground state (S0) for all studied compounds. The effect of different substituents on the transition dipole moment orientation between thiol and thione was calculated. It was found that the electron withdrawing groups lead to high change in the transition dipole moment orientation through thiol/thione intra-conversion. The excited state energy transfer can be controlled by 20–100% depending on the orientation factor through the IMPT.