Density Functional Theory Calculations on Rhodamine B and Pinacyanol Chloride. Optimized Ground State, Dipole Moment, Vertical Ionization Potential, Adiabatic Electron Affinity and Lowest Excited Triplet State

Abstract The ground state configuration of the gas phase cationic dyes pinacyanol chloride and rhodamine B are optimized with HF /6–311 + G(2d,2p) method and basis set. B3PW 91/6–311 + G(2df,2p) functional and basis set is used to calculate the Mulliken atom charge distribution, total molecular energy, the dipole moment, the vertical ionization potential, the adiabatic electron affinity and the lowest excited triplet state, the last three as an energy difference between separately calculated open shell and ground states. The triplet and extra electron states are optimized to find the relaxation energy. In the ground state optimization of both dyes the chloride anion migrates to a position near the center of the chromophore. For rhodamine B the benzoidal group turns perpendicular to the chromophore plane. For both dyes, the LUMO is mostly of π character associated with the aromatic part of the molecule containing the chromophore. The highest occupied MOs consist of three almost degenerate eigenvectors involving the chloride anion coordinated with σ electrons in the molecular framework. The fourth highest MO is of π character. For both molecules in the gas phase ionization process the chloride anion loses the significant fraction of electric charge. In electron capture, the excess charge goes mainly on the dye cation.