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. B3PW91/6-311 + 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.

Zeolites as Adsorbents and Photocatalysts for Removal of Dyes from the Aqueous Environment

“…In the case of the MB, the Cl anion moved significantly to the plane corresponding to the central ring and shifted to interact with the nearby hydrogen atom noncovalently. In the case of the RB, the Cl anion practically remained in the vicinity of the positively charged nitrogen, which disagrees with the finding reported by Delgado and Selsby [ 65 ]. Namely, in their computational study, the Cl anion shifted towards the central part of the RB.…”

How an Eight-Membered Ring Alters the Rhodamine Chromophore

“…Such type of structure is created in the evolution of the system after electronic excitation, during which the rotation of phenyl rings is accompanied by intramolecular CT. A similar mechanism has been proposed for MG. 39 To gain further insights, we have extended our calculations to include R + Cl – ion pairs. The reason for this lies in that the calculation results of RB 42 show that the three orbitals of Cl – are energetically neighbor to the HOMO orbital located on R + . This also applies for the urea-bridged rhodamines in solvents of medium polarity ( Figure S5 ).…”

“…To gain further insights, we have extended our calculations to include R + Cl – ion pairs. The reason for this lies in that the calculation results of RB show that the three orbitals of Cl – are energetically neighbor to the HOMO orbital located on R + . This also applies for the urea-bridged rhodamines in solvents of medium polarity (Figure S5).…”

Understanding the Chemical Mechanism behind Photoinduced Enhanced Raman Spectroscopy

“…The measured HOMO level is consistent with previous measurements. ,, From the experimentally determined band diagram, there are no transitions possible from any of the occupied energy levels (oxygen vacancy state, valence band of TiO 2 , Fermi level of AgNPs, and HOMO of RhB) to unoccupied levels (conduction band of TiO 2 and LUMO of RhB) with a photon at 488 nm (2.54 eV), hence excluding a conventional LMCT/MLCT resonance Raman enhancement. Photoinduced electron transfer to RhB increasing the Raman polarizability: The final explanation for PIERS enhancement is a change in the intrinsic Raman cross-section of the chemisorbed molecule on the AgNP surface vs the cross-section of a nonchemisorbed molecule . The binding energies of three different adsorption geometries were calculated: Ag bonding via the amine functional group (RhB–amine–Ag), the stacking of the xanthene ring (RhB–xanthene–Ag), or the carboxyl group (RhB–carboxyl–Ag). − The binding via the carboxyl group is very unfavorable (Δ E ads = +13 eV), while the binding via the xanthene and amine groups are very close in terms of energetic stability (Δ E ads = −2 eV). …”

“…Photoinduced electron transfer to RhB increasing the Raman polarizability: The final explanation for PIERS enhancement is a change in the intrinsic Raman cross-section of the chemisorbed molecule on the AgNP surface vs the cross-section of a nonchemisorbed molecule . The binding energies of three different adsorption geometries were calculated: Ag bonding via the amine functional group (RhB–amine–Ag), the stacking of the xanthene ring (RhB–xanthene–Ag), or the carboxyl group (RhB–carboxyl–Ag). − The binding via the carboxyl group is very unfavorable (Δ E ads = +13 eV), while the binding via the xanthene and amine groups are very close in terms of energetic stability (Δ E ads = −2 eV).…”