Solvent bandwidth dependence and band asymmetry features of charge-transfer transitions in N-pyridinium phenolates

Journal Article · Wed Apr 01 00:00:00 EST 1987 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00241a007· OSTI ID:6419120

Kjaer, A M; Ulstrup, J

They have investigated the shape of the solvatochromic absorption band for Betaine-26 2,4,6-triphenyl-N-(di-tert-butyl-4-hydroxyphenyl)pyridinium ion in a range of polar, apolar, protic, and aprotic solvents. Multiphonon band theory, including both molecular modes and a vibrationally dispersive solvent, indicates that the solvents fall in three categories: (1) The bandshape for polar, aprotic solvents is well reproduced by that for a structureless continuous dielectric and a single high-frequency molecular mode. Solvent broadening correlates with epsilon/sub o//sup -1/ - epsilon/sub s//sup -1/, epsilon/sub o/ being the optical and epsilon/sub s/ the static dielectric constant. The molecular frequency, Omega/sub c/, and displacement, ..delta../sub c/, are not very solvent dependent, emphasizing their molecular character, and the value Omega/sub c/ approx. = 1600 cm/sup -1/ suggests that C-O, C-N, and C-C stretching is involved. (2) Bands for apolar, aprotic solvents correspond to the same model. Omega/sub c/ and ..delta../sub c/ are again not very solvent dependent and coincide with the values for polar aprotic solvents. The solvent broadening is solvent independent, and wider than that for a structureless dielectric. This points to multipolar, dispersive, pressure, or pseudopotential forces as coupling mechanisms. (3) The bandshape for normal alcohols can only be produced by a model resting on two molecular modes and a vibrational high-frequency solvent tail. Broadening, asymmetry, molecular frequencies, and deuterium isotope effects trace the protic solvent spectral entanglement to coupling between betaine-26 and a local mode group with features of both O-H stretching and bending and of librational solvent motion.

• Research Organization: Technical Univ. of Denmark, Lyngby
• OSTI ID: 6419120
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 109:7
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
PHENOLATES
ELECTRON TRANSFER
PHOTOCHEMICAL REACTIONS
PYRIDINIUM COMPOUNDS
EXPERIMENTAL DATA
SOLVENTS
AMINES
AMMONIUM COMPOUNDS
AZINES
CHEMICAL REACTIONS
DATA
HETEROCYCLIC COMPOUNDS
INFORMATION
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIDINES
QUATERNARY COMPOUNDS
400500* - Photochemistry