Laser flash photolysis study of 2,6-dimethyl-3,5-diphenyl-4-pyrone and related chromones. Evidence for triplet state structural relaxation from quenching behaviors

Journal Article · Thu Oct 23 04:00:00 EDT 1986 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100280a103· OSTI ID:7169830

Bhattacharyya, K; Ramaiah, D; Das, P K; George, M V

The 308- or 337.1-nm laser excitation of 2,6-dimethyl-3,5-diphenyl-4-pyrone (1), 2-phenylchromone (2), and 2,3-diphenylchromone (3) results in the formation of short-lived triplets (tau/sub 0//sup T/ = 1-5 ..mu..s, lambda/sub max//sup T/ = 330-365 nm) in high yields (0.5-1.0 in benzene). From phosphorescence spectra at 77 K, the spectroscopic triplet energies of these aromatic enones are estimated at 69, 62, and 67 kcal mol/sup -1/, respectively. However, in fluid solutions at room temperature, the triplets are poorly quenched by 1-methylnaphthalene (E/sub T/ = 59.6 kcal mol/sup -1/), dienes (E/sub T/ approx. = 59 kcal mol/sup -1/), and ferrocene (E/sub T/ approx. = 40 kcal mol/sup -1/). In spite of the apparent exothermicity, the energy-transfer processes are inefficient; this suggests geometric distortion in these triplets, very probably in the form of partial twisting about the ene double bonds, causing a lowering of vertical energy (at relaxed geometry) by approx.30 kcal mol/sup -1/. The quenching behavior of the triplet of 2, however, is normal, the rate constants for quenching by the above-mentioned quenchers being in the limit of diffusion control. A major reason for the excited-state torsional distortion in 1 and 3 appears to be the steric interaction between adjacent substituents (phenyl and methyl) on the carbon atoms of the ene double bond.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 7169830
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 90:22; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400500* -- Photochemistry
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DE-EXCITATION
DECOMPOSITION
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EXCIMER LASERS
EXPERIMENTAL DATA
GAS LASERS
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
LASERS
LOW TEMPERATURE
LUMINESCENCE
MEDIUM TEMPERATURE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOSPHORESCENCE
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PYRANS
PYRONES
RADIATIONLESS DECAY
REACTION KINETICS
SPECTRA
STRUCTURAL CHEMICAL ANALYSIS
VISIBLE SPECTRA