Studies of the Triplet State of Carbonyl Compounds. I. Phosphorescence of β-Diketones

Abstract

The phosphorescence intensity of the diketone form and of one of the two chelated enol forms of β-diketones in solution at 77°K depends largely on the solvent used. The phosphorescence of the diketone form (seen principally in polar solvent) is similar to that of aromatic monoketones and arises from a Tnπ* state. The phosphorescence of one of the two chelated enol forms in nonpolar solvent is emitted from a Tπ π* state as suggested by the external and internal heavy atom effects. However the shortness of the phosphorescence lifetime shows that the lowest triplet state is probably mixed with some higher energy triplet state of nπ* type. The diketone form seems much more luminescent than the chelated enol form. This result is consistent with the suggestion of Lamola [A. A. Lamola and L. J. Sharp, J. Phys. Chem. 70, 2634 (1966)] that a very fast radiationless decay takes place in molecules possessing an intramolecular hydrogen bond between the carbonyl oxygen and the hydroxyl hydrogen. The comparison of chelated enol spectra with those of crotonophenone and benzalacetone indicates that phosphorescent chelated enol has structure II, the other form being nonradiatively deactivated or nonexistent. Benzoyltrifluoroacetone gives a spectrum with a long lifetime which seems to originate from a nonchelated enol form.

Nature of the Ligand-Centered Triplet State in Gd3+β-Diketonate Complexes as Revealed by Time-Resolved EPR Spectroscopy and DFT Calculations

“…High-energy oscillators such as the C–H stretching mode have already been proven to cause lower phosphorescence yields and excited state lifetimes in similar organic compounds. 39 , 40 However, our DFT outcomes demonstrate that the mere presence of a high-energy oscillator is not enough to explain this behavior. Indeed, the P1 precursor and all ligands 1 – 3 feature C–H groups able to contribute to non-radiative decay, but they have different phosphorescence yields.…”

A new insight into the photochemistry of avobenzone in gas phase and acetonitrile from ab initio calculations

“…Despite the fact that AB has practical importance as an UVA filter, complete understanding of its photophysics and photochemistry is still missing due to solvent-dependent multiple relaxation pathways. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] AB is a b-dicarbonyl compound liable to keto-enol tautomerization. Many theoretical and experimental studies provided evidence that in the ground state the chelated enol form is favored due to the intramolecular hydrogen bond.…”

Diketone and UV based advanced oxidation/reduction technologies: molecular mechanisms and research advances

“…一样的光化学性质 [36][37][38][39] . 例如: 相比较丙酮, BD 拥有更 强的光谱吸收能力, 也更容易光裂解产生碳中心自由 基 [12] , 常被作为自由基链式反应的引发剂 [40] ; BD 激发 三重态的寿命非常长, 可达毫秒级别, 是少有的能够发 射磷光的脂肪酮类化合物, 其磷光(510 nm)量子产率 为 0.149 [41] .…”