Time-resolved ESR detection of the phosphorescent states of xanthone in glassy matrixes at 77 K

Abstract

The excited triplet states of xanthone in organic glasses are studied by using a time-resolved ESR method at 77 K. The observed spectra are found to be superpositions of three kinds of triplet states in polar media. The mixing ratio of the three spectra varies with the change of the solvent. The spectrum that shows a small zero-field splitting parameter D becomes predominant in water-containing solvents and is assigned to a purely isolated 3 * state influenced by a strong hydration due to water molecule impurity. The other two spectra are assigned to the 3irx* states having large D values, which are strongly coupled through spin-orbit interaction with the 3 * state located a little higher in energy. The existence of these two 3inr* states in dry polar glasses may be attributed to structurally different conformers in the inhomogeneous circumstance of the glassy condition. In nonpolar glasses, no excited triplet state of xanthone is observed when an X-band ESR spectrometer is used because of its huge D value, but a weak total emissive signal of the excited 3 * of hydrated xanthone existing as an impurity is detected.

On the unusual fluorescence properties of xanthone in water

“…This relies on the fact that ISC often does not distribute population evenly among the substates of one triplet (usually referred to as T x , T y , and T z ). 30 For xanthone such a preferential population of the T z by a factor of 5-10 was inferred from ESR 29 and ODMR spectroscopy. 5 The ESR spectroscopy, however, was performed on 3 pp*.…”

“…Singlet-triplet splitting is known to be small for np* states and high for pp* states, 3 which implies that the lowest triplet state in polar media is of pp* character. In fact, the phosphorescence spectrum and lifetime measurements 4 as well as ESR spectroscopy 29 of the xanthone triplet in polar media indicate that the lowest triplet state is of pp* nature. The phosphorescence experiment 4 places the triplet 3 pp* state about 3300 cm À1 below the singlet 1 pp* state-an energy gap by far too large to account for the observed delayed fluorescence.…”

“…Absorption spectra of the relaxed triplet state of xanthone vary with the solvent polarity. 22 In polar solvents in which the lowest triplet state is of 3 pp* character 4,29 the absorption peaks around 610 nm. In nonpolar solvents where the 3 np* and 3 pp* states are in energetic vicinity 8 two absorption bands are observed.…”

Time-resolved ESR study on photochemical formation of radical pair in cyclodextrin cavities

“…Figures la, b, and c show the TRESR spectra observed in the photolysis of the frozen aqueous solution of Xn and respective CDs at 77 K. These spectra were assigned to the excited triplet state of Xn (12). The differences in these spectra reflect the different environments in the respective CD cavities.…”

S1 1A2(nπ*) and S2 1A1(ππ*) States of Jet-Cooled Xanthone

“…[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] It is necessary to investigate isolated molecules in order to fully understand the energy structure and the mechanism of dynamical processes. In this article we present the results of phosphorescence excitation spectrum of jet-cooled xanthone.…”