E.P.R. studies of the lowest excited triplet states of aromatic carbonyl molecules in mixed organic crystals

Mao, Shun; Hirota, Noboru

doi:10.1080/00268977400100301

Cited by 39 publications

(12 citation statements)

References 18 publications

(10 reference statements)

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“…[2] studies of the properties of the lowest excited triplet (T1) states of a series of aromatic carbonyl molecules. In order to supplement these studies we have investigated the temperature dependence of the phosphorescence spectra and lifetimes and the S 0-->T absorption spectra of the aromatic carbonyl molecules in mixed crystal systems.…”

Section: Introductionmentioning

confidence: 99%

Studies of the temperature dependence of the phosphorescence spectra and decay rates of aromatic carbonyl molecules in mixed organic crystals

Mao

Hirota

1974

Molecular Physics

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The temperature dependence of the phosphorescence spectra, decay rates and the So -->T2(3n ~r*) absorption spectra were studied for aromatic carbonyl molecules in mixed organic crystals. The energy separation, AET, between the %r~r* lowest excited triplet (7'1) states and the higher 3n~r* states (T2) was estimated for several systems from the temperature dependence of the phosphorescence spectra and decay rates. It was found that the decay rates of the aromatic carbonyl molecules in the mixed crystal systems studied are determined by (1) thermal population to the 3nTr* states and (2) increased radiationless transition rates at higher temperatures. INTRODUCTIONIn the two companion papers we have discussed the results of PMDR [1] and E.P.R.[2] studies of the properties of the lowest excited triplet (T1) states of a series of aromatic carbonyl molecules. In order to supplement these studies we have investigated the temperature dependence of the phosphorescence spectra and lifetimes and the S 0-->T absorption spectra of the aromatic carbonyl molecules in mixed crystal systems. The motives and the objectives of the present study are the following :(1) The magnetic and decay properties of the T 1 states of many aromatic carbonyl molecules were discussed in terms of the vibronic mixing of the 3~r~r* and 3nrr* states [1,3,4]. In order to discuss these properties quantitatively it is necessary to determine the energy difference (AET) between the 3rrrr* (T1) and the 3nrr* (T2) states of these systems. We have attempted to estimate AE r from S 0-->T absorption spectra and temperature dependence of the phosphorescence spectra and lifetimes.(2) In discussing the photochemical properties of the aromatic carbonyl molecules, Wagner et al. [5] suggested the possible role of the thermal equilibrium between the lowest 3rrrr* and the nearby 3nrr* states. Mixed crystal systems can provide information on such equilibrium processes.(3) The radiationless transition from the lowest excited triplet state has been the topic of wide theoretical and experimental investigations in the past decade [6]. Temperature dependence of the radiationless processes has been investigated experimentally [7,8] and theoretically [9], but the previously investigated systems were limited to aromatic hydrocarbons such as benzene [7] and naphthalene [8]. It seems desirable to obtain more data on the temperature Downloaded by [McGill University Library] at 11:15 03 December 2014

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Section: Introductionmentioning

confidence: 99%

Studies of the temperature dependence of the phosphorescence spectra and decay rates of aromatic carbonyl molecules in mixed organic crystals

Mao

Hirota

1974

Molecular Physics

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“…The opposite signs of the slopes for D and E imply that D 0 Ͻ0. We take ͉G 0 ͉ϭ8Ϯ1 cm Ϫ1 , based on empirical values 3,4,7,12 and theoretical estimates 14 for other benzaldehyde systems. Equation ͑3a͒ and the slopes for D then yield the energy gaps to the higher triplet state in the perprotonated guest, ⌬E T , that are summarized in Table III.…”

Section: A Zero-field Splittingsmentioning

confidence: 99%

“…For example, the zero-field splitting constants and the kinetic parameters of the lowest triplet state can vary significantly among similar derivatives and for a given derivative among different hosts. Such effects have been widely studied in aromatic aldehydes, [1][2][3][4][5][6][7][8][9] particularly for those cases wherein the lowest triplet state has * character. The variations in the properties of the 3 * state have been shown to arise largely from the changing energy denominators associated with the spin-orbit and other interactions with the nearby 3n* state.…”

Section: Introductionmentioning

confidence: 99%

Isotope effects and proton hyperfine interactions in the lowest 3nπ* state of substituted benzaldehydes

Neugebauer‐Crawford

Tinti

1995

The Journal of Chemical Physics

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The zero-field splittings, principal spin axes, kinetic parameters, and nuclear hyperfine interactions of the 3nπ* state of p-chloro- and p-methylbenzaldehyde and several of their deuterated derivatives are investigated by zero- and low-field optically detected magnetic resonance (ODMR) at 1.4 K in a p-dimethoxybenzene host. The zero-field splittings show large isotope effects. These are interpreted in terms of spin–orbit interaction with the nearby but higher lying 3ππ* state, yielding the energy gap between the two states in both benzaldehyde derivatives. The locations of the spin axes are approximately along the local symmetry axes of the carbonyl group and are insensitive to isotope. But, the spin axis most nearly normal to the plane of a host molecule deviates from the normal by an angle of 7°–13°. The kinetic parameters of the 3nπ* state also are relatively insensitive to isotope. The dominant hyperfine interactions are associated with the aldehyde hydrogen and indicate that the 3nπ* state is largely localized on the aldehyde moiety. Various properties of the 3nπ* and 3ππ* states are compared.

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“…The various interactions between these states are strongly modified by their energy gap, resulting in large variations in the fine structure splittings of the lowest triplet state among otherwise very similar systems. Substituted benzaldehydes appear particularly sensitive in this regard [1][2][3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Optical Zeeman and low-field ODMR studies of thenπ* phosphorescence ofp-chlorobenzaldehyde

Neugebauer

Tinti

1993

Molecular Physics

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The emissive triplet states ofp-chlorobenzaldehyde and p-chlorobenzaldehydedl as guests in p-dimethoxybenzene host crystals are investigated by optical Zeeman and low field optically detected magnetic resonance (ODMR) studies of their phosphorescence at ~< 4.2 K. The active spin level, the sign of the principal fine structure splitting constant, its magnitude and the approximate location of the fine structure axes are deduced from high-field Zeeman perturbations of the phosphorescence origins of the guests. ODMR measurements confirm the conclusions and yield better values for the constants and locations of the principal axes of the fine structure tensor. The results for the perprotonated guest show that D --3Z[2 = -0.58290 and'E =-(Y -X)/2 = -0"00714cm-1; the fine structure axes are oriented relative to the host with the y axis nearly normal to the molecular plane and the z axis rotated 40 ~ from the long molecular axis; and the phosphorescence arises predominantly from Tz. The d~-isotope of the guest has a larger magnitude for ]D] (~ 11%), but the other properties of its triplet state are similar to those of the perprotonated molecule. The results are interpreted in terms of a substitutional guest with a 3nn* assignment for the phosphorescent triplet state.

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E.P.R. studies of the lowest excited triplet states of aromatic carbonyl molecules in mixed organic crystals

Cited by 39 publications

References 18 publications

Studies of the temperature dependence of the phosphorescence spectra and decay rates of aromatic carbonyl molecules in mixed organic crystals

Studies of the temperature dependence of the phosphorescence spectra and decay rates of aromatic carbonyl molecules in mixed organic crystals

Isotope effects and proton hyperfine interactions in the lowest 3nπ* state of substituted benzaldehydes

Optical Zeeman and low-field ODMR studies of thenπ* phosphorescence ofp-chlorobenzaldehyde

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