Phosphorescence of chloropentafluoroacetone at 77 °K

1970 ◽  
Vol 48 (18) ◽  
pp. 2937-2939 ◽  
Author(s):  
H. S. Samant ◽  
A. J. Yarwood
Keyword(s):  
Triplet State ◽  
Chlorine Atom ◽  
Rate Constants ◽  
Aliphatic Ketone ◽  
Radiative Rate

The phosphorescence of chloropentafluoroacetone at 77 °K is reported and the energy of the triplet state is estimated to be 74 kcal. The phosphorescence lifetimes and the relative phosphorescence yields of chloropentafluoroacetone and hexafluoroacetone at 77 °K were measured. The results show that substitution of a chlorine atom in the fluorinated aliphatic ketone changes the radiative and non-radiative rate constants from the triplet state at 77 °K by factors of about 1.7 and 2.3, respectively.

Photophysics of the lowest triplet state in 2-benzoylpyridine crystals. II. Optically detected e. p. r. in zero and high magnetic fields

1979 ◽  
Vol 369 (1737) ◽  
pp. 187-206 ◽  
Keyword(s):  
Triplet State ◽  
Rate Constants ◽  
Radiative Decay ◽  
Dynamic Properties ◽  
Deep Trap ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Zero Field ◽  
Spin Lattice ◽  
Optically Detected

Optically detected zero-field resonance has been used to characterize the intrinsic and deep trap 3 nπ * states in single crystals of 2-benzoylpyridine at 4.2 K. The dynamic properties of these states were studied by means of time-resolved modulated phosphorescence (t. r. m. p.) and estimates for the rate constants for depopulation and spin-lattice relaxation of the magnetic sub-levels obtained by computer simulation. For all species, depopulation from ז z dominates, having rates of order 100 s -1 , but the ז x and ז y sub-states have substantial radiative activity. The orientations of the fine-structure tensors of the magnetic species were determined from high-field e. p. r. spectra. Assuming that z is parallel to C = O, excitation causes the C = O direction to change by 8 ± 2° for the intrinsic species and by an in-significant amount for the deep trap. These spectra also demonstrated that the intrinsic triplet state is mobile. This species is believed to be a polaron with slow intersite hopping rate. A maximum energy transfer rate of 10 4 -10 5 s -1 was found for transfer between translationally inequivalent sites symmetry-related by twofold rotation about the crystal b -axis. Rate estimates for transfer to the other two translationally inequivalent sites established the two dimensional nature of the polaron. The sign and shape of the zero-field resonances for the intrinsic species were found to depend on whether excitation was through S 1 or T 1 . From the parameters required to simulate the corresponding t. r. m. p. signals it is inferred that the changes are largely due to differences in the rate constants for non-radiative decay. The deep trap was shown to have an orientation and magnetic properties similar to those of the intrinsic species, and is believed to be a physical defect. It has radiative activity from the ז x sub-level which is significantly less than for the intrinsic species. Spin-lattice relaxation is fast for the mobile intrinsic species ( ca . 10 4 s -1 ) compared with the deep trap rate ( ca . 50 4 s -1 ). For the intrinsic species a field dependence for spin-lattice relaxation is apparent.

Optische Spin-Polarisation im Triplett-Zustand von Naphthalin

1969 ◽  
Vol 24 (6) ◽  
pp. 952-967 ◽  
Author(s):  
M. Schwöhrer ◽  
H. Slxl
Keyword(s):  
Triplet State ◽  
Spin Polarization ◽  
Rate Constants ◽  
Uv Light ◽  
Lattice Relaxation ◽  
Stimulated Emission ◽  
Spin Lattice Relaxation ◽  
Spin Component ◽  
Triplet States ◽  
Selection Rules

Naphthalene, which is excited into the lowest triplet state by unpolarized UV-Iight shows a strong deviation from the Boltzman distribution within the three magnetic sublevels, which is ob­served by ESR. We call this deviation optical spin polarization. In the mixed crystal C10D8: 0.2% C10H8 , where the undeuterated Naphthalene acts as trap at 4.2 °K, the optical spin polarization exceeds the thermal spin polarization such that a steady state inversion between two of the mag­netic sublevels appears. This results in an emissive ESR-transition (stimulated emission of micro- waves). The time dependence of the spin polarization after switching on or off the UV-light is described by a superposition of two exponential functions with different rate constants. - The optical spin polarization is due to spin selection rules for the intersystem crossing process (ISC). These involve primarily the molecular symmetry. - The experimental results of the present paper are these selection rules for the pumping processes: The metastable triplet state is populated via the spin component τx.The depopulation rate constants of the three spin components τx, τv and τz are kx = 0.65 sec-1, ky=0.4 sec-1 and kz=O.15 sec-1 .The spin lattice relaxation probabilities are of the order of 1 sec-1. The latter are dependent on the direction of the magnetic field and on the concentration of the populated triplet states. - These results are compared with a theory of ISC.

Triplet-State Electron Spin Resonance of Chlorophyll a and b Molecules and Complexes in PMMA and MTHF. I: Experimental Determination of Fine-Structure and Rate Constants

1978 ◽  
Vol 33 (1) ◽  
pp. 83-93 ◽  
Author(s):  
W. Hagele ◽  
D. Schmid ◽  
H. C. Wolf
Keyword(s):  
Triplet State ◽  
Chlorophyll A ◽  
Rate Constants ◽  
Resonance Field ◽  
Zero Field ◽  
Chlorophyll B ◽  
Low Concentrations ◽  
Spin Resonance ◽  
Chlorophyll A And B

The triplet state zero-field splittings and the rate constants for the population and depopulation of the triplet spin sublevels have been investigated for chlorophyll a and chlorophyll b in polymethylmethacrylate (PMMA) and methyltetrahydrofurane (MTHF) as a function of the concentration. In PMMA both chlorophyll a and chlorophyll b yielded only one ESR spectrum in the entire range of concentration which could be covered (1.5 × 10-5 - 1 × 10-3 mole/1). In MTHF the results were more complicated. At low concentrations (up to 103 mole/1) only one spectrum was observed, at higher concentrations additional spectra were detectable (all together two for chlorophyll a and five for chlorophyll b at 10-1 mole/1). The assignment of these spectra was facilitated by observing the "triplet resonance-field identity" which connects the resonancefield strengths for the canonical orientations of one particular species. Furthermore, the rate constants for some of these species could be determined.

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