Optische Elektronenspin-Polarisation (OEP) in Triplett-Zuständen organischer Moleküle

1970 ◽  
Vol 25 (10) ◽  
pp. 1383-1394 ◽  
Author(s):  
H. Sixl ◽  
M. Schwoerer
Keyword(s):  
Spin Polarization ◽  
Lattice Relaxation ◽  
Microwave Emission ◽  
Spin Lattice Relaxation ◽  
Electron Spin Polarization ◽  
Zero Field ◽  
Triplet States ◽  
Spin Lattice ◽  
Optical Electron ◽  
Methyl Naphthalene

Abstract Stimulated microwave emission is observed in the ESR spectrum of 2-methyl-naphthalene and anthracene molecules in their triplet states at 4,2 °K. This is the consequence of a strong deviation from thermal equilibrium distribution within the three magnetic sublevels, a phenomenon called optical electron spin polarization (OEP). The OEP is due to spin selection rules either during the population or during the depopulation processes of the triplet states. In most cases both processes occour predominantly radiationless and are termed intersystem-crossing (ISC).In the present paper we report in detail about the kinetics of population, depopulation and spin-lattice relaxation of the phosphorescent triplet states of 2-methyl-naphthalene and anthra-cene. In addition the kinetical constants, the fine structure constants and the orientation in the host crystal of eleven different metastable triplet state molecules are presented in a table.As opposed to former investigations (quinoxaline, naphthalene, pyrazine) spin polarization in 2-methyl-naphthalene and anthracene is due to the selectivity of the depopulation mechanism. This is demonstrated by the time dependence of the ESR-signals after switching on and off ex-citation light. The evaluation of the experiments yields a common rule concerning the intrinsic zero-field decay rate constants of naphthalene, 2-methyl-naphthalene and anthracene:kx : ky : kz ≈ 2 : 1 : 0,2The selectivity of the population decreases in the sequence naphthalene, 2-methyl-naphthalene, anthracene.

scholarly journals P∩N Bridged Cu(I) Dimers Featuring Both TADF and Phosphorescence. From Overview towards Detailed Case Study of the Excited Singlet and Triplet States

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3415
Author(s):  
Thomas Hofbeck ◽  
Thomas A. Niehaus ◽  
Michel Fleck ◽  
Uwe Monkowius ◽  
Hartmut Yersin
Keyword(s):  
Quantum Yield ◽  
Decay Time ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Photo Luminescence ◽  
Delayed Fluorescence ◽  
Spin Lattice Relaxation ◽  
Zero Field ◽  
Triplet States ◽  
Spin Lattice

We present an overview over eight brightly luminescent Cu(I) dimers of the type Cu2X2(P∩N)3 with X = Cl, Br, I and P∩N = 2-diphenylphosphino-pyridine (Ph2Ppy), 2-diphenylphosphino-pyrimidine (Ph2Ppym), 1-diphenylphosphino-isoquinoline (Ph2Piqn) including three new crystal structures (Cu2Br2(Ph2Ppy)3 1-Br, Cu2I2(Ph2Ppym)3 2-I and Cu2I2(Ph2Piqn)3 3-I). However, we mainly focus on their photo-luminescence properties. All compounds exhibit combined thermally activated delayed fluorescence (TADF) and phosphorescence at ambient temperature. Emission color, decay time and quantum yield vary over large ranges. For deeper characterization, we select Cu2I2(Ph2Ppy)3, 1-I, showing a quantum yield of 81%. DFT and SOC-TDDFT calculations provide insight into the electronic structures of the singlet S1 and triplet T1 states. Both stem from metal+iodide-to-ligand charge transfer transitions. Evaluation of the emission decay dynamics, measured from 1.2 ≤ T ≤ 300 K, gives ∆E(S1-T1) = 380 cm−1 (47 meV), a transition rate of k(S1→S0) = 2.25 × 106 s−1 (445 ns), T1 zero-field splittings, transition rates from the triplet substates and spin-lattice relaxation times. We also discuss the interplay of S1-TADF and T1-phosphorescence. The combined emission paths shorten the overall decay time. For OLED applications, utilization of both singlet and triplet harvesting can be highly favorable for improvement of the device performance.

Optically Detected Spin Locking of Zero Field Electronic Triplet States and Cross Relaxation in the Rotating Frame

1975 ◽  
Vol 30 (3) ◽  
pp. 361-371 ◽  
Author(s):  
H. Schuch ◽  
C. B. Harris
Keyword(s):  
Magnetic Field ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Triplet States ◽  
Rotating Frame ◽  
Spin Lattice ◽  
Optically Detected ◽  
Spin Locking

The spin locking method known from NMR is shown to be useful also in ESR for investigating spin lattice relaxation problems and “slow” motions, e. g. questions of energy transfer by triplet states in organic molecular crystals, and probing of nuclear quadrupolar splittings even smaller than the ESR line width at zero magnetic field.Optically detected ESR spin locking experiments for isolated triplet states in zero field are demonstrated. It is shown how the complication of incoming and decaying triplet states and relaxation between all three triplet sublevels has to be handled during spin locking. An application, the study of the cross-relaxation between electronic triplet spin states and deuteron or proton spins is presented. These experiments are possible in spite of the first order quenching of the hyperfine coupling in zero magnetic field. Another application is briefly mentioned, in which the adiabatically demagnetized state in the rotating frame is used to probe the electronic triplet state transfer and nuclear spin lattice relaxation.

Spin–lattice relaxation in triplet states of isolated molecules and pure crystals in zero field

1978 ◽  
Vol 69 (9) ◽  
pp. 4319-4321 ◽  
Author(s):  
D. R. Lutz ◽  
K. A. Nelson ◽  
R. W. Olson ◽  
M. D. Fayer
Keyword(s):  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Zero Field ◽  
Triplet States ◽  
Spin Lattice ◽  
Isolated Molecules

scholarly journals P^N bridged Cu(I) Dimers Featuring both TADF and Phosphorescence. From Overview Towards Detailed Case Study of the Excited Singlet and Triplet States.

2021 ◽  
Author(s):  
Thomas Hofbeck ◽  
Thomas A. Niehaus ◽  
Michel Fleck ◽  
Uwe Monkowius ◽  
Hartmut Yersin
Keyword(s):  
Quantum Yield ◽  
Decay Time ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Photo Luminescence ◽  
Delayed Fluorescence ◽  
Spin Lattice Relaxation ◽  
Zero Field ◽  
Triplet States ◽  
Spin Lattice

We present an overview over eight brightly luminescent Cu(I) dimers of the type Cu2X2(PN)3 with X = Cl, Br, I and P^N = 2-diphenylphosphino-pyridine (Ph2Ppy), 2-diphenylphosphino-pyrimidine (Ph2Ppym), 1-diphenylphosphino-isoquinoline (Ph2Piqn) including three new crystal structures (Cu2Br2(Ph2Ppy)3, 1-Br, Cu2I2(Ph2Ppym)3, 2-I, and Cu2I2(Ph2Piqn)3, 3-I). However, we mainly focus on their photo-luminescence properties. All compounds exhibit combined thermally activated delayed fluorescence (TADF) and phosphorescence at ambient temperature. Emission color, decay time, and quantum yield varies over large ranges. For deeper characterization, we select Cu2I2(Ph2Ppy)3, 1-I, showing a quantum yield of 81 %. DFT and SOC-TDDFT calculations provide insight into the electronic structures of the singlet S1 and triplet T1 states. Both stem from metal+iodide-to-ligand charge transfer transitions. Evaluation of the emission decay dynamics, measured from 1.2 ≤ T ≤ 300 K, gives ∆E(S1-T1) = 380 cm-1 (47 meV), a transition rate of k(S1→S0) = 2.25×106 s-1 (445 ns), T1 zero-field splittings, transition rates from the triplet substates, and spin-lattice relaxation times. We also discuss the interplay of S1-TADF and T1-phosphorescence. The combined emission paths shorten the overall decay time. For OLED applications, utilization of both singlet and triplet harvesting can be highly favorable for improvement of the device performance.

Analysis of Spin Polarisation Transients in Periodically Photo-excited Triplet States

1975 ◽  
Vol 30 (5) ◽  
pp. 571-582 ◽  
Author(s):  
C. J. Winscom
Keyword(s):  
Lattice Relaxation ◽  
Rectangular Pulse ◽  
Decay Rates ◽  
Spin Lattice Relaxation ◽  
Pulse Excitation ◽  
Triplet States ◽  
Relaxation Rates ◽  
Spin Sublevel ◽  
Spin Lattice ◽  
The Individual

Abstract The behaviour of spin sublevel populations with time following periodic photo-excitation is ex-amined. The treatment is limited to conditions of magnetic field strength and temperature for which the spin lattice relaxation rates dominate the individual spin sublevel decay rates. The response of the system to three modes of excitation is considered: (i) continuous excitation using a time-independent intensity (ii) periodic rectangular pulse excitation and (iii) periodic waveform excitation. A convenient correspondence between the various forms of solutions is pointed out. The requirements of an experiment to determine spin-lattice relaxation rates in organic triplets at 77 K are discussed.

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.

Time Domain Zero Field NMR and NQR

1986 ◽  
Vol 41 (1-2) ◽  
pp. 440-444 ◽  
Author(s):  
A. Bielecki ◽  
D. B. Zax ◽  
A. M. Thayer ◽  
J. M. Millar ◽  
A. Pines
Keyword(s):  
Time Domain ◽  
Relaxation Times ◽  
Low Frequency ◽  
High Sensitivity ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Zero Field ◽  
Spin Lattice ◽  
Field Cycling ◽  
The Time Domain

Field cycling methods are described for the time domain measurement of nuclear quadrupolar and dipolar spectra in zero applied field. Since these techniques do not involve irradiation in zero field, they offer significant advantages in terms of resolution, sensitivity at low frequency, and the accessible range of spin lattice relaxation times. Sample data are shown which illustrate the high sensitivity and resolution attainable. Comparison is made to other field cycling methods, and an outline of basic instrumental requirements is given.

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.

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