The metastable triplet state of zinc porphin and magnesium porphin: A study by E.S.R. in an n -octane crystal at 1·4 K

Articles you may be interested inAssessing the density functional theory-based multireference configuration interaction (DFT/MRCI) method for transition metal complexes Ground state electronic structures and spectra of zinc complexes of porphyrin, tetraazaporphyrin, tetrabenzoporphyrin, and phthalocyanine: A density functional theory study A combined quantum mechanics and molecular dynamics study of small Jahn-Teller distorted hydrocarbons: Another difficult test for density-functional theory

Section: Introductionsupporting

confidence: 84%

Jahn–Teller triplet excited state structures and spectra of zinc complexes of porphyrin and phthalocyanine: A density functional theory study

Nguyen¹,

Pachter²

2003

“…57͒ were used for zinc. A D 2h rectangular structure was obtained for ZnP triplet state, in agreement with experimental results 58,59 and earlier theoretical predictions. 60,61 We note that the D 4h square structure of the ground-state ZnP becomes a D 2h rectangle in the triplet state due to the JahnTeller effect.…”

Section: Computational Detailssupporting

confidence: 77%

“…2. Previous electron spin resonance studies 58,74,75 and electron nuclear double resonance work 59 indicated that the lowest triplet states for both porphyrins are of 3 B 2u symmetry, with the asymmetric direction defined by the two diagonal nitrogen atoms with larger separation ͑as shown in Fig. 2͒.…”

Section: B Intramolecular Triplet Energy Transfermentioning

confidence: 99%

The fragment spin difference scheme for triplet-triplet energy transfer coupling

You

Hsu

2010

To calculate the electronic couplings in both inter-and intramolecular triplet energy transfer ͑TET͒, we have developed the "fragment spin difference" ͑FSD͒ scheme. The FSD was a generalization from the "fragment charge difference" ͑FCD͒ method of Voityuk et al. ͓J. Chem. Phys. 117, 5607 ͑2002͔͒ for electron transfer ͑ET͒ coupling. In FSD, the spin population difference was used in place of the charge difference in FCD. FSD is derived from the eigenstate energies and populations, and therefore the FSD couplings contain all contributions in the Hamiltonian as well as the potential overlap effect. In the present work, two series of molecules, all-trans-polyene oligomers and polycyclic aromatic hydrocarbons, were tested for intermolecular TET study. The TET coupling results are largely similar to those from the previously developed direct coupling scheme, with FSD being easier and more flexible in use. On the other hand, the Dexter's exchange integral value, a quantity that is often used as an approximate for the TET coupling, varies in a large range as compared to the corresponding TET coupling. To test the FSD for intramolecular TET, we have calculated the TET couplings between zinc͑II͒-porphyrin and free-base porphyrin separated by different numbers of p-phenyleneethynylene bridge units. Our estimated rate constants are consistent with experimentally measured TET rates. The FSD method can be used for both intermolecular and intramolecular TET, regardless of their symmetry. This general applicability is an improvement over most existing methodologies.

“…21 That means that the Jahn-Teller effect ͑or the crystal field in previous interpretations 64,66 ͒ quenches the orbital angular momentum and splits the 3 E u state into two components ͑ 3 B 3u and 3 B 2u , as follows from our calculations, with the former state being the lowest component; the splitting ͑⌬ E ͒ must be so large that at 4.2 K only the lower 3 B 3u carries the Boltzmann population. These ideas are consistent with many experiments 17,21,67 on ODMR studies of phosphorescence of porphyrins without heavy metals and with their theoretical interpretations. 23,24,27 The ZFS of the phosphorescent triplet states of MgP and ZnP observed in ODMR experiments at 4.2 K proves almost identical to that of the freebase porphin, 67 in agreement with recent DFT calculations 24 which show that ZFS is determined by spin-spin coupling and SOC contribution is almost negligible.…”

Section: Phosphorescencesupporting

confidence: 78%

“…These ideas are consistent with many experiments 17,21,67 on ODMR studies of phosphorescence of porphyrins without heavy metals and with their theoretical interpretations. 23,24,27 The ZFS of the phosphorescent triplet states of MgP and ZnP observed in ODMR experiments at 4.2 K proves almost identical to that of the freebase porphin, 67 in agreement with recent DFT calculations 24 which show that ZFS is determined by spin-spin coupling and SOC contribution is almost negligible. 23,24 The EPR study of the T 1 state of PdP has provided a quite different situation.…”

Section: Phosphorescencesupporting

confidence: 78%

Theoretical study of phosphorescence in dye doped light emitting diodes

Minaev

Jansson

Ågren

et al. 2006

Phosphorescence of platinum͑II͒ octaethyl porphyrin ͑PtOEP͒, which has been used in organic light emitting diodes to overcome the efficiency limit imposed by the formation of triplet excitons, is studied by time-dependent ͑TD͒ density functional theory ͑DFT͒. The spin-orbit coupling ͑SOC͒ effects and the phosphorescence radiative lifetime ͑ p r ͒, calculated by the TD DFT method with the quadratic response technique, are analyzed for a series of porphyrins in order to elucidate the internal heavy atom effect on p r . While the significance of the d orbital admixture into the lowest unoccupied molecular orbital e g ͑ * ͒, proposed by Gouterman et al. ͓J. Chem. Phys. 56, 4073 ͑1972͔͒, is supported by our SOC calculations, we find that the charge-transfer ͑CT͒ mechanism is more important; the CT state of the 3 A 2g symmetry provides effective SOC mixing with the ground state, and a large 3 A 2g -3 E u transition dipole moment gives the main contribution to the radiative phosphorescence rate constant. The IR and Raman spectra in the ground state and first excited triplet state ͑T 1 ͒ are studied for proper assignment of vibronic patterns. An orbital angular momentum of the T 1 state is not quenched completely by the Jahn-Teller effect. A large zero-field splitting is predicted for PtP and PtOEP which results from a competition between the SOC and Jahn-Teller effects. A strong vibronic activity is found for the e g mode at 230 cm −1 in PtP phosphorescence which is shifted to 260 cm −1 in PtOEP. This out-of-plane vibration of the Pt atom produces considerable change of the SOC mixing. The role of charge-transfer state of d * type is stressed for the explanation of the electroluminescent properties of the dye doped light emitting diode.