Selectivity Control in Electron Spin Inversion Processes:  Regio- and Stereochemistry of Paternò−Büchi Photocyclo- additions as a Powerful Tool for Mapping Intersystem Crossing Processes

2004 ◽  
Vol 37 (12) ◽  
pp. 919-928 ◽  
Author(s):  
Axel G. Griesbeck ◽  
Manabu Abe ◽  
Samir Bondock
Keyword(s):  
Electron Spin ◽  
Intersystem Crossing ◽  
Selectivity Control ◽  
Spin Inversion

Trifluoromethylphenylcarbenes. Carbene-Carbene Interconversion on the Singlet Energy Surface and Rearrangement to Trifluorobenzocyclobutene, Trifluorostyrene, and Trifluoromethylfulvenallenes

2015 ◽  
Vol 68 (1) ◽  
pp. 36 ◽  
Author(s):  
Rodney J. Blanch ◽  
Curt Wentrup
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Esr Spectroscopy ◽  
Energy Surface ◽  
Esr Spectra ◽  
Intersystem Crossing ◽  
Triplet States ◽  
Long Wavelength ◽  
Spin Resonance ◽  
Triplet Carbenes

The four isomeric α-, ortho-, meta-, and para-trifluoromethylphenylcarbenes were generated by photolysis of the corresponding 3-phenyl-3-trifluoromethyldiazirene 1 or the four isomeric trifluoromethylphenyldiazomethanes 2 and 4–6. The four corresponding triplet trifluoromethylphenylcarbenes 3 and 7–9 were observed by electron spin resonance (ESR) spectroscopy in Ar matrices at 14 K. The α- and ortho-carbenes 3 and 7 and the ortho- and para-carbenes 7 and 9 interconvert partially when generated by short-wavelength photolysis (350 nm) before intersystem crossing to the triplet states. The triplet states do not undergo further Carbene-Carbene interconversion. The interconversions are assumed to take place via the meta-trifluoromethylphenylcarbene 8. When the ortho- and para-carbenes are generated by long-wavelength photolysis (>450 nm), the discrete, non-interconverting triplet carbenes are observed in the ESR spectra. Flash vacuum thermolysis of the diazirene 1 at 500°C afforded a mixture of bis(trifluoromethyl)heptafulvalenes 11, bis(trifluoromethyl)stilbenes 12, and bis(trifluoromethyl)anthracenes 13, and the presence of their likely precursor(s), trifluoromethylcycloheptatetraene(s), was confirmed by a peak at 1830 cm–1 in the Ar matrix IR spectrum. In addition, at 700°C, four monomeric carbene rearrangement products were isolated and characterised, viz. 1,1,2-trifluorobenzocyclobutene 14, 1′,2′,2′-trifluorostyrene 15, and 1- and 2-trifluoromethylfulvenallenes 16 and 17.

Understanding and Controlling Intersystem Crossing in Molecules

2021 ◽  
Vol 72 (1) ◽  
Author(s):  
Christel M. Marian
Keyword(s):  
Electron Spin ◽  
Transition Probabilities ◽  
Relativistic Quantum ◽  
Spin Coupling ◽  
Annual Review ◽  
Publication Date ◽  
Intersystem Crossing ◽  
Light Emitting ◽  
Interaction Terms ◽  
Spin Spin Coupling

This review article focuses on the understanding of intersystem crossing (ISC) in molecules. It addresses readers who are interested in the phenomenon of intercombination transitions between states of different electron spin multiplicities but are not familiar with relativistic quantum chemistry. Among the spin-dependent interaction terms that enable a crossover between states of different electron spin multiplicities, spin–orbit coupling (SOC) is by far the most important. If SOC is small or vanishes by symmetry, ISC can proceed by electronic spin–spin coupling (SSC) or hyperfine interaction (HFI). Although this review discusses SSC- and HFI-based ISC, the emphasis is on SOC-based ISC. In addition to laying the theoretical foundations for the understanding of ISC, the review elaborates on the qualitative rules for estimating transition probabilities. Research on the mechanisms of ISC has experienced a major revival in recent years owing to its importance in organic light-emitting diodes (OLEDs). Exemplified by challenging case studies, chemical substitution and solvent environment effects are discussed with the aim of helping the reader to understand and thereby get a handle on the factors that steer the efficiency of ISC. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 72 is April 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Electron spin dynamics in excited state photochemistry: recent development in the study of the intersystem crossing and charge transfer in organic compounds

2021 ◽  
Author(s):  
MUHAMMAD IMRAN ◽  
Xue Zhang ◽  
Zhijia Wang ◽  
Xi Chen ◽  
Jianzhang Zhao ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Organic Compounds ◽  
Electron Spin ◽  
Spin Dynamics ◽  
Intersystem Crossing ◽  
Photophysical Processes ◽  
Electron Spin Dynamics

Electron spin dynamics are crucial to photochemical and photophysical processes. However, to large extent it is neglected in routine photochemistry studies. Herein we summarized the recent development of the electron...

scholarly journals Molecular Design Realizing Very Fast Reverse Intersystem Crossing in Purely Organic Emitter

2019 ◽  
Author(s):  
yoshimasa wada ◽  
Hiromichi Nakagawa ◽  
Soma Matsumoto ◽  
Yasuaki Wakisaka ◽  
Hironori Kaji
Keyword(s):  
Energy Gap ◽  
Molecular Design ◽  
Delayed Fluorescence ◽  
Intersystem Crossing ◽  
Triplet States ◽  
Thermally Activated Delayed Fluorescence ◽  
Light Emitting ◽  
Thermally Activated ◽  
Donor And Acceptor ◽  
Spin Inversion

Reverse intersystem crossing (RISC), originally considered forbidden in purely organic materials, has been recently enabled by minimizing the energy gap between the lowest singlet excited state (S<sub>1</sub>) and lowest triplet state (T<sub>1</sub>) in thermally activated delayed fluorescence (TADF) systems. However, direct spin-inversion between S<sub>1</sub> and T<sub>1</sub> is still inefficient when both states are of the same charge transfer (CT) nature (i.e. <sup>1</sup>CT and <sup>3</sup>CT, respectively). Intervention of locally excited triplet states (<sup>3</sup>LE) between <sup>1</sup>CT and <sup>3</sup>CT is expected to trigger fast spin-flip. Here, we report on the systematic-design of the ideal TADF molecules with near-degenerate <sup>1</sup>CT, <sup>3</sup>CT and <sup>3</sup>LE states by controlling the through-space distance between the donor and acceptor segments in a molecule with tilted intersegment angles. The new system realizes very fast RISC with a rate constant (<i>k</i><sub>RISC</sub>) of 1.2×10<sup>7</sup> s<sup>−1</sup>. The large <i>k</i><sub>RISC</sub> of the emitter resulted in great device performance in the applications to blue TADF assisted fluorescence organic light-emitting diodes (OLEDs) as well as TADF-emitter OLEDs.<br>

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