Radiationless Deactivation
Radiationless Deactivation - Related Videos
01:25
Deactivation Processes: Jablonski Diagram
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2024
Luminescence, the emission of light by a substance that has absorbed energy, is a process that involves the interaction of molecules with light. The energy-level diagram, or Jablonski diagram, is a graphical representation of these interactions, illustrating the various states and transitions a molecule can undergo. In a typical Jablonski diagram, the lowest horizontal line represents the ground-state energy of the molecule, which is usually a singlet state. This state represents the energies...
09:43
Reversible Cooling-induced Deactivations to Study Cortical Contributions to Obstacle Memory in the Walking Cat
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Cited by 3 •
2017
Complex locomotion in naturalistic environments requiring careful coordination of the limbs involves regions of the parietal cortex. The following protocol describes the use of reversible cooling-induced deactivation to demonstrate the role of parietal area 5 in memory-guided obstacle avoidance in the walking cat.
01:24
ortho–para-Directing Deactivators: Halogens
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2023
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
01:13
meta-Directing Deactivators: –NO2, –CN, –CHO, –CO2R, –COR, –CO2H
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2023
All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for the...
10:43
Developing Neuroimaging Phenotypes of the Default Mode Network in PTSD: Integrating the Resting State, Working Memory, and Structural Connectivity
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Cited by 12 •
2014
This protocol describes the complementary neuroimaging techniques of resting state structural connectivity, task-induced deactivation, and structural connectivity analyses to examine the default network in post-traumatic stress disorder. The use of synergistic methods could potentially lead to improved diagnostics and assessments of severity, outcome, and other relevant clinical factors.
FAQs
Internal conversion redistributes an excited molecule’s electronic energy into molecular vibrations while remaining within the relevant electronic-state framework. Intersystem crossing instead transfers the molecule between electronic states before the energy is dissipated. Distinguishing these routes helps chemists connect molecular energy flow with observed excited-state behavior and competing emission or photochemical pathways.
Collisions provide an environmental pathway for dissipating electronic excitation energy. During encounters with surrounding molecules, excitation can be converted into molecular motion rather than released as light. Consequently, the surrounding chemical environment can influence how rapidly an excited state loses energy and can alter the balance between radiationless processes, emission, and photochemical reaction pathways.
Radiationless deactivation competes with fluorescence, phosphorescence, and photochemical reactions for the available excitation energy. When this pathway becomes more influential, excited states can persist for different lengths of time, while the quantum yield, meaning the efficiency of a resulting process, can change. These effects provide important clues about energy flow in molecular systems.
The competition determines whether absorbed energy appears as fluorescence or phosphorescence, is converted into molecular vibrations, or remains available for a photochemical reaction. This balance shapes the observed response of a molecule to light. Studying it therefore helps explain why related molecular systems can show different emission behavior or photochemical outcomes.
Chemists compare spectral behavior with the effects expected from competing energy-loss pathways. Radiationless deactivation helps explain why excitation does not necessarily produce proportional fluorescence or phosphorescence, because some energy follows nonemissive routes. Interpreting these relationships supports analysis of how molecules redistribute electronic energy after absorbing light and helps identify relevant excited-state processes.
Controlling radiationless deactivation allows chemists to manage how molecular systems handle absorbed light. In fluorescent probes, it affects emission behavior; in photosensitizers, it influences the fate of excited-state energy; and in molecular materials, it helps regulate energy flow. The same principles also apply to light-driven chemical systems and their reaction pathways.