Related Experiment Video
Updated: May 24, 2025
08:04
Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
8.3K
Excited-State Dynamics and Electron-Withdrawing Group Effects in Two-Photon Switchable Donor-Acceptor Stenhouse
Mariana M Reza1,2, Francisco A Reza-González1, Melissa Bravo-Romero1
1Instituto de Química, Universidad Nacional Autónoma de México, Ciudad de México, México.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 3, 2025
Summary
Donor-acceptor Stenhouse adducts (DASAs) exhibit two-photon switching. This study reveals higher singlet states drive the non-linear excitation and switching dynamics in DASAs, enhancing their photo-switching capabilities.
Area of Science:
- Non-linear optics
- Photochemistry
- Materials Science
Background:
- Non-linear optical reactive systems are crucial for localized effects.
- Donor-acceptor Stenhouse adducts (DASAs) were recently identified as having two-photon switching properties.
Purpose of the Study:
- To elucidate the non-linear excitation mechanism and dynamics of DASAs.
- To investigate the role of higher singlet states in two-photon switching.
- To synthesize and evaluate new DASAs with enhanced two-photon properties.
Main Methods:
- Femtosecond-resolved spectroscopic measurements.
- Synthesis of novel donor-acceptor Stenhouse adducts with varied electron-accepting groups.
- Computational modeling of electronic states and transitions.
Main Results:
- Direct evidence for the involvement of higher singlet states (Sn, n>1) in the initial two-photon absorption.
- Observation of rapid emission from Sn states followed by internal conversion to S1, leading to switching.
- New DASAs exhibit up to three times larger two-photon cross sections compared to previous compounds.
- Computational results support the role of higher singlets around 3 eV above the ground state.
Conclusions:
- Specific higher singlet states are central to the non-linear photo-switching mechanism of DASAs.
- The findings identify key molecular design variables for optimizing non-linear photo-switching in DASAs.
- Enhanced two-photon cross sections were achieved through molecular engineering.
Related Concept Videos
01:26Photochemical Electrocyclic Reactions: Stereochemistry
1.8K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
1.8K
02:26SN2 Reaction: Transition State
9.4K
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
9.4K
01:10Radical Reactivity: Steric Effects
1.9K
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
Along with electronic...
1.9K
01:25Deactivation Processes: Jablonski Diagram
551
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...
551
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
2.0K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.0K
02:23SN2 Reaction: Stereochemistry
9.1K
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not...
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not...
9.1K