Related Concept Videos
01:26Photochemical Electrocyclic Reactions: Stereochemistry
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
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
02:11Conformations of Cyclohexane
Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
01:28Stability of Conjugated Dienes
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:15The Antenna Complex
Plants and other photosynthetic organisms comprise pigments capable of absorption of direct sunlight. These pigments are present in the reaction center - the main site of photochemical reactions as well as in the antenna complex. Under average light conditions, the rate at which reaction center pigments absorb light is far below the electron transport chain's capacity. As a result, the reaction center alone cannot provide enough energy to drive photosynthesis. The photosynthetic efficiency can...
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Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation
Published on: August 1, 2018
Constructing Conformation-Restricted Terpyridine Complexes by Manipulating the Flexible Chain Length for
Zhengguang Li1, Tao Zhang1, Fan Fu1
1Department of Organic and Polymer Chemistry, Hunan Key Laboratory of Micro & Nano Materials Interface Science, College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, China.
Inorganic Chemistry
|June 8, 2026
Summary
Researchers developed conformation-restricted terpyridine complexes to boost photocatalysis. Shorter flexible chains improved performance, with complex S-12 achieving a high H2O2 evolution rate, demonstrating enhanced exciton dissociation.
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Area of Science:
- Materials Science
- Photocatalysis
- Organic Chemistry
Background:
- Precise control over molecular conformation is key to enhancing photocatalytic efficiency.
- Developing strategies for conformation-restricted molecular designs is an ongoing challenge.
Purpose of the Study:
- To introduce a novel strategy for creating conformation-restricted charge-transfer (CT) complexes.
- To investigate the impact of flexible chain length on molecular conformation, electronic structure, and photocatalytic activity.
Main Methods:
- Synthesis of three terpyridine-based CT complexes (S-12, S-13, S-14) with varying flexible chain lengths.
- Comprehensive characterization of their electronic structures and excited-state properties.
- Evaluation of their photocatalytic performance, particularly for H2O2 evolution.
Main Results:
- Conformation restriction was successfully tuned by manipulating flexible chain length.
- Complex S-12, with the shortest chains, exhibited the most restricted conformation, longest excited-state lifetime, and stabilized CT excited state.
- Photocatalytic performance increased progressively from S-14 to S-12 due to enhanced exciton dissociation.
Conclusions:
- Restricted molecular conformation significantly improves photocatalytic performance by stabilizing charge-transfer excited states.
- Complex S-12 demonstrated exceptional H2O2 evolution (7905 μmol g-1 h-1) in pure water under air, outperforming many organic photocatalysts.
- This work provides a valuable example of optimizing photocatalysis through conformational control.