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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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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.
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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.
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Magnetic forces on wires carrying current are most frequently applied in motors. A DC motor is a device that converts electrical energy into mechanical work. In motors, wire loops are enclosed in a magnetic field. When current flows through the loops, the magnetic field applies torque, which causes the shaft to rotate. The direction of the current is reversed once the loop's surface area is lined up with the magnetic field, causing a constant torque on the loop. During the process,...
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Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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Light-Triggered Reversible Helicity Switching of a Rotor by a Photo-Responsive Plier.

Diptiprava Sahoo1, Anshuman Bera1, Sivaranjana Reddy Vennapusa1

  • 1School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Thiruvananthapuram, 695551, India.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 7, 2025
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Summary
This summary is machine-generated.

This study demonstrates a light-activated molecular plier that changes shape to control a rotor

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Area of Science:

  • Molecular mechanics
  • Supramolecular chemistry
  • Photochemistry

Background:

  • Controlling molecular motion and its transmission is challenging.
  • Remote control of molecular conformational changes requires sophisticated mechanisms.

Purpose of the Study:

  • To demonstrate a light-triggered molecular plier for reversible conformational and helical chirality control.
  • To investigate the transmission of molecular motion from a host to a guest molecule.

Main Methods:

  • Utilized an azobenzene unit for light-activated isomerization (E to Z).
  • Employed a BINOL unit as a hinge and chiral inducer.
  • Incorporated pyridine moieties for host-guest complexation with a rotor.
  • Characterized conformational changes using 1H NMR, UV-Vis, and Circular Dichroism (CD) spectroscopy.
  • Confirmed rotor response via thermal back isomerization studies and molecular modeling.

Main Results:

  • Demonstrated light-induced, scissor-like conformational changes in the molecular plier.
  • Showcased reversible alteration of the rotor's conformation and helical chirality.
  • Confirmed a 1:1 host-guest complex formation enabling motion transmission.
  • Observed light-triggered mechanical twisting and helicity switching in the rotor.

Conclusions:

  • Successfully developed a light-responsive molecular plier for controlled molecular motion.
  • Established a method for transmitting light-induced mechanical changes to a guest molecule.
  • The system offers potential for developing advanced molecular machines and sensors.