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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.
Selection Rules: Photochemical Activation
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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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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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.0K
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.
2.0K
P-N junction01:11

P-N junction

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A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by the...
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Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

3.1K
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...
3.1K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.1K
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.
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Updated: Jun 27, 2025

Morphology Control for Fully Printable Organic–Inorganic Bulk-heterojunction Solar Cells Based on a Ti-alkoxide and Semiconducting Polymer
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Conjugated Polymer Heteroatom Engineering Enables High Detectivity Symmetric Ambipolar Phototransistors.

Davide Nodari1, Sandeep Sharma2, Weitao Jia1

  • 1Department of Chemistry & Centre for Processable Electronics, Imperial College London, London, W12 0BZ, UK.

Advanced Materials (Deerfield Beach, Fla.)
|April 29, 2024
PubMed
Summary

Researchers engineered organic phototransistors (OPTs) using a novel polymer, enhancing charge transport for low-cost electronics. This breakthrough improves ambipolar performance for near-infrared (NIR) detection and photo-inverters.

Keywords:
NIR‐detectionambipolar invertersambipolar organic transistorsorganic phototransistorssolution‐processed

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Area of Science:

  • Organic electronics
  • Materials science
  • Semiconductor physics

Background:

  • Solution-processed organic phototransistors (OPTs) are crucial for developing low-cost integrated circuits.
  • Achieving balanced charge transport and high performance in OPTs remains a key challenge.
  • Heteroatom engineering offers a pathway to tune polymer properties for improved device characteristics.

Purpose of the Study:

  • To demonstrate a heteroatom engineering approach for modifying a low band gap diketopyrrolopyrrole (DPP) co-polymer.
  • To enhance electron affinity, charge transport balance, crystallinity, and orientation in organic semiconductors.
  • To investigate the application of the engineered material in high-performing ambipolar OPTs for NIR detection and photo-inverters.

Main Methods:

  • Synthesized a novel DPP co-polymer (PDPP-BO) by replacing sulfur with oxygen in the benzothiadiazole (BT) comonomer, forming benzooxadiazole (BO).
  • Fabricated organic thin film transistors (OTFTs) using the PDPP-BO material.
  • Characterized the electronic and optoelectronic properties of the fabricated devices, including charge carrier mobility, photoresponsivity, and detectivity.

Main Results:

  • The substitution of sulfur with oxygen in the DPP co-polymer significantly increased electron affinity and ambipolarity.
  • PDPP-BO based OTFTs exhibited high charge carrier mobilities of 0.6 cm²Vs⁻¹ for electrons and 0.3 cm²Vs⁻¹ for holes.
  • Ambipolar OPTs demonstrated excellent NIR detection capabilities with high photoresponsivity (69-99 A/W) and specific detectivity (up to 4 × 10⁹ Jones), alongside a high on/off ratio (9 × 10⁴).
  • The devices functioned as ambipolar photo-inverters with a 46% gain enhancement under illumination.

Conclusions:

  • Heteroatom engineering by incorporating oxygen into DPP co-polymers is an effective strategy for achieving well-balanced charge transport and high performance in organic electronics.
  • The novel PDPP-BO material enables high-performance ambipolar organic phototransistors suitable for sensitive NIR detection and advanced applications like photo-inverters.
  • These findings pave the way for developing low-cost, solution-processed ambipolar organic electronic circuits.