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相关概念视频

Ultraviolet and Visible (UV–Vis) Spectroscopy: Overview01:02

Ultraviolet and Visible (UV–Vis) Spectroscopy: Overview

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Ultraviolet–visible (UV–visible or UV–Vis) spectroscopy is an analytical technique that investigates the interaction between matter and UV–Vis light within the electromagnetic spectrum. This method is widely used for its versatility, simplicity, and relatively quick data acquisition, making it valuable for both qualitative and quantitative analysis. When UV–Vis radiation passes through a material,  molecules absorb light depending on the energy required for...
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UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

UV–Vis Spectroscopy: Molecular Electronic Transitions

3.2K
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
3.2K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.3K
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
2.3K
UV–Vis Spectroscopy of Conjugated Systems01:32

UV–Vis Spectroscopy of Conjugated Systems

8.6K
Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent of conjugation in...
8.6K
Photoelectric Effect02:26

Photoelectric Effect

40.4K
When light of a particular wavelength strikes a metal surface, electrons are emitted. This is called the photoelectric effect. The minimum frequency of light that can cause such emission of electrons is called the threshold frequency, which is specific to the metal. Light with a frequency lower than the threshold frequency, even if it is of high intensity, cannot initiate the emission of electrons. However, when the frequency is higher than the threshold value, the number of electrons ejected...
40.4K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

3.1K
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.
3.1K

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相关实验视频

Updated: Feb 27, 2026

Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch

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圆形光物理学重新审视

Johannes Wega1, Eric Vauthey1

  • 1Department of Physical Chemistry, University of Geneva, 30 Quai Ernest-Ansermet, 1211 Geneva, Switzerland.

The journal of physical chemistry. A
|February 25, 2026
PubMed
概括

这项研究澄清了圆体光物理,揭示了它的S1 ← S0过渡是禁止的,S2 ← S0是允许的. 温度对圆体有影响.

科学领域:

  • 光物理学的光学物理学
  • 频谱学是一种光谱学.
  • 纳米摄像头的使用方法

背景情况:

  • 乙烯是一种纳米基基因,其报道的光谱学结果相互矛盾.
  • 它的D2h点群对称性使其与较大的烯分子相比较.

研究的目的:

  • 重新调查和澄清卵烯的光物理特性.
  • 解决之前对卵烯的光谱发现中的差异.
  • 建立一个可靠的模型来理解烯的兴奋状态.

主要方法:

  • 吸收和极化发射光谱学.
  • 温度依赖和时间分辨率的光谱测量.
  • 使用适用于二烯激发状态的模型进行分析.

主要成果:

  • 在烯中S1 ← S0过渡被证实是禁止的 (1B3u ← 1Ag).
  • 突出的吸收带被分配给允许的S2 ← S0过渡 (1B2u ← 1Ag).
  • 观察到S1和S2状态之间的快速热前平衡,导致热激活的S2 → S0发射.

结论:

  • 烯的光物理可以用烯激发状态模型来解释.

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Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
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  • 烯中的S2-S1能量差距大约为1200cm-1,比之前报道的要大.
  • 由于S1-S2热平衡,温度影响了烯的光寿命和量子产量.