Something that has a chemical reaction will fluoresce

The fluorescein in the abdomen of fireflies fluoresces when catalyzed by a series of complex biochemical reactions.

Compounds that are capable of fluoresceing and act as dyes are called fluorophores or fluorescent dyes. Some fluorophores themselves do not emit light, but they can specifically and efficiently bind to a certain type of biological macromolecule, and emit beautiful fluorescence after binding, such as nucleic acid dyes; Some fluorophores themselves can fluoresce under certain conditions, and we need to "hang" this "beacon" on some biological macromolecules that can "guide the way" in a special way, so that this macromolecule becomes a "guiding light", which can be used to locate specific areas in biological specimens or trace, which we usually call fluorescent probes.

In addition to fluorescent dyes, there is also a class of proteins that can be excited to produce beautiful fluorescence in various colors, which are often used for protein expression tags and as a tool for tracing or quantification, such as the famous green fluorescent protein, which will be introduced in a subsequent article.

Beautiful fluorescence comes from? Take a look at the trilogy in Figure 1.

Figure 1Schematic diagram of the fluorescence excitation process. (Excerpted from Molecular Probes: The Handbook).

Stage 1: Excitation.

Excitation light sources such as incandescent lamps or lasers provide photon energy hex. After the fluorophore absorbs energy, it reaches the singlet excited state (S1')。This process distinguishes between fluorescence and chemiluminescence, since the excited state of the latter is caused by a chemical reaction.

Stage 2: Lifespan of the excited state.

The excited state has a short lifespan, typically only 1 to 10 nanoseconds. During this time, the fluorophore undergoes a conformational change and a large number of interactions with the molecular environment in which it is located. There are two important outcomes of this process:

First, s1'The energy portion is partially lost, allowing the fluorophore to reach the slightly lower energy S1 singlet excited state. Second, not all excited molecules eventually return to the ground state (S0) by fluorescence emission. Processes such as collision quenching and fluorescence resonance energy transfer (FRET) also reduce S1.

Stage 3: Fluorescence emission.

At this stage, the fluorophore releases the photon energy h em, which returns to the ground state s0. Due to energy loss, the energy of the photon decreases, and the emission wavelength is always greater than its excitation wavelength, and the difference between the two is called the Stokes shift. In fluorescence analysis, the Stokes shift phenomenon is used to separate the excitation light from the emitted light of the fluorescent substance, and only the emitted light is detected, so as to improve the sensitivity and selectivity of the detection.

Some fluorochromes have a larger Stokes shift, while some fluorochromes have a smaller Stokes shift. The larger the Stokes shift, the less overlap the excitation and emission spectra are, which is beneficial to improve its resolution.

Fluorescence, a Chinese word. Also known as "fluorescence", it refers to a photoluminescent cold luminescence phenomenon. When a normal temperature substance is irradiated by incident light of a certain wavelength (usually ultraviolet or X-ray), it absorbs light energy and enters the excited state, and immediately de-excitation and emits an exit light (usually in the visible band) longer than the wavelength of the incident light.

As soon as many fluorescent substances stop being incident with light, the luminescence disappears immediately. Exit light with this property is called fluorescence. In addition, there are some substances that can still emit light for a long time after the incident light is removed, and this phenomenon is called afterglow.

In daily life, people usually refer to all kinds of faint light as fluorescence in a broad sense, without carefully investigating and distinguishing their luminescence principles. It also refers to cold light with a low temperature (not color temperature).

parameters

1) Excitation spectrum: the relationship between the intensity or luminous efficiency of a certain emission spectrum line and the spectral band of the luminescent material and the wavelength of the excitation light under the excitation of different wavelengths of light.

2) Emission spectrum: the intensity of luminous materials of different wavelengths under the excitation of a certain excitation light.

3) Fluorescence intensity: The fluorescence intensity is related to the fluorescence quantum yield, extinction coefficient and content of the substance.

4) Fluorescence quantum yield Q: The quantum yield indicates the ability of a substance to convert the absorbed light energy into fluorescence, which is the ratio of the number of photons emitted by the fluorescent substance to the number of photons absorbed.

The above content refers to Encyclopedia - Fluorescence.

The fluorescence reaction involves placing the gemstone in a camera camera obscura, and then using long-wave ultraviolet or short-wave ultraviolet light to illuminate the gemstone.

Look at the fluorescence reaction of jewelry is a very important identification basis in the identification of jewelry, simply put, the gemstone is put into a camera obscura, and then use long-wave ultraviolet or short-wave ultraviolet light to irradiate, if the gemstone will shine when irradiated, this light is called fluorescence, in jewelry identification, because the fluorescence reaction of natural gemstones and artificially treated gemstones will be significantly different, so the fluorescence reaction of jewelry will be used to identify the authenticity.

The role that fluorescence can play in jewelry:

Natural rubies, chrysoberyls, emeralds fluoresce red under long-wave ultraviolet light, diamonds fluoresce blue-white, and yellow sapphires and colorless sapphires from Sri Lanka fluoresce apricot yellow. Of course, some man-made gemstones also fluoresce, such as artificial blue spinel, artificial red spinel and artificial rubies will also fluoresce red under long-wave ultraviolet light. Artificial green spinel, or synthetic sapphires, are capable of emitting a greenish blue light.

In jadeite, if it shows a powder-blue fluorescence reaction under the irradiation of long-wave ultraviolet light, then this jadeite is likely to be a B jadeite, and the fluorescent part is likely to be injected with resin, so this is the reason why the fluorescence effect can be used to identify the authenticity of jewelry and jade. <>

When the test object is irradiated with ultraviolet light, the object emits blue or green light, which is the fluorescence reaction brightness. It is a phenomenon that can be observed with the naked eye. Objects with fluorescent reactions have a wide visible blue light under the ultraviolet lamp of the hall acacia hall.

Fluorescent reaction does not mean that there is a fluorescent agent in it, and all substances with fluorescent reaction can be fluorescent by ultraviolet light, such as chlorophyll, vitamin A, E, green tea, chitin, etc. It is called natural fluorescence, which is an intrinsic property of the substance and is harmless.

Let's talk about the special structure of the substances that can produce fluorescence reactions, let's take a look at a few compounds.

1. Vitamin A: In daily care, many people use it as a good anti-aging ingredient. This ingredient can produce yellow-green fluorescence under ultraviolet light, and its maximum absorption wavelength is 328nm, and its chemical formula is shown in the figure below.

2. Vitamin E: The conjugated system in the chemical structure is smaller than vitamin A, and it can produce a relatively strong fluorescence reaction near ultraviolet 280nm, and the following figure shows its chemical formula.

3. What is the difference between fluorescent agents and other things that produce fluorescent reactions?

Fluorescent agent is a large class of special white dyes, which can absorb excitation light and produce obvious bright white light, so as to make the outside of the item more white and bright. Fluorescent agents can produce fluorescent reactions, but fluorescent reactions are not the only things that produce fluorescent reactions.