The Chemistry of fluroscence
Sreelakshmi P Vijayan
Fluorescence is the ability of certain chemicals to release visible light after absorbing an invisible radiation, such as ultraviolet light. It is a form of luminescence where molecules on absorbing light energy excites to a higher energy state, also known an excited state. Since the energy of the excited state is too high the molecule cannot sustain there for long time and it comes to lower energy level by emission of light energy. This emitted light has longer wavelength and hence have lower photon energy than the absorbed radiation.
This process of fluorescence occurs when the absorbed radiation is in the UV region of the electromagnetic spectrum which is undetectable to the human eye, and the emitted radiation is in the visible region. That’s why a fluorescent material exhibits a very distinctive color and it can only be viewed when exposed to UV light.
In energy efficient fluorescent and LED lamps, where fluorescent coatings convert UV (blue light) into longer-wavelengths resulting in white light is a most common application of fluorescence. It also has many practical applications including in medicinal field, production of biological detectors, chemical sensors, fluorescent dyes, fluorescent labelling etc.
Bio fluorescence- fluorescence exhibited by bio- organisms in nature is termed as bio-fluorescence. Fluorescence is a passive physical property whereas bioluminescence is a property that animals cannot actively turn on and off. The Pumpkin toadlets and Flower Hat Jellyfish in the Brazilian Atlantic forest exhibits bio-fluorescence. The flower hat jellies use their fluorescent tentacles as baits to attract prey as they prey gets misguided that it might be some fluorescent algae, since the chlorophyll in algae is also naturally fluorescent.
Under UV light, different substances exhibiting fluorescence are known as fluorophore. Fluorescent green is a fluorescein, yellow is Rhodamine 6G, red is Rhodamine B, blue is quinine and purple is a mixture of quinine and rhodamine 6G. This fluorescence by fluorophores are owed to delocalized electrons. Benzene (C6H6), a simplest aromatic hydrocarbon excites at 254 nm and radiates at 300 nm. They can be attached to protein to a specific functional moiety, such as amino group, ester, carboxylate, isothiocyanate, thiol, organic azide (N=N) etc.
Rainbow of Fluorescent Corals - Why do they Glow?
Deep underneath the Red Sea, scientists have discovered fluorescent corals in a range of colors. Corals generally glow due to the fluorescent pigments in them which act as sunblock. The sun’s intense rays that falls on these reefs, may damage the coral and zooxanthellae, a symbiotic algae which lives inside coral. From corals, sea turtles, sea urchins to eels, innumerable marine species are bio fluorescent, that they have the ability to reflect the blue light hitting a surface and transform it and then re-emit it as a different color. It is common phenomenon among marine fish species, specifying its potentiality in communication and mating. This opens the door for the discovery of novel fluorescent proteins that might be used in biomedical investigation and research. These pigments possibly will help the scientists to tag certain types of cells, assisting surgeons to view cancer cells in the body.
“The more colors, the merrier.”
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Check your knowledge
Fluorescence is a form of luminescence, where certain substances release low energy visible light after absorbing an invisible radiation.
It occurs when a molecule travels from a region of excited state (high energy level) to ground (lower energy level) state by emitting radiation in the visible region
It occurs when a molecule travels from a region of excited state (high energy level) to ground (lower energy level) state by emitting radiation in the visible region
When initial and final states have different spin multiplicity fluorescence becomes phosphorescence.
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