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AAT Bioquest

What are the factors affecting fluorescence?

Posted January 25, 2023


Answer

The main factors affecting fluorescence include: conjugated double bonds, effects of substituents and effects of pH. In molecules with more conjugated double bonds absorb a higher quantity of light and therefore cause more intense luminescence. Substituents also have an effect on fluorescence. For example, electron-withdrawing groups like NO2, COOh group and X halides decrease or can sometimes destroy fluorescence. Electron donating groups like NH2 and OH groups on the other hand increase fluorescence. pH also plays a role in fluorescence. As an example, a neutral or alkaline solution of aniline shows fluorescence in the visible region, however, in an acidic solution will not fluoresce. 

Other factors affecting fluorescence (more specifically intensity of fluorescence) are the absorption ability of excitation photons, fluorescence saturation and fluorescence quenching, and fluorescence quantum yield. It was found that fluorescence molecules with high optical absorption and high quantum yield ensures fluorescence emission. It has been determined that fluorescence molecules with high optical absorption and quantum yield guarantee fluorescence emission intensity.  Fluorescence quenching in ultra-high-vacuum was undetectable and fluorescence intensity in the atmosphere decreased greatly. 

Also, the nature of the molecule. Molecules with pi bonds and aromatic rings exhibit the highest fluorescence intensity as compared to molecules with sigma bonds; this is due less electron density between the atoms. Electron donating groups like -OH are highly fluorescent, too. 

 

Additional resources

Factors influencing fluorescence spectra of free porphyrins

FluoroQuest™ Fluorescence Quantum Yield Determination Kit *Optimized for Bioconjugates*

Intracellular pH

RatioWorks™ BCFL, AM *Superior replacement for BCECF*

Fluorescence Spectrum Viewer