Effect of Binding and Conformation on Fluorescence Quenching in New 2‘,7‘-Dichlorofluorescein Derivatives. TYPES OF QUENCHING Concentration quenching: At low concentration linearity is observed. A second type of quenching mechanism, termed static or complex quenching, arises from non-fluorescent complexes formed between the quencher and fluorophore that serve to limit absorption by reducing the population of active, excitable molecules. Static and Dynamic Quenching: Two types of quenching mechanisms are commonly found. Fluorescence Quenching and Fluorescence Resonance Energy Transfer. Fig: Quenching of quinine fluorescence in presence of chloride ions This is a trivial type of quenching which contains little molecular information. This type of complex is called static quenching and it can be described with the following equations: As said in the section on the Stokes shift, fluorescence is a very sensitive method for studying the local environment around the fluorophore. Fluorescence quenching is a physicochemical process that lowers the intensity of emitted light from fluorescent molecules. Quenching of fluorescence Quenching refers to any process that reduces the fluorescence intensity of a given substance. For example, high optical densities or turbidity can result in decreased fluorescence intensities. Methods of fluorescent quenching include fluorescence resonance energy transfer (FRET), collision quenching and contact quenching, which are diagrammed below. 4 Dynamic quenching is described by the Stern-Volmer mechanism and results by collisions of the excited state molecule with the quencher. This may occur due to various factors like pH, concentration, temperature, viscosity, presence of oxygen, heavy metals or, specific chemical substances etc. When this complex absorbs light, it immediately returns to the fundamental state without emitting any photons. Fluorescence quenching can also take place by the formation at the ground state of a non-fluorescent complex. Rational design of novel photoinduced electron transfer type fluorescent probes for sodium cation. 2 3. The order of quenching efficiency is G