Environmental factors affecting fluorescence

Rhodamine differs from malachite green in the same way as fluorescein differs from phenolphthalein. The latter is known to be non-fluorescent. 

The photophysics of fluorophores undergoing photoinduced charge transfer and/or internal rotation(s) is often complex. Time-resolved fluorescence experiments, transient absorption spectroscopy measurements, quantum chemical calculations, and comparison with model molecules are helpful in understanding their complex photophysical behavior. 

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The above show that both the quantum yield and fluorescence lifetime can be modified by any factor that affects the relative contributions of the nonradiative (k) and radiative (F) decay processes. As described in Section 2.2, these factors include environmental factors such as solvent polarity, ionization and... 

Fluorescence is generally more sensitive to environmental factors than absorbance measurements. Signal intensity may be affected by pH, temperature, quenching, interfering substances, solvent, or interference from Rayleigh and Raman scattering. Many fluorescent species contain ionisable groups whose fluorescent properties are sensitive to pH. In some cases only one of the ionised species may be fluorescent. An example is the barbiturates which only fluoresce at elevated pH in the di-anionic form. The relationship of fluorescence intensity with pH should always be examined as part of the development of the method. 

Temperature is one of major environmental factors that affects plant growth. Heat stress could completely inhibit photosynthesis before other stress symptoms are detected.1 Delayed fluorescence (DF), emitted from chloroplasts, has been demonstrated to be a sensitive indicator of photosynthetic efficiencies and stress factors.2 9... 

Fluorescence is an extremely sensitive technique but it is not suitable as a general method to estimate natural DOC content due to the reason that it is impossible to find a reference material that would be common for all different natural waters. Characteristic for different fluorescence studies of NOM/DOM is that they may occasionally be somewhat surprising, contradictory, or laboriously explicable. The main reason for this incoherence is that fluorescence measurements are affected by many environmental factors, e.g., type of solution, pH, ionic strength, temperature, redox potential of the medium, and interactions with metal ions and organics. Several corrections are required to obtain a reliable and comparable spectrum, e.g., instrumental factors, Raman water peak, scattering effects (primary and secondary inner filter effects [31,32]), arbitrary fluorescence units should be standardized (dihydrate of quinine sulfate), etc. 

The improved brightness should also be discussed in terms of the extent of quenching of the fluorophore by environmental factors. Among Aequorea GFP variants, YFPs are relatively acid sensitive, and uniquely quenched by halide ions, including chloride (CT). Proton (H+) and Cl synergisticaUy affect the charge state of the chromophore of YFP, thereby suppressing its fluorescence. Citrine and Venus show increased resistance to both and Cl [7,8]. 

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