Quantum yield chemosensors

The dihydroxyaniline-squaraine chromophore was used by Akkaya and Isgor in the fluorescent chemosensor 30 for the measurement of pH [90]. This chemosensor, having the molar absorptivity about 200,000 M em 1 and quantum yield 0.2,... 

The possibility of measurement of Mg2+ concentration in a matrix complicated by alkali and alkaline earth metal ions has been explored by titration of 68 (5 x 10-5 M) in 1 1 MeOH/H20 solution (pH 7.2) containing Na+ (5 x 10 3 M), K+ (1 X 10-3 M), Ba2+ (1 x 10 3 M), Sr2 (1 x 1(T3 M), and Ca2+ (1 x 10-4 M). The titration was monitored via fluorescence.125 The fluorescence intensity reached a maximum at 1 equiv of Mg2+, indicating that fluorescent intensity could be directly correlated to Mg2+ concentration. The lack of interference from the other metal ions present can be a result of their lower binding constants with 68 and lower quantum yields of the charged complexes of 68 with Na+, K+, Ca2+, Sr2+, and Ba2+ at this pH. Thus, ligand 68 possesses characteristics of an efficient fluorescent chemosensor for Mg2+ and may find use in determining Mg2+ in biological samples and, if immobilized on a solid support, may be incorporated into sensory devices for measurement of Mg2+ concentrations in aqueous solutions. 

Chemosensor A molecular or supramolecular entity responding to analytes, usually following a molecular recognition event, by changes in photophysical parameters (absorbance/emission wavelength/intensity, extinction coefficient, emission lifetime, quantum yield). 

Quantum dots (QDs) have been a research focus in recent years owing to their unique optical properties, such as high quantum yields, narrow and tunable emission spectra, strong fluorescence emission intensity, long fluorescence time, and reduced susceptibility to photobleaching. The fluorescence efficiency of QDs is sensitive to the presence and nature of adsorbates on their surfaces. The introduction of an organic ligand on QD surface affords not only the stability of these nanoentities in different solvents but also the desired surface functionality, which enables them to be used as chemosensors [64]. 

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