Fluorescent sensors benzene

How does the Na" " binding cause stronger fluorescence Once bound to the receptor of 1, Na" " not only retards PET processes that take the electron away from ihe crown due to electrostatics but also causes a rotation of about 60° about the aromatic C-N bond such that the nitrogen electron pair is deconjugated from the benzene ring 7T-system. Such conformational effects are known to substantially raise oxidation potentials so that PET is seriously retarded. The receptor within 1 can also be developed into an absorptiometric sensor for Na+. ... 

The Schiff bases obtained by reaction of 4-methyl-2,6-diformylphenol with l- or D-phenylglycinol 52 (Fig. 16) were foimd to interact enantioselectively with the two enantiomers of mandelic acid on account of the appearance of a fluorescent component with a longer lifetime. A job plot of the complex formation, however, revealed a 2 3 guest host stoichiometry of the complex formed, thus suggesting an oligomeric form of the type reported in Fig. 16b. The good enantioselectivity observed (Ks/K = 4 for the (R,R)-sensor) also allowed these authors to calibrate the fluorescence response vs the enantiomeric compositions of mandelic acid in benzene solutions containing 10 " M of the sensor [81]. 

Pu and coworkers described the same type of effect on the BINOL derivative containing enantiomers of the 2-amino-1,2-diphenyIethanoI unit 55 upon interaction with enantiomers of mandelic acid in benzene. By using the (S)-sensor, (5)-mandelic acid induced precipitation and formation of a highly fluorescent suspension with an enhanced fluorescence intensity of 950 times. In contrast, (/ )-mandeIic acid did not... 

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