Turn-on fluorescence sensors based on dynamic intramolecular N -> B-coordination

• A series of ten aryl-triazole-functionalized boranes bearing BMes(2)-groups and capable of forming intramolecular five-membered N -> B-coordinated heterocycles, has been prepared by 1,3-dipolar cycloaddition. Electronically diverse substituents ranging from 4-NMe2-phenyl (4-NMe2) and 4-OMe-phenyl (4-OMe) to 4-cyanophenyl (4-CN), 4-nitrophenyl (4-NO2) and pentafluorophenyl (C6F5) have been introduced in the periphery of the compounds to systematically vary their electronic properties and the strength of the N -> B-coordination. Experimental and computational studies show that the boranes exist in dynamic equilibrium between aclosedN -> B-coordinated conformation and two types of non-coordinated conformations (open(syn)andopen(anti)). Their structural, optical and electrochemical properties have been characterized, and their binding affinities for nucleophilic anions has been tested. Individual boranes exhibit either fluorescence quenching (4-Me,4-OMe) or fluorescence turn-on (4-CN,4-CF3,C6F5,3,5-(CF3)(2)) upon coordination of anions. Further analyses show that the binding affinity to cyanide can be tailored through variation of the peripheral substituent, ranging from 5.79 (+/- 0.11) for4-Meto 6.53 (+/- 0.15) for the4-CN-substituted borane. These experimental data correlate with computed anion binding affinities, which indicate that the effective Lewis acidity at boron covers a range reaching from the parent compound PhBMes(2)to the much more Lewis acidic Ph3B.

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NATURVETENSKAP  -- Kemi -- Organisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Organic Chemistry (hsv//eng)

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