Incorporation of Benzobisoxazole Cruciforms into Metal-Organic Frameworks and the Development of Fluoride sensors Based on Benzobisoxazole Cruciforms



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Fully π-conjugated cross-shaped molecules known as molecular cruciforms have been studied for applications as versatile fluorescence sensors because they are characterized by spatially isolated frontier molecular orbitals, and thus a highly modular HOMO–LUMO gap leads to unique electronic and optical properties. In previous studies, benzobisoxazole-centered cruciform molecules with diverse substitution were developed, and these showed potential applications as chemosensory materials for numerous analytes. Based on the previous findings, solid-state sensors utilizing benzobisoxazole cruciforms which incorporated into porous crystalline materials, so called metal-organic frameworks (MOFs), through their coordination to transition metals were explored. A crystal structure of the first MOF incorporating a benzobisoxazole cruciform demonstrated the potential for rigid and strong optical solid-state materials where analytes could be transferred to the interior binding site on cruciforms through lots of pores of frameworks. An alternative synthetic method for our benzobisoxazole-bearing cruciforms was also suggested to achieve the large-scale preparation in enhanced yield. In addition, a new class of silyl alkyne cruciform which acts as sensitive and selective sensors for fluoride has been developed. The computational and spectroscopic studies revealed that these silylated benzobisoxazole cruciforms responded specifically to fluoride resulted from the desilylation of silylated alkynes while other anions did not make any chemical and optical changes.



Metal-organic frameworks, Conjugation, Cruciform molecules, Fluoride sensor