A Benzothiazinonecopillar[5]arene Derivative: Synthesis, Supramolecular Aggregation, and Fluorogenic Detection of Strong Bases, Including DBU

A new copillar[5]arene with benzothiazinone motif HBTP has been synthesized, characterized, and studied for its molecular recognition of basic analytes. This new copillar[5]arene is structurally unique and exhibits supramolecular assemblies in the solid state, involving different weak noncovalent forces. Owing to the presence of free phenolic −OH and an amide group, HBTP responds fluorometrically to basic analytes through a deprotonation mechanism. DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) is selectively screened from a series of aliphatic and aromatic amines by the macrocycle in CH 3 CN. However, some structurally related bases, such as DBN (1,5-diazabicyclo[4.3.0]non-5-ene), TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), and MTBD (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene), bring similar results in fluorescence in CH 3 CN. Under identical conditions, non-nitrogenous bases, such as F – and AcO –, show a similar response. Although HBTP responds to F –, AcO –, DBU, DBN, TBD, and MTBD in CH 3 CN by showing an emission at ∼560 nm, it is highly responsive to DBU in aqueous CH 3 CN. The detection limit for DBU is found to be 1.38 × 10 –7 M in CH 3 CN. The emission characteristics of this macrocycle toward these analytes have been observed to differ in the solid state. The paper strip prepared from HBTP also clearly distinguishes them and enables the selective detection of DBU. Apart from these, the macrocycle is redox-active and responds differently toward DBU and F – . The electronic properties of HBTP in the absence and presence of DBU have been corroborated theoretically.