The binding of guest molecules sensitively influences the fluorescent behaviour of barbiturate-incorporated fluorescent pyrenes, making it possible to 'read-out' the molecular-recognition process by a fluorescence spectroscopic technique.

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A fluorescent receptor, N,N′-bis[6-[4-(1-pyrenyl)butanamido]-2-pyridyl]isophthalamide (2), was synthesized to develop a sensitive host–guest-type sensory system for barbiturates. 2 aggregates in cyclohexane and the pyrene fluorescence in 2 almost disappeared because of aggregation-induced concentration quenching. The addition of barbital to the cyclohexane solution of 2, which induced the deaggregation of 2 through complementary complexation with barbital, increased the fluorescence intensity at 378 nm by a factor of about 70-fold. The barbiturates in water could also be sensitively detected by 2 based on a liquid (water)–liquid (cyclohexane) extraction technique. In this system, 2 was essentially selective for barbiturates and no fluorescence response was observed for guests including a hydantoin skeleton. The analogue of 2, which has the N,N′-di-(2-pyridyl) terephthalamide skeleton, was also investigated as a fluorescent receptor for dicarboxylic acids.

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