Modulation of Protolytic Equilibrium of Bichromophoric Coumarin-30 Dye with Cucurbit[8]uril Encapsulation

Internal Dynamics and Modular Peripheral Binding in Stimuli-Responsive 3 : 2 Host:Guest Complexes

Now that the chemistry of 1 : 1 host:guest complexes is well-established, it is surprising to note that higher stoichiometry (oligomeric) complexes, especially those with excess host, remain largely unexplored. Yet, proteins tend to oligomerize, affording new functions for cell machinery. Here, we show that cucurbit[n]uril (CB[n]) macrocycles combined with symmetric, linear di-viologens form unusual 3 : 2 host:guest complexes exhibiting remarkable dynamic properties, host self-sorting, and external ring-translocation. These results highlight the structural tunability of cucurbit[8]uril (CB[8]) based 3 : 2 host:guest complexes in water and their responsiveness toward several stimuli (chemicals, pH, redox).

One-Pot Synthesis of 4-Carboalkoxy-Substituted Benzo[h]coumarins from α- and β-Naphthols and Their Excited-State Properties

One-pot synthesis has been developed for 4-carboethoxybenzo[h]coumarins starting from α-/β-naphthols. Accordingly, diverse 4-carboethoxybenzocoumarins can be synthesized in moderate-to-excellent (31-75%) isolated yields. The synthesis involves initial oxidation of naphthols to the intermediary 1,2-naphthoquinones with 2-iodoxybenzoic acid followed by a cascade of reactions, namely, Wittig olefination, Michael addition, β-elimination, and cyclization. Furthermore, we have comprehensively investigated the excited-state properties of differently substituted 4-carboalkoxybenzo[h]coumarins. It is shown that they exhibit low to high fluorescence quantum yields (1-36%) and excited-state lifetimes (ca. 1-7 ns) depending on the substitution pattern and solvent employed.