Iodine can be considered as the simplest halogenbond donor. Previous investigations have revealed its remarkable catalytic effect in various reactions. The catalytic activity of iodine can often even compete with that of traditional Lewis acids. So far, iodine was typically used to activate carbonyl derivatives like Michael acceptors. We now demonstrate that iodine can also be used to activate allyl aryl ethers in Claisen rearrangements. The formed ortho-allylic phenols rapidly undergo iodocyclizations to afford dihydrobenzofurans, which are important building blocks for medicinal applications. A comparison with different catalysts further highlights the potential of iodine catalysis for this reaction. Computational and mechanistic investigations provide deeper insights into the underlying non-covalent interactions and their role for the catalysis.

Achieving synthetic control over light-driven molecular dynamics is essential for designing complex molecule-based devices. Here we design a novel coumarin-imidazole conjugate (1) whose excited state structural dynamics are primarily controlled by a distant intramolecular H-bonding interaction within the backbone. The coumarin conjugate is based on a 1,2,4,5-aryl substituted imidazole framework (aryl = -Ph and -PhOH) covalently connected to the coumarin moiety via a C-N bond. A carefully positioned OH group in the aryl part of the imidazole fragment resulted in achieving two dissimilar O-HN and O-HO distal intramolecular hydrogen bonding interactions. NMR studies in conjunction with density functional theory (DFT) at the B3LYP/6-311G(d,p) level of theory show the existence of two ground state conformers with a rotational barrier of 6.12 kcal mol. Due to the presence of conformational isomers of 1, the local excited state dynamics of the parent coumarin get biased towards a long-lived fluorescence state with diminished non-radiative decay channels. Time-resolved emission studies show an ∼4-5 times increase in the excited state lifetime in 1 when compared to coumarin-imidazole conjugates, 2 and 3, without the OH group. Solvent dependent studies show that solvent polarity, the H-bond donating ability and viscosity dictate the conformational distribution in the ground state and the dynamical evolution to the final emissive state. Our studies highlight the importance of rotamerism around the C1-C4 single bond, which leads to rigidification along the coumarin-imidazole backbone through a combination of distal H-bonding and solvent interactions. The concept of new emission signaling pathways caused by conformational switching between two states offers a new paradigm to introduce functional allostery in macromolecular backbones.