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Abstract
Catalyst-free strain-promoted alkyne-azide cycloaddition (SPAAC) has become an increasingly popular ligation strategy in the areas of material functionalization, immobilization, nano medicine, and labeling of various biological substrates. We have developed a new Oxa-dibenzocyclooctyne (ODIBO) that displays exceptional reaction kinetics with azides. ODIBO can be readily prepared by the photochemical decarbonylation of corresponding cyclopropenones (photo-ODIBO). Not only is ODIBO one of the most reactive cyclooctynes reported so far, but it also shows dramatic increase in the rate of cycloaddition in neutral aqueous solutions. We have done extensive studies comparing ODIBO to the most commonly used cyclooctynes in the literature DIBO, ADIBO, and BCN. Rate constants for all cyclooctynes in various conditions were determined as well as the stabilities of each cyclooctyne to hydrolysis, pH, and glutathione. These properties are vital for being able to choose the correct cyclooctyne for a specific application. We then applied a variety of different photo-caged cyclooctynes and cyclooctynes for application in the field of surface functionalization, nano-medicine, and drug delivery.