Synthesis of spiropyrans as building blocks for molecular switches and dyads.

The synthesis of spiropyrans was improved significantly with use of ultrasonic radiation. To show the broad applicability of this methodology a range of spiropyrans were prepared which are equipped with iodo, hydroxyl, ethinyl, or azido groups as potential building blocks for conjugation to functional pi-systems or biopolymers. Representatively, the conjugation chemistry was demonstrated for the preparation of spiropyran conjugates with pyrene, perylene, and nile red via the "click"-type cycloaddition. These molecular dyads were characterized by optical spectroscopy.