Synthesis and Photoisomerization Reactions of Norbornadienes Possessing Chalcone Chromophore and Reactions of the Formed Quadricyclane Derivatives

Abstract

Norbornadiene-quadricyclane photo-thermal isomerization system is one of the most important and popular solar energy storage system. However, norbornadiene -itself does not possess any absorption band in visible light region where the solar light energy is the most denseregion.
For efficient utilization of solar light energy, norbornadienes [1] which possess a chalcone chromophore were synthesized by Diels-Alder reaction of cyclopentadiene with dehydrochalcones. Photoisomerization reactions of [1] gave corresponding quadricyclane derivatives [2] in good yields. The quantum yields of the isomerizations are O.06-0.60. The properties of [1] and [2] and the results of the reactions are shown in Table 1. Solvent effects and wavelength dependency of the isomerizations are also presented.
Isomerizations of [2] to [1] were carried out by contact with silver perchlorate, with trifluoroacetic acid, and even with silica gel. All the isomerizations proceeded under very mild conditions.