abstract |
Disclosed herein are compounds or salts and/or solvates of formula I, II and III, where the compounds or salts and/or solvates have the following structures: (X) a —Y—(Z) b I; II; or X′—Y′ III; where X, Y, Z, Y′, a, b, R 4 , R 6 and R 7 are as defined herein. |