wherein X is OH, C1-C6 alkoxyl Y and Z are independently selected from a C1-C6 alkyl, C1-C6 alkoxyl, halogen, mi-substituted or C1-C6 substituted amine, 18F, 19F, or H and n is 1, 2, or 3 and wherein for structure (I), if n are both 1 and Y and Z are both H and X is OH.