Abstract: Disclosed herein are compounds of Formula (I), or a pharmaceutically acceptable salt, ester, amide, thereof; and methods of modulating the activity of a cannabinoid CB2 receptor comprising contacting a compound of Formula I with the cannabinoid CB2 receptor. Also disclosed are methods of imaging of a tissue by positron emission tomography, the method comprising administering to the subject a compound of Formula I, wherein the compound comprises a radioisotope. Also disclosed are methods of measuring the relative concentration of cannabinoid CB2 receptors in tissue of a subject, by using a compound of Formula I which comprises a radioisotope. In addition, method of diagnosing a disorder in a subject are disclosed.