The present invention provides a compound represented by the following formula (I), a pharmaceutically acceptable salt thereof, or a solvate thereof.wherein:R1 and R2 are each separately selected from the group consisting of hydrogen, alkyl, alkenyl, acyl, and hydroxyalkyl；R3 is hydrogen or halogen；ring A is a benzene ring or a pyridine ring；ring B is selected from the group consisting of the following formulas (i), (ii), (iii), and (iv):in the formula (ii), Ra is alkyl；R4 and R5 are each separately selected from the group consisting of hydrogen, hydroxy, alkoxy, haloalkoxy, halohydroxyalkoxy, and aminoalkyl； and[Formula 3]represents a double bond or a triple bond. The above compound can be used as a molecular probe for imaging tau proteins that accumulate in the brain.
