Abstract: A compound of Formula I, Formula II, Formula III, Formula IV, Formula V, or Formula VI, or a pharmaceutically acceptable salt thereof. The structure of Formula I is: wherein R1 is a halogen; n is 0, 1, or 2; X1, X2, X3, X4, X5 and X6 are each independently C or N; R2 is absent or O; and R3 is absent or —CN.

Abstract: High quantum efficiency (.gtoreq.5%) ultrafast (.ltoreq.100 picosecond) and broad band (30 KeV to 80 KeV for medical application) X-ray photo-electron cathode, high gain X-ray real time image intensifier and portable low intensity real time projection type X-ray imagescope use new vacuum photo-electron devices. A new type X-ray photo-electron cathode has a specially designed alkali halide electron emission layer that makes possible high quantum efficiency, high speed and broad band X-ray photon detection. An X-ray photo-electron cathode followed by a direct coupled micro channel plate and an output phosphor display screen form a new type panel shaped direct view X-ray intensifier tube which can have both high spatial resolution (.gtoreq.10 lp/mm) and high gain (.gtoreq.10.sup.4). The thickness of this panel shaped disc X-ray intensifier can be less than 1 cm.