An organic photodetector comprising a photosensitive organic layer comprising an electron donor and an electron acceptor wherein the electron acceptor is a compound of formula (I): EAG-EDG-EAG  (I) wherein each EAG is an electron accepting group; and EDG is an electron-donating group of formula (II) or (III): A photosensor may comprise the organic photodetector and a light source, e.g. a near infra-red light source.