PHOTOACTIVE MATERIAL

A material comprising an electron-accepting unit of formula (I). According to some embodiments, the present disclosure provides a material comprising an electron-accepting unit of formula (I) wherein Ar is a substituted or unsubstituted benzene or 6-membered heteroaromatic ring containing N and C ring atoms; Ar1 is a substituted or unsubstituted 5- or 6-membered heteroaromatic ring containing N and C ring atoms; Ar2 is a substituted or unsubstituted 5- or 6-membered heteroaromatic ring or is absent; Ar3 is a 5-membered ring or a substituted or unsubstituted 6-membered ring; Ar4 is a 5-membered ring or a substituted or unsubstituted 6-membered ring or is absent; Ar5 is a substituted or unsubstituted monocyclic or polycyclic group containing at least one aromatic or heteroaromatic ring; Ar6 is a substituted or unsubstituted monocyclic or polycyclic group containing at least one aromatic or heteroaromatic ring or is absent; and each X is independently a substituent bound to a carbon atom of Ar3 and, where present, Ar4 with the proviso that at least one X group is an electron-withdrawing group and wherein the material further comprises a conjugated electron-donating unit. The material may be a polymer comprising repeat units of formula (I). The material may be a non-polymeric compound. An organic photodetector may contain a bulk heterojunction layer containing an electron acceptor or an electron donor wherein at least one of the electron acceptor and electron donor contains a unit of formula (I).