A composition comprising a first material substituted with at least one group of formula (I) and a second material substituted with at least one group selected from groups of formulae (IIa) and (IIb): wherein: Sp1 and Sp2 are spacer groups; NB independently in each occurrence is a norbornene group that may be unsubstituted or substituted with one or more substituents; n1 and n2 are 0 or 1; m1 is 1 if n1 is 0 and m1 is at least 1 if n1 is 1; m2 is 1 if n2 is 0 and m2 is at least 1 if n2 is 1; Ar1 represents an aryl or heteroaryl group; R1 independently in each occurrence is H or a substituent; and * represents a point of attachment to the first or second material. The composition may be used to form a layer of an organic electronic device, for example the hole-transporting layer of an organic light-emitting device.