Patent ID: 8624232

Claim:
A compound of formula I: [ D a - A core - D b - A c -] n (I) wherein each A core is an electron accepting fused heteroaromatic group having at least one nitrogen atom in the backbone of the heteroaromatic group and at least one S, O or Se atom either in the backbone of the heteroaromatic group or as a conjugated substituent on the heteroaromatic group; each D is an independently selected conjugated electron donating aromatic or heteroaromatic group having from 5 to 50 backbone atoms, each D optionally substituted with one or more electron donating substituents or electron withdrawing substituents, provided that even when substituted the electronic character of each D is electron donating; each A is an independently selected conjugated electron accepting aromatic or heteroaromatic group having from 5 to 50 backbone atoms or an ethenylene group substituted with one or two electron withdrawing substituents, each A being optionally substituted with one or more electron donating substituents or electron withdrawing substituents provided that even when substituted the electronic character of each A is electron accepting; n is an integer having a value of from 2 to 10000; and each a, each b and each c is independently an integer from 1 to 4.