TECHNOLOGY FOCUS - POLYMERS - Preferred Polymer: The structural units are of formula (I)A = Si, Ge, Sn or Pb;Y = divalent aromatic or heteroaromatic ring of 1-40C substituted with one or more groups R4, vinylene group -CR4=CR4- or acetylenic group -Ctriple bondC-;X = divalent group -(Y)p- or monovalent group R3;R1-R3 = H, F, CN, N(R4)2, straight, branched or cyclic alkyl, alkoxy or thioalkoxy of 1-40C (optionally substituted with group R4, where one or more non-neighbouring -CH2- groups are replaced by -CR5C=CR5-, -Ctriple bondC-, Si(R5)2, Ge(R5)2, Sn(R5)2, C=O, C=S, C=Se, C=NR5, -O-, -S-, -NR5- or -CONR5- and one or more H atoms can be replaced by F, Cl, Br, I, CN, OH or NO2) or aromatic or heteroaromatic ring or aryloxy or heteroaryloxy group having 2-40 aromatic C optionally substituted with one or more groups R4 and where two or more or R1, R2 and/or R3 can form other mono or polycyclic, aliphatic or aromatic rings;R4 = H, F, Cl, Br, I, CN, NO2, straight, branched or cyclic alkyl or alkoxy of 1-22C (where one or more non-neighbouring C atoms are replaced by -CR5C=CR5-, -Ctriple bondC-, Si(R5)2, Ge(R5)2, Sn(R5)2, -NR5, -O-, -S-, -COO- or -OCOO- and one or more H atoms can be replaced by F, Cl, Br, I, CN or NO2), aryl, heteroaryl or aryloxy of 1-40C optionally substituted by one or more groups R5 or OH, N(R5)2, B(R5)2 or Si(R5)3;R5 = H or aliphatic or aromatic group of 1-20C,n = 1-4; andp = 1-3.Preferred Iridium complex: The iridium complex is of formula (II)DCy = cyclic group containing a donor atom, especially N or P, the cyclic group being bonded to the Ir atom and may have R6 substituents and groups DCy and CCy are covently bonded to each other;CCy = cyclic group containing a C atom, the cyclic group being bonded to the Ir atom and may have R6 substituents;L = bidendate chelating ligand;R6 = H, F, Cl, Br, I, CN, straight, branched or cyclic alkyl or alkoxy of 1-40C (where one or more non-neighbouring CH2 groups are replaced by - C=NR5, CR5C=CR5-, -Ctriple bondC-, Si(R5)2, -NR5, -O-, -S-, C=O, C=S, C=Se or -CONR5 and one or more H atoms can be replaced by F, Cl, Br, I, CN or NO2) or aromatic or heteroaromatic ring of 2-40C optionally substituted with one or more non-aromatic group R6 and where the same ring and diiferent rings can form other mono or polycyclic, aliphatic or aromatic rings; andm = 1-3.