TECHNOLOGY FOCUS - POLYMERS - Preferred Copolymers : The copolymers also contain green- emitting units (G) at 0.001-3 mol.% with the fraction of units R being less than that of units G and the ratio R : G being 1 : 50-1.1. Especially preferred copolymers contain units B at at least 20 mol., units (G) at up to 2 mol.% and units R at 0.0005-0.5 mol.% and can be conjugated. There can also be present further polymeric, oligomeric, dendritic or low molecular compounds. Other claimed copolymers contain (i) further repeat units imparting blue or no fluorescence, especially units improving hole- or electron-injection and/or -transport (e.g. triarylamine-, pyrrole-, pyridine- or quinoline-derivatives) and/or supporting singlet-triplet transfer in polymers (especially (bridging) carbazoles).Preferred Units: Unit B is an optionally substituted 1,4-phenylene-, 1,4-naphthylene-, 1,4- or 9,10-anthracenylene-, 1,6-, 2,7- or 4,9-pyrenylene-, 2,7- or 3,6- phenanthrenylene-, 4,4'-biphenylylene-, 4,4''-terphenylylene-, 4,4'-bi-1,1'- naphthylylene-, 4,4'-stilbene-, 4,4'-tolane-, 4,5-dihydropyrene-, 4,5,9,10- tetrahydropyrene-, fluorene-, spirobifluorene-, 5,7-dihydrodibenzoxepine-, cis- or trans-indenofluorene- or 9,10-dihydrophenanthrene-derivatives or bis(styryl)arylenes. Unit G is an electron-rich bis(styryl)arylene or a corresponding further structure, benzothiadiazole, quinoxaline, phenolthiazine, dihydrophenazine, bis(thienyl)arylene, oligo(thienylene), phenazine or corresponding derivatives containing oxygen instead of sulfur, especially an optionally substituted group of formulae (I) - (VI) (selected from 12 disclosed formulae);Y = O or S;Ar = 3-30C (hetero)aromatic ring system optionally substituted by F or by one or more of R, OR or NR2 with the proviso that in groups (IX) and (X) at least one Ar is an electron-rich aromatic group or is substituted by an electron- rich group;R = H, optionally cyclic 1-22C alkyl with one or more non-adjacent C atoms replaced by -O-, -S-, -CO-O- or -O-CO-O- and optionally with one or more H replaced by F, or optionally substituted 5-40C aryl with one or more C replaced by O, S or N; andp = -5.Unit R is a combination of electron-rich units and green-emitting electron-poor units or an aromatic system with at least 4 condensed aromatic rings or a conjugated Push-Pull system or a squalene or a quinacridone, especially an optionally substituted group of formula (XIII) - (XV) (selected from 8 disclosed formulae).Y and R = as above for (I) - (VI).Units B, G and R show can electrophosphorescence instead of electrofluorescence and can contain elements of atomic number above 36, especially Group 8-10 elements (Ru, Os, Rh, Ir, Pd, Pt) More than one unit B and/or G can be present, the total amount of G being a maximum of 3 mol.% and/or more than one unit R can be present with the total amount of R being a maximum of 1 mol.%. EXAMPLE - A copolymer of Mw 317 kDa and Mn 101 kDa prepared by Suzuki coupling as per WO2003048225 and with units of formulae M1 (50 mol.%), M5 (39.88 mol.%), M6 (0.1 mol.%), M8 (0.02 mol.%) and M9 (hole conductor; 10 mol.%) had the following electroluminescence properties : maximum efficiency = 8.25 cd/A; voltage for 100 cd/m2 brightness = 4.2 V; CIE color coordinates = 0.40/0.41; and life until 50% of original brightness = 2500 hours.