In this work, OLEDs based on a new modified polymer PMC 300* (as emissive layer: EML) were manufactured with the structure ITO/PEDOT:PSS/Polymer (PMC 300*)/LiF or PFN/Al. This new polymer PMC 300*: Poly[(Benzo[c][1,2,5]thiadiazole-4,7-diylbis(9,9-dimethyl-9H-fluorene-7,2-diyl))-3,3-diyl(1-(3- (trifluoromethyl)phenyl)-2-oxindole)], is a modified version of PF-1 polymer that was synthesized and used previously in our group for non-linear optical properties and in OLED devices. The CF3 additional group on PMC 300* showed an improved electroluminescence and current efficiency on OLED devices. PF-1 and PMC 300* polymers have a fluorescence quantum yield (FLQY) of approximately 1. Film formation of the hole injection layer (HIL) and the EML were made by spin coating and subsequently evaporating LiF (or PFN by spin coating) and Al as cathode. Polymer films show a very low roughness (~ 1-2 nm), as most of the polymers used in OLEDs. Due to PMC 300* excellent properties like high solubility, very high QY, high conjugation and mechanical characteristics, OLEDs based on this new modified polymer (with emission in green-yellow wavelengths) showed luminances up to 1937 cd/m2, high current efficiencies of 35 cd/A and a maximum external quantum efficiency (EQEmax) of 2.6 %. Additionally, preliminary tests of flexible OLEDs by using this polymer are currently carrying out, results are promising.