Herein, two copolymers, poly [(6,6,12,12-tetraoctylindenofluorene)-co-(2,1,3-benzothiadiazole)] (PIFL-BT) and poly [(6,6,12,12-tetraoctylindenofluorene)-co-(2,1,3- benzooxadiazole)] (PIFL-BO) were synthesized and characterized. The effect of two electron accepting moieties benzothiadiazole (BT) and benzooxadiazole (BO) in combination with common tetraalkyl substituted indenofluorene building block in the backbone of conjugated polymer is studied in detail via thermal, optical, and electrochemical characteristics. To investigate the electroluminescence characteristics, both organic light emitting diodes (OLEDs) and light emitting electrochemical cells (LECs) devices are fabricated using copolymers as an active light-emitting layer. For the OLED devices, only polymer PIFL-BT emitted yellow light with CIE coordinates of (0.43, 0.55), a maximum current efficiency (CEmax) of 0.24 cd/A, a maximum power efficiency (PEmax) of 0.11 lm/W and a maximum brightness (MBmax) of 1398 cd/m2. For the LEC device, both materials showed light emission and higher current density than OLEDs devices, indicating better carrier injection in LECs.