Organic molecules are the proficient materials which have been used in organic light emitting diodes (OLEDs). Developing new OLED materials with improved performance is the main goal of this book. One of the common electroluminescent and highly fluorescent complex is meridional isomer of tris(8-quinolinolato)aluminum (mer-Alq3) which is generally used in OLEDs. We have designed mono- and di-substituted derivatives with improved stability and mobility by substituting the EDGs and EWD groups at different position on the ligands. To design innovative and novel optical materials with high intrinsic mobility, new derivatives were designed and push-pull effect was investigated. We shed light on the geometric, electronic, photophysical and charge transfer properties of different designed materials. On the basis of electrostatic energy potential, we explained the stability of designed materials. We have explained the distribution of HOMO and LUMO on different individual ligands based on energy decomposition analysis. Blue, green, violet, yellow and red light emitters have been designed with improved stability, mobility and efficiency.