RESEARCH ARTICLE Substitutional effect of different bridging groups on optical and charge transfer properties of small bipolar molecules for OLEDs Ahmad Waqas 1 | Shamsa Bibi 1 | Shafiq‐ur Rehman 1 | Sufian Afzal 1 | Muhammad Yaseen 2 | Muhammad Shoaib 1 | Ushna Saeed 1 | Wang Da Ming 3 1 Department of Chemistry, University of Agriculture Faisalabad, Faisalabad, Pakistan 2 Department of Physics, University of Agriculture Faisalabad, Faisalabad, Pakistan 3 Alan G MacDiarmid Institute, College of Chemistry, Jilin University, Changchun, China Correspondence Shamsa Bibi and Shafiq‐urRehman, Department of Chemistry, University of Agriculture Faisalabad, Faisalabad 38000, Pakistan. Email: shamsa.shafiq@uaf.edu.pk; shafiq‐ urrehman@uaf.edu.pk Funding information Higher Education Commission (HEC) of Pakistan, Grant/Award Number: 21‐1083/ SRGP Abstract In this work, a series of eight different bipolar molecules were designed and calculated using density functional theory (DFT) and time‐dependent func- tional theory (TD‐DFT) for organic light emitting diodes (OLEDs) as efficient luminescent and charge transfer materials. The eight donor‐π‐donor type small molecules (D1‐D8) were composed of triphenylamine (TPA) donor (D) unit connected to 1,8‐naphthalimides (NI) acceptor (A) unit though different π‐con- jugated or R‐groups (as π‐spacer). The effect of substitutions made in π‐spacer was investigated on optical, electronic, and stability properties. This calculation analysis showed that different substitutions in π‐spacer resulted smaller Eg (range from 1.63 to 2.00 eV), broader absorption with the lowest excitation energy covering both visible and near infrared regions of solar spectrum, espe- cially D3, D4, D5, and D6 molecules. The analyses of local densities of states, frontier molecular orbitals, and natural population analysis of orbitals revealed that studied molecules exhibited π‐π* electronic transitions of absorption in singlet excited states, but D5 and D6 also show intramolecular charge transfer (ICT) characteristics. The study of chemical indices, molecular electrostatic potential (MEP) surfaces, and charge transfer properties turned out that D4, D5, and D6 are expected to show good potential for luminescent and hole transport materials in the favor of OLEDs. KEYWORDS absorption spectra, DFT, electronic structures, optical properties, organic light emitting diodes (OLEDs) 1 | INTRODUCTION Nowadays, renewable energy sources and low‐cost elec- tronic devices are key topics in the fields of both industrial and academic research. The sustainable development of new electronic technology with utilization of less electric- ity is a global challenge. [1–6] In this regard, a latest valuable example of technology is organic light emitting diodes (OLEDs). OLEDs have been recognized as the shining stars in discipline of technology revolution like in lighting and digital display technologies. [7–12] With the passage of time, the electric power demand is increasing in the developing countries, where a large quantity is con- sumed in buildings for lighting purposes (about 27% to 30% estimated). This challenge can significantly be reduced by rapid adoption of extremely efficient OLEDs Received: 3 May 2019 Revised: 17 June 2019 Accepted: 24 June 2019 DOI: 10.1002/poc.4000 J Phys Org Chem. 2019;e4000. https://doi.org/10.1002/poc.4000 © 2019 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/poc 1 of 12