Virtual screening of CBP derivatives for OLED applications towards evaluation of substitution effects on electronic and optical properties

The electronic structure, charge transport, and excitonic properties of organic molecules critically govern their performance in organic light-emitting diodes (OLEDs). Here, we report a systematic density functional theory (DFT) study of 55 derivatives of 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), functionalized by attaching eleven electron-donating and electron-withdrawing substituents at five distinct positions. Fundamental parameters including bandgap, ionization potential, electron affinity, quantum chemical reactivity descriptors, optical absorption, and exciton binding energies (EBEs) were rigorously evaluated. This work demonstrates that substituent identity and attachment position significantly influence molecular optoelectronic characteristics. Notably, benzo[c][1,2,5]thiadiazole substitution at the carbazole site provided an optimal bandgap (2.99 eV), low EBE (0.38 eV), and visible-range absorption (∼476 nm), ideal for emissive-layer applications. TCNQ attached at the biphenyl core exhibited the smallest bandgap (0.856 eV), highest electron affinity (4.86 eV), and maximum softness, highlighting excellent electron-transporting capabilities. Furthermore, 1,4-dicyanobenzene substitution at the biphenyl position combined balanced reactivity with electronic stability, suitable as a phosphorescent OLED host. Corroborated by Density of States profiles, molecular electrostatic potentials, and UV-Vis spectra, this work provides valuable design principles for developing next-generation high-performance OLED materials. • Systematic DFT study of 55 CBP derivatives modified by diverse electron-donating and electron-withdrawing substituents. • Identification of optimal derivatives tailored for emissive, electron transport, and host roles in OLED devices. • Benzo\[c]\[1,2,5]thiadiazole at carbazole sites exhibits ideal electronic structure for emissive layers. • TCNQ substitution at the biphenyl core enhances electron affinity and transport capability. • 1,4-Dicyanobenzene substitution at biphenyl position optimizes electronic stability for phosphorescent OLED host applications.