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.

We report on nanoindentation measurements of hydride vapor phase epitaxy (HVPE) grown Gallium Arsenide Phosphide (GaAs1-xPx) epilayers, of interest for generation of mid-infrared wavelengths via frequency conversion. Our results indicate a linear trend in Young's modulus with increasing phosphorus content (P-content), in keeping with Vegard's Law for ternary compounds. The corresponding data for hardness demonstrate significant bowing with a peak of 10.7 GPa occurring at 78 % P-content. Some epilayers exhibit non-negligible spatial variation in their mechanical properties, which is investigated with complementary measurements. Photoluminescence measurements indicate high composition uniformity, while atomic force microscopy reveals a direct correlation between surface roughness and mechanical variability. Preliminary laser-induced damage threshold (LIDT) results are reported, and the implications for material optimization are discussed. With a 1070-nm continuous wave laser, GaAs0.75P0.25 and GaAs0.52P0.48 epilayers demonstrated LID thresholds of 600 kW/cm2 and 300 kW/cm2, respectively.

In this study, spectroscopic ellipsometry was employed to characterize the optical properties of 19 different organic thin films used in the fabrication of organic light-emitting diodes (OLEDs). The films were deposited via thermal evaporation onto quartz and soda lime float glass substrates coated with a SiO 2 buffer layer and indium tin oxide (ITO). The analysis included a range of organic compounds, from widely studied materials such as CBP (4,4′-Bis(N-carbazolyl)-1,1′-biphenyl) to less-explored compounds such as TAZ (3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole), PO-T2T ((1,3,5-Triazine-2,4,6-triyl)tris(benzene-3,1-diyl)tris(diphenylphosphine oxide)), CzSi (9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole), and NBphen (2,9-Dinaphthalen-2-yl-4,7-diphenyl-1,10-phenanthroline). Attention was given to the influence of substrate material on the complex refractive index - specifically, the refractive index ( n ) and extinction coefficient ( k ) - across a broad spectral range (210-1690 nm, 0.7-5.9 eV). The results reveal critical insights into substrate-dependent variations, including the presence of refractive index gradients and anisotropic optical behavior in selected organic thin films.