Twisted Phenanthro[9,10-d]imidazole Derivatives as Non-doped Emitters for Efficient Electroluminescent Devices with Ultra-Deep Blue Emission and High Exciton Utilization Efficiency

Herein, two deep-blue emissive molecules ( SAF-PI and SAF-DPI ) are designed and synthesized using spiro[acridine-9,9’-fluorene] as a donor (D) substituted with 2-(3-methylphenyl)-1-phenyl-phenanthro[9,10-d]imidazole as an acceptor (A), forming twisted D−A and A−D−A structures, respectively. The photophysical studies and density functional theory (DFT) calculations reveal that both molecules exhibit hybridized local excited and charge transfer (HLCT) characteristics with deep blue emission color. They are effectively applied as non-doped emitters in OLEDs. Particularly, SAF-PI -based device achieves the high-definition television (HDTV) standard blue color emission peaked at 428 nm with CIE coordinate of (0.156, 0.053), a narrow full width at half maximum of 55 nm, a maximum external quantum efficiency (EQE_max) of 4.57% and an exciton utilization efficiency of 65%.     

Rational Design of Chrysene-Based Hybridized Local and Charge-Transfer Molecules as Efficient Non-Doped Deep-Blue Emitters for Simple-Structured Electroluminescent Devices

Herein, we present a molecular design of chrysene-based deep-blue emissive materials ( TC , TpPC , TpXC , and TmPC ), in which chrysene as a core is functionalized with different triphenylamine moieties to realize a fine-tuning deep-blue fluorescence with superior electroluminescent (EL) performance. The photophysical analyses and density functional theory (DFT) calculations disclose that TC , TpPC , and TpXC possess HLCT characteristics with intense deep-blue emission in the solid-state, good hole-transporting ability, and high thermal and electrochemical stabilities. They are successfully employed as non-doped emitters in simple structured OLEDs (ITO/PEDOT : PSS : NF/emitter/TPBi/LiF : Al). In particular, TC -based device emits a deep-blue light with an emission peak at 446 nm and CIE color coordinates of (0.148, 0.096), a maximum external quantum efficiency (EQE_max) of 4.31%, and a low turn-on voltage of 2.8 V.     

Fourfold alkyl wrapping of a copper(II) porphyrin thwarts macrocycle π–π stacking in a compact supramolecular package

Porphyrins are valuable constituents in optoelectronic, catalytic, and other applications, yet control of intermolecular π–π stacking is invariably essential to attain the desired properties. Superstructures built onto the porphyrin, often via meso‐aryl groups, can afford facial encumbrance that suppresses π–π stacking, although some molecular designs have provided insufficient facial coverage and many have entailed cumbersome syntheses. In this study, a copper(II) porphyrin bearing four meso substituents, namely, {10,20‐bis[2,6‐bis(octyloxy)phenyl]‐5,15‐dibromoporphinato}copper(II), [Cu(C₆₄H₈₂Br₂N₄O₄)], was prepared by metalation of the corresponding free‐base porphyrin and was characterized by single‐crystal X‐ray diffraction. The crystal structure reveals a dihedral angle of 111.1 (2)° for the plane of the meso‐aryl group relative to the plane of the porphyrin, with both aryl groups tilted in the same direction. Each of the four octyloxy groups exhibits a gauche conformation for the –OCH₂CH₂– unit but is extended with four or five anti (–CH₂CH₂–/H) conformations thereafter, causing each octyl group to span the dimension of the macrocycle. In a global frame of reference where the two Br atoms define the north/south poles and the two aryl groups are at antipodes on the equator, two octyl groups of one aryl unit project over the northern hemisphere (covering pyrroles A and B), whereas those of the other aryl unit project over the southern hemisphere (covering pyrroles C and D). Together, the four octyl groups ensheath the two faces of the porphyrin in a self‐wrapped assembly. The closest approach of the Cu atom to an octyl methylene C atom (position 6) is 3.5817 (18) Å, the mean separations of neighboring porphyrin planes are 8.059 (4) and 4.693 (8) Å along the a and c axes, respectively, and the center‐to‐center distances between the Cu atoms of neighboring porphyrins are 10.2725 (4), 12.2540 (6), and 12.7472 (6) Å along the a, b, and c axes, respectively. The Hirshfeld surface analysis and two‐dimensional (2D) fingerprint plots provide information concerning contact interactions in the supramolecular assembly of the solid crystal.