Tailoring Optoelectronic Properties of Phenanthroline‐Based Thermally Activated Delayed Fluorescence Emitters through Isomer Engineering

Abstract

Three isomeric phenanthroline compounds, namely o-PXZP, m-PXZP, and p-PXZP, are constructed by incorporating electron-donor phenoxazine unit into ortho-, meta-, or para-positions of a rigid electron-acceptor phenanthroline core. This approach functionalizes these compounds to exhibit thermally activated delayed fluorescence (TADF) characteristics with microsecondscale photoluminescence (PL) lifetimes. Their thermal, electrochemical properties, emissive characteristics, and energy levels can be finely tailored through isomer engineering. The meta-and para-linking compounds (m-PXZP and p-PXZP) possess higher decomposition temperatures, deeper lowest unoccupied molecular orbital levels, higher PL quantum efficiencies, smaller singlet-triplet energy splitting, and reduced DF lifetimes relative to their ortho-disposition isomer (o-PXZP). Consequently, a green fluorescence organic light-emitting diode (OLED) based on m-PXZP achieves a maximum external quantum efficiency of 18.9%, and has a slow efficiency roll-off of 28% at the luminance of 1000 cd m −2 . Notably, m-PXZP-based device exhibits a nearly 100% utilization efficiency of electro-generated singlet and triplet excitons. These results demonstrate for the first time that phenanthroline derivatives can be employed as TADF emitters for high-efficiency OLEDs. The isomer engineering for TADF emitters provides a simple method to extend structure diversity of TADF emitters, and moreover it provides a flexible method to optimize optoelectronic properties and thereby manipulate electroluminescence performance.

Isomerization Strategy of Nonfullerene Small‐Molecule Acceptors for Organic Solar Cells

“…[1][2][3][4][5] Solution-processed bulk-heterojunction (BHJ) organic solar cells (OSCs) have emerged as a promising contender of conventional silicon-based solar cells in virtue of their advantages, such as low carbon footprint, short energy payback time, low temperature processing and easy fabrication into flexible, lightweight, and semitransparent devices, [6][7][8][9][10][11][12] where BHJ refers to blended electron donor and acceptor materials in the active layer of OSCs. [13][14][15][16][17][18] Fullerene acceptors, particularly [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) were widely used as electron acceptors, as they exhibit 3D character and delocalized lowest unoccupied molecular Orbital (LUMOs), high electron mobility, and the ability of coconstructing interpenetrating network with donors, which is favorable for charge light-emitting diodes (OLED) [67][68] and perovskite solar cells (PVSC). [69][70] Recently, the isomeric strategy has been exploited in nonfullerene acceptors, and many highly efficient SMAs have been produced.…”

“…In this review, all the representative isomeric systems undermentioned belong to the class of constitutional isomers. As a matter of fact, developing constitutional isomers is an effective approach to finely tune the electronic structure, absorption spectra, charge transport, and molecular stacking, and therefore widely utilized in molecular design for organic field‐effect transistors (OFET), [ 64–66 ] organic light‐emitting diodes (OLED) [ 67–68 ] and perovskite solar cells (PVSC). [ 69–70 ] Recently, the isomeric strategy has been exploited in nonfullerene acceptors, and many highly efficient SMAs have been produced.…”

Synthesis and Electrochemical and Spectroscopic Characterization of 4,7-diamino-1,10-phenanthrolines and Their Precursors

“…The highest yield and less complex reaction mixture of 10 H -phenothiazine derivatives can be attributed to the better nucleophilic properties of 10 H -phenothiazine anion than 9 H -carbazole. Wu et al obtained the X-ray structure of 4,7-di(10 H -phenoxazin-10-yl)-1,10-phenanthroline [28], which was cocrystallized with THF as a guest molecule located in the crystalline frameworks. The THF molecule is surrounded by two 10 H -phenoxazine rings and 1,10-phenanthroline core.…”

“…The performed investigations on the X-ray studies were inspired by the work of G. Zucchi et al and K.J. Shaffer et al [25,28]. Presented here compounds crystalize in the triclinic P –1 space group as a solvate with two CHCl 3 molecules 5d and two THF and one methanol molecules in the case of compounds 6a and 6b crystalizes in monoclinic P 2 1 /c space group with two THF molecules.…”

Modulation of Thermally Activated Delayed Fluorescence in Waterborne Polyurethanes via Charge‐Transfer Effect

“…In the past decades, purely organicl uminescentm aterials have experienced ab ooming development due to their enormous applicationsi nc hemical sensors, [1][2][3][4] optoelectronics, [5][6][7][8][9] bioimaging [10][11][12][13][14][15] and data storage. [16][17][18][19][20][21] Especially,t hermally activated delayed fluorescence( TADF), [22][23][24][25][26] discovered as the second band of long-lived emission, shows identical contour with the prompt fluorescence( PF) and has been widely used in organic light-emitting diodes (OLEDs).…”