Two blue‐emitting cationic iridium complexes with 2‐(1H‐pyrazol‐1‐yl)pyridine (pzpy) as the ancillary ligands, namely, [Ir(ppy)2(pzpy)]PF6 and [Ir(dfppy)2(pzpy)]PF6 (ppy is 2‐phenylpyridine, dfppy is 2‐(2,4‐difluorophenyl) pyridine, and PF6− is hexafluorophosphate), have been prepared, and their photophysical and electrochemical properties have been investigated. In CH3CN solutions, [Ir(ppy)2(pzpy)]PF6 emits blue‐green light (475 nm), which is blue‐shifted by more than 100 nm with respect to the typical cationic iridium complex [Ir(ppy)2(dtb‐bpy)]PF6 (dtb‐bpy is 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine); [Ir(dfppy)2(pzpy)]PF6 with fluorine‐substituted cyclometalated ligands shows further blue‐shifted light emission (451 nm). Quantum chemical calculations reveal that the emissions are mainly from the ligand‐centered 3π–π* states of the cyclometalated ligands (ppy or dfppy). Light‐emitting electrochemical cells (LECs) based on [Ir(ppy)2(pzpy)]PF6 gave green‐blue electroluminescence (486 nm) and had a relatively high efficiency of 4.3 cd A−1 when an ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate was added into the light‐emitting layer. LECs based on [Ir(dfppy)2(pzpy)]PF6 gave blue electroluminescence (460 nm) with CIE (Commission Internationale de L'Eclairage) coordinates of (0.20, 0.28), which is the bluest light emission for iTMCs‐based LECs reported so far. Our work suggests that using diimine ancillary ligands involving electron‐donating nitrogen atoms (like pzpy) is an efficient strategy to turn the light emission of cationic iridium complexes to the blue region.
Charge-transfer complexes are formed by the weak association of two molecules or molecular subgroups, one of which acts as an electron donor and the other as an electron acceptor.[1] The formation of charge-transfer complexes is always driven by a combination of charge-transfer interactions and other noncovalent interactions, such as host-guest interactions and hydrophobic interactions.[2] One characteristic of charge-transfer complexes is their high charge-carrier densities, which lead to high conductivity. From this point of view, one-dimensional nanostructures that facilitate the directional movement of charge carriers are extremely important for the promising application of charge-transfer complexes as organic nanowires in electronic and optoelectronic nanodevices.[3] Typically, charge-transfer complexes are prepared by solid-phase reactions or self-assembly in nonpolar solvents (but rarely in water) because of the generally low solubility of the charge-transfer components.[4] Examples of water-soluble organic charge-transfer complexes based on viologen and pyrene derivatives have been reported for applications such as glucose sensors and guanosine triphosphate (GTP) detectors.[5] Inspired by their easy preparation and the use of water as an environmentally friendly solvent, we wondered if we could directly obtain nanoscale materials based on one-dimensional charge-transfer complexes by selfassembly in aqueous solution. However, this concept is very challenging, since the accurate stoichiometry and detailed supramolecular structure of the charge-transfer complex would not be fully revealed. Moreover, the complex formation is simultaneously affected by Coulombic attractions and charge-transfer interactions, but the dominant driving force is unclear, thus strongly hindering further application in supramolecular soft materials. Supramolecular amphiphiles are amphiphilic building blocks that are assembled by noncovalent interactions. [6] Herein, we attempt to extend the concept of "supramolecular amphiphiles" for the fabrication of one-dimensional ultralong nanofibers on the basis of the water-soluble charge-transfer complex formation between viologen derivatives and the 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (PYR). Notably, the straightness of the nanofiber can be tuned by changing the pH of the reaction solution. Furthermore, the detailed supramolecular structure is revealed, and the dominant driving force of the viologen-PYR complex is clarified. As shown in Scheme 1, a viologen-containing amphiphile (RV) was designed and synthesized. PYR is a water-soluble pyrene derivative, and is a strong electron donor. PYR and RV are expected to form a supramolecular amphiphile driven by the charge-transfer-complex formation between the PYR and the viologen. One advantage is that the supramolecular PYR-RV complex can be readily prepared by the direct mixing of PYR and RV in aqueous solution.When dissolved in aqueous solution, RV itself selfassembles into an aggregate because of its amphiphilic nature. The a...
Despite the great potential for applications spanning from military night-vision displays and information-secured devices to civilian medical diagnostics and phototherapy, the development of highly efficient, stable, and low-cost near-infrared (NIR) emitting lumophores is still a formidable challenge. Herein, we report two novel NIR-emitting homoleptic facial Ir(III) complexes based on extended π-conjugated benzo[g]phthalazine ligands, namely, tris[1,4-di(thiophen-2-yl)benzo[g]phthalazine] iridium(III) (Ir(dtbpa)3, 1) and tris[1-(2,4-bis(trifluoromethyl)phenyl)-4-(thiophen-2-yl)benzo[g]phthalazine] iridium(III) (Ir(Ftbpa)3, 2). Actually, these two ligands not only enable simple one-pot synthesis of homoleptic Ir(III) complexes without any catalyst under mild conditions, but also contribute to intense NIR-emission with high photoluminescence quantum yield up to 5.2% at 824 nm for 1 and 17.3% at 765 nm for 2, respectively. Single-crystal structure of 1 demonstrates desired facial form with short Ir–N and Ir–C bonds because of strong coordination and small steric hindrance of those highly conjugated C^NN ligands. Importantly, the incorporation of CF3 groups in 2 further leads to high thermal stability and a good ability to sublime, thus resulting in ultrapurity for highly efficient NIR-organic light-emitting diodes (NIR-OLEDs) with a high maximum external quantum efficiency of 4.5% at 760 nm and small efficiency roll-off remaining of 3.5% at 100 mA cm–2, values which rank with those of the most efficient NIR-OLEDs with small roll-off and peak emission over 750 nm. Notably, the content percentages of the noble metal in these two complexes (∼10% Ir) are markedly lower by about two-thirds than that of typical green-emitting tris(2-phenylpyridine)iridium (∼30% Ir). The findings may provide a new strategy to develop robust NIR emitters and achieve high efficiency, small roll-off, and low cost simultaneously in NIR-OLEDs for practical applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.