Tunable Electrochromic Luminescence of Iridium(III) Complexes for Information Self‐Encryption and Anti‐Counterfeiting

Abstract

COMMUNICATIONand easy detection of luminescence signals, rational designs of luminescent materials that are sensitive to electrical stimuli are very important because of their promising applications for fabricating new-generation smart optoelectronic devices.Phosphorescent transition-metal complexes are an attractive candidate for stimuli-responsive luminescent materials due to their various charge-transfer excited states, including triplet metal-to-ligand charge transfer ( 3 MLCT), ligand-toligand charge transfer ( 3 LLCT), and intraligand charge transfer states. [ 33 ] These charge-transfer excited states are sensitive to external stimuli. Recently, we have reported an ionic phosphorescent Ir(III) complex [ppy 2 IrN ^ N] + PF 6 − (ppy, 2-phenylpyridine; N ^ N, 2-(2-pyridyl)benzimidazole) containing a polarizable N-H group in N ^ N ligand that displays interesting electrochromic luminescence from yellow to green near anode after applying a voltage. [ 34 ] This electrochromic luminescence is attributed to the generation of an internal electric fi eld caused by migration of anionic counterions under an applied electric fi eld, which leads to a change in excited-state properties of complex. Considering the ligand-dependent excited-state properties of Ir(III) complexes, it is very important to demonstrate whether the ECL performance can be tuned by changing the ligands of complexes and different luminescence-responsive modes to the electric fi eld can be realized, which are necessary for practical applications of the ECL materials.In this work, we designed and synthesized a series of ionic phosphorescent Ir(III) complexes [(C ^ N) 2 IrN ^ N] + PF 6 − ( Figure 1 , left) containing the same N ^ N ligand (2-(2-pyridyl)benzimidazole) and different C^N ligands, 2-(2,4-difl uorophenyl)pyridine (dfppy) for Ir1 , 2-( p -tolyl)pyridine (tpy) for Ir2 , 2-phenylquinoline (pq) for Ir3 , and 2-(thiophen-2-yl)quinoline) (tpq) for Ir4 . These complexes exhibited tunable ECL performance, and the effect of C ^ N ligands on the ECL performance was investigated in detail. The detailed synthetic routes of the complexes are given in Scheme S1 in the Supporting Information. The obtained complexes were characterized by nuclear magnetic resonance (NMR) and matrix-assisted laser desorption ionization time-of-fl ight mass spectrometry, cyclic voltammetry, UV/Vis absorption spectrometry, and steady-state and transientstate photoluminescence spectrometry Complexes Ir1 − Ir4 exhibit tunable emission colors from green to red in CH 3 CN solution (Figure 1 , middle), which are dependent on the C^N ligands. Their photophysical properties have been summarized in Table S1 in the Supporting Information. Next, we investigated their luminescence

TransPrint: A Method for Fabricating Flexible Transparent Free-Form Displays

“…This is because the change of the absorption happens on an atomic level and therefore allows EC windows to switch without visible haze [40]. Recent advances have shown EC to be usable as an anticounterfeiting method by applying electrochromic materials to paper [41]. While EC is a rather old and wellestablished technology in the field of organic chemistry, it has so far mostly been neglected for HCI research [4,38,39].…”

Electroluminochromic Materials and Devices Based on Metal Complexes

“…As eries of ionic phosphorescent Ir III complexes Ir-2-Ir-5 ( Figure 2) were reported. [56] They possessed the same N^N ligand (2-(2-pyridyl)benzimidazole) and different C^N ligands, including 2-(p-tolyl)pyridine, 2-(2,4-difluorophenyl)-pyridine, 2-(thiophen-2-yl)quinoline) and 2-phenylquinoline. The emission colors of Ir-2-Ir-5 changed from green to red in acetonitrile solution prior to the voltage applied, and those of Ir-2-Ir-4 near the cathode becamed ark green, green, and orange red, respectively,b ya pplying av oltage of 8V ,w hich were dependent on the change of the HOMO-LUMO level caused by the different C^N ligands( Figure 4).…”

“…ELC responses, emission spectraand changes of energy level for (a) Ir-2,(b) Ir-3,(c) Ir-4 and(d) Ir-5 in acetonitrile before and after the voltage of 8Vwas applied. Reproduced with permission from Ref [56]…”

First observation of reversible mechanochromism and chromaticity study on calcium–copper–titanate

“…The chromism induces irreversible or reversible changes in the colors of certain compounds caused by some form of stimulus such as temperature, electric field, magnetic field, mechanical force, vapor, or solvent. 5 The color change of material under mechanical actions such as grinding, crushing, and milling is called mechanochromism. Materials which are stimuli-responsive are referred to as "intelligent material."…”

“…4 Electrochromic luminescent materials have found applications for information self-encryption, anti-counterfeiting, and fabricating new-generation smart optoelectronic devices. 5 The color change of material under mechanical actions such as grinding, crushing, and milling is called mechanochromism. At a recent time, this phenomenon has been broadly deliberate for its prospective applications in biomimetic camouflage devices and strain sensors.…”