Exploitation of the Dual‐emissive Properties of Cyclometalated Iridium(III)–Polypyridine Complexes in the Development of Luminescent Biological Probes

Abstract

There has been fast-growing interest in utilizing iridium(III)-polypyridine complexes as new luminescent sensors for analytes, including protons, [1] halide ions, [2] metal cations, [3] oxygen, [4] and biomolecules. [5] These complexes display changes in their emission intensities and lifetimes upon analyte binding. Although the emission maxima exhibit small shifts in some cases, the emission profiles and spectral characteristics of the luminescent probes basically remain the same. Compared to common metal-to-ligand charge-transfer (MLCT) emitters, such as the ruthenium(II)-and osmium(II)-polypyridine systems, iridium(III)-polypyridine complexes exhibit emissive states that are very sensitive to their ligands and local environment, resulting in distinct emission features. However, it appears that this behavior has not been utilized in the current array of sensors available. Whilst dual emission is not uncommon for iridium(III)-polypyridine complexes in glass at low temperature, it is very rare in fluid solutions under ambient conditions. [5b, 6] We believe that an attractive approach to the development of new iridium-(III)-based luminescent probes would be the utilization of novel complexes that display environment-responsive dualemissive properties.Herein we report a series of novel dual-emissive cyclometalated iridium(III)-polypyridine complexes that serve as luminescent sensors for various biological receptors. The complex [Ir(ppy-CH 2 NH-C 4 H 9 ) 2 (bpy-CONH-C 2 H 5 )](PF 6 ) (1; Hppy-CH 2 NH-C 4 H 9 = 2-(4-(N-(n-butyl)aminomethyl)phenyl)pyridine; bpy-CONH-C 2 H 5 = 4-(N-(ethyl)aminocarbonyl)-4'-methyl-2,2'-bipyridine; Scheme 1) was synthesized from the reaction of the aldehyde complex [Ir(ppy-CHO) 2 (bpy-CONH-C 2 H 5 )](PF 6 ) (Hppy-CHO = 4-(2-pyridyl)benzaldehyde) with n-butylamine in refluxing methanol, followed by reduction with NaBH 3 CN. Upon irradiation, 1 exhibited intense and long-lived luminescence (Table 1).Interestingly, it showed dual emission in fluid solutions at room temperature, with a high-energy (HE) structured band at about 500 nm (t o = 1.1-2.5 ms) and a low-energy (LE) broad band/shoulder at approximately 593-619 nm (t o = 0.1-0.3 ms; Table 1). The possibility of emissive impurities in the samples was excluded on the basis of the characterization data. In degassed nonpolar solvents such as CH 2 Cl 2 , the emission intensity of the LE band was higher than or comparable to that of the HE band, whilst in more polar solvents such as CH 3 CN and CH 3 OH, it became much weaker; in aqueous buffer the spectrum was dominated by the HE band (Figure 1). [7] The intensities of both the HE and LE emission features were reduced in aerated solutions, with the former being more sensitive to quenching by oxygen. As a result, the LE band became dominant in aerated solutions, except in the case of aqueous buffer. Addition of trifluoroacetic acid (TFA) to an aerated solution of the complex in CH 2 Cl 2 shifted the LE emission band to a shorter wavelength (ca. 574 nm) and the HE feature was eventually ...

Observation of Room‐Temperature Deep‐Red/Near‐IR Phosphorescence of Pyrene with Cycloplatinated Complexes: An Experimental and Theoretical Study

“…[13][14][15] There are only very limited reports on the observation of room-temperature phosphorescence emission of pyrene [16] and its application as sensing materials, such as in luminescent oxygen sensing. [14,[17][18][19][20] Inspired by the recent elegant work on cyclometallated Pt complexes and to tackle the aforementioned challenges, [1,5,11,17,18,21] we set out to tune the emission colour of cyclometallated Pt II complexes from the typical green to deep-red/near-IR in order to achieve the room-temperature phosphorescence of pyrene. The design rationale of these complexes lies in the notion that room-temperature phosphorescence of polycyclic aromatic hydrocarbons can be facilitated by the heavy-atom effect of Pt.…”

Dual-emissive transition-metal complexes and their applications as ratiometric photoluminescent probes

“…单一组分材料的双重发射是指分子中激发态电子 能够同时从两个不同激发态以光辐射跃迁的方式回到 基态, 包括双重荧光材料、双重磷光材料以及同时具 有荧光和磷光特性的发光材料. 双重发射材料被广泛 用于光物理研究 [1] 、传感 [2] 、成像 [3] 以及发光器件 [4] 、聚合物 [11] 、量子点 [12] 、金属有机框架 材料 [22,23] 、细胞内金属离子分析检测 [24] 以及蛋白质传 感 [25] , dpp=2,3-二(2-吡啶基)吡嗪) (图2) [29] . 其中, 配合物…”

Exploitation of Luminescent Organometallic Rhenium(I) and Iridium(III) Complexes in Biological Studies

“…Lo and co-workers designed a series of novel dual-emissive cyclometallated iridium(III) polypyridine complexes [81]. The complex [Ir(ppy-CH 2 NH-C 4 H 9 ) 2 (bpy-CONH-C 2 H 5 )] + (40) exhibits dual emission in fluid solutions at room temperature, with a high-energy (HE) structured band at ca.…”