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 ...

Dual Emission from Rhenium(I) Complexes Induced by an Interligand Aromatic Interaction

“…Such a unique dual-emission phenomenon is potentially applicable to emitting materials such as sensors and so on. [31] Table 4. Ratios between IR absorption intensities of the symmetric and asymmetric stretching modes of the two carbonyl groups (I asym /I sym ) in acetonitrile, the calculated C-Re-C bond angles (q calcd ) according to Equation (2), and the observed C-Re-C bond angles in the crystal (q obsd ).…”

Synthesis, crystal structure, photophysical property and electropolymerization of Pt(II) complexes with carbazole-grafting 2-(2-pyridyl)benzimidazole

“…Multi-chromophoric systems have attracted great attention for their potential applications in solar energy utilization [1], biological probe [2], optical material [3], molecular device [4], supermolecular assemble [5] and so on. Particularly, the research in white organic light-emitting diodes (WOLEDs) has already been a hot area [6].…”

“…9-butyl-carbazole (1), 9-(4-bromobutane)carbazole (2) and N-[4-(9-carbazole)butyl]-2-(2-pyridyl)benzimidazole (PBC) (4) were synthesized according to literature methods [23,24]. Platinum(II) dichloride complex (5) was obtained by stirring ligand PBC (4) and [Pt(DMSO) 2 Cl 2 ] [25] in CH 2 Cl 2 for 24 h, followed by recrystallizing from its CH 2 Cl 2 /MeOH solution [26].…”

Cyclometalated Iridium(III) Complexes with Deoxyribose Substituents

“…Yield: 0.058 g (79 %); 1 10, 157.52, 151.21, 150.41, 149.44, 149.06, 148.37, 148.13, 146.42, 143.19, 141.57, 141.32, 140.15, 137.70, 134.86, 134.56, 130.50, 130.39, 130.29, 129.83, 129.74, 129.41, 127.79, 126.92, 124.88, 124.44, 124.10, 123.85, 122.95, 122.74, 122.37, 121.30, 120.80, 91.60, 88.92, 69.79, 61.11, 42.43 ppm; UV/Vis (acetonitrile): l max (e) = 242 (14000), 315 nm (8000 m À1 cm À1 ); emission (acetonitrile): l ex (Int.) = 516 (176), 540 nm (sh, 150); HRMS: calcd for C 38 (25 mL). To this was added a solution of compound 7 (0.026 g, 0.098 mmol) in 10 mL dry THF, followed by NH 4 PF 6 (0.014 g, 0.086 mmol).…”

“…[36,37] IridiumA C H T U N G T R E N N U N G (III) complexes have also been attached to steroids, such as estradiol. [38] Lo and co-workers report that emission of two distinct iridium complexes tethered to estradiol intensifies upon binding to the receptor ERa. [39] Sugars have been conjugated to iridium complexes indirectly through tethers that end in amino-oxy moieties.…”