A new class of luminescent biotinylation reagents derived from cyclometalated iridium(III) and rhodium(III) bis(pyridylbenzaldehyde) biotin complexes, [Ir(pba)(2)(bpy-C6-biotin)](PF(6)) (1), [Ir(pba)(2)(bpy-TEG-biotin)](PF(6)) (2), and [Rh(pba)(2)(bpy-C6-biotin)](PF(6)) (3), together with their biotin-free counterparts [Ir(pba)(2)(bpy-Et)](PF(6)) (4) and [Rh(pba)(2)(bpy-Et)](PF(6)) (5) [Hpba = 4-(2-pyridyl)benzaldehyde, bpy-C6-biotin = 4-[(6-biotinamido)hexylaminocarbonyl]-4'-methyl-2,2'-bipyridine, bpy-TEG-biotin = 4-[(13-biotinamido-4,7,10-trioxa)tridecylaminocarbonyl]-4'-methyl-2,2'-bipyridine, bpy-Et = 4-(ethylaminocarbonyl)-4'-methyl-2,2'-bipyridine], have been synthesized and characterized and their photophysical and electrochemical properties studied. Upon photoexcitation, the iridium(III) complexes 1, 2, and 4 exhibited intense and long-lived orange-yellow luminescence in fluid solutions at 298 K and in rigid glass at 77 K. The rhodium(III) complexes 3 and 5 were weakly emissive in fluid solutions at 298 K but showed intense luminescence in low-temperature glass. In view of the structured emission profiles and the long lifetimes, the emission of all of the complexes has been assigned to a triplet intraligand ((3)IL) (pi --> pi*) (pba) excited state, which was probably mixed with some triplet metal-to-ligand charge-transfer ((3)MLCT) [dpi(Ir or Rh) --> pi*(pba)] character. To investigate the reactivity of the aldehyde groups, complex 2 was reacted with n-butylamine, resulting in the formation of the complex [Ir(ppy-CH(2)NHC(4)H(9))(2)(bpy-TEG-biotin)](PF(6)) (2a) [Hppy-CH(2)NHC(4)H(9) = 2-[4-[N-(n-butyl)aminomethyl]phenyl]pyridine]. All of the aldehyde complexes have been used to biotinylate bovine serum albumin (BSA) to form bioconjugates 1-BSA-5-BSA. The bioconjugates have been isolated, purified, and characterized and their photophysical properties studied. Upon photoexcitation, all of the bioconjugates were luminescent and the emission has been attributed to a (3)MLCT [dpi(Ir) --> pi*(N(wedge)N)] state for the iridium(III) conjugates and a mixed (3)IL (pi --> pi*) (N(wedge)N and N(wedge)C)/(3)MLCT [dpi(Rh) --> pi*(N(wedge)N)] state for the rhodium(III) conjugates. The avidin-binding properties of complexes 1, 2, 2a, and 3 and bioconjugates 1-BSA-3-BSA have been investigated using the 4'-hydroxyazobenzene-2-carboxylic acid assay. Emission titrations showed that complex 2a displayed a significant change of the emission profile upon binding to avidin. Additionally, the cytotoxicity of all of the iridium(III) and rhodium(III) complexes toward the human cervix epithelioid carcinoma cells has been examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide assay. Furthermore, the cellular uptake properties of the complexes and bioconjugate 2-BSA have been investigated by laser-scanning confocal microscopy.

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 ...

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 ...

A new class of luminescent cyclometalated iridium(III) polypyridine fluorous complexes has been designed; the fluorous pendant not only plays an important role in the photophysical and biological properties of the complexes, but also allows the facile isolation of biomolecules labeled with these complexes with fluorous solid-phase extraction (FSPE).

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