Photophysical and Electrochemical Properties of Phenanthroline‐Based Bis‐cyclometallated Iridium Complexes in Aqueous and Organic Media

Abstract

The electrochemical and photophysical properties of biscyclometallated iridium(III) complexes containing phenanthroline-based ligands have been investigated and compared in organic and aqueous media. Complexes having general formula [Ir(ppy) +/-were synthesized, where ppy is the cyclometallating ligand, 2-phenylpyridine, and N _ N represents one of the following phenanthroline based ligands: 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (dpp) and 4,7-diphenyl-1,10-phenanthrolinedisulfonate (BPS). In the case of [Ir(ppy) 2 (BPS)] -, the SO 3 -group located on the phenyl ring of BPS dramatically increases the aqueous solubility of the complex compared to the dpp complex, which is only soluble in organic media. The chloride salt of the underivatized phen complex, though not as soluble as the BPS chelated complex, is sufficiently soluble (Ͼ 1 mM) for sensing and other applications in aqueous media. The electrochemical response depends markedly on the medium; all the complexes showed reversible behaviour in organic media, whereas the oxidative electrochemistry of [Ir(ppy) 2

Solvent dependent photosensitized singlet oxygen production from an Ir(iii) complex: pointing to problems in studies of singlet-oxygen-mediated cell death

“…, octan-1-ol (orange) and CH 2 Cl 2 (blue). When we expand the intensity scale of our absorption spectra in the range ~ 450-500 nm we observe a weak band that has been previously observed 32 and assigned to the population of the lowest triplet state of Ir(ppy) 2 (phen) + . Although the discussion below focuses on solvent-dependent CT effects, the preceding interpretation of the D 2 O/H 2 O solvent effect means that we cannot exclude the possibility that, to some extent, the data recorded in octan-1-ol and CH 2 Cl 2 also reflect (1) a comparatively poor coupling between Ir(ppy) 2 (phen) + and these solvents and (2) the comparative lack of vibrational modes in these solvents that can act as a sink for the excitation energy of Ir(ppy) 2 (phen) + .…”

Photophysical Properties of Oligo­(phenylene ethynylene) Iridium(III) Complexes Functionalized with Metal‐Anchoring Groups

“…[30,33,46] Interestingly, compared with those observed at room temperature, the low-temperature phosphorescence decay curves measured at λ = 560 nm for Ir1-Ir4 show biexponential decays with lifetimes for the two component differing by ca. 10 μs ( Table 2).…”

“…The topologies of the molecular orbitals of Ir2 and Ir4 ( Figure S4) are identical to those of Ir1. Similarly to those of related ppy-based cyclometallated Ir complexes, [31][32][33] the HOMO is composed of a mixture of Ir III dπ orbitals (t 2g ) and phenyl π orbitals with little contribution from the pyridine rings of the cyclometallated ligands. As the family of complexes Ir1-Ir4 only differs in the diimine ligand, the energy of the HOMO remains almost constant along the series and is slightly more stable for Ir3 and Ir4 (Figure 6, b).…”

“…[37,38,51] The absorption bands of Ir1-Ir4 are broader than those of the bare ligands 1-4 ( Figure 2 ) in the λ = 350-450 nm range. On the basis of previous reports, [28][29][30][31]33,37] we assign the first band to π→π* transitions centred on the ppy and phen ligands. The second broad band is the result of the overlap of π→π* LC transitions with spin-allowed 1 MLCT transitions.…”

“…[28,29] For example, the contribution of triplet ligand-centred ( 3 LC) excited states to the photoluminescence increases with the conjugation length. [29][30][31][32][33] In this work, we present the synthesis and characterization of a series of monocationic photoluminescent Ir III complexes (Ir1-Ir4, Figure 1), which incorporate conjugated ligands of different molecular length and are functionalized with suitable anchoring groups for their integration into metallic molecular junctions. [34,35] The new compounds result from the combination of iridium(III) bis-cyclometallated 2-phenylpyridine complexes with four different diimine π-conjugated ligands (1)(2)(3)(4).…”