Tuning the luminescence lifetimes of ruthenium(ii) polypyridine complexes and its application in luminescent oxygen sensing

Abstract

Ru(Phen)(bpy) 2 (1) and its new derivatives (2-5) with pyrenyl or ethynylated pyrene and phenyl units appended to the 3-position of the phenanthroline (Phen) ligand were prepared and these complexes generate long-lived room temperature phosphorescence in the red and near IR range (600-800 nm). The photophysical properties of these complexes were investigated by UV-Vis absorption, luminescence emission, transient absorption spectra and DFT/TDDFT calculations. We found the luminescence lifetime (s)can be drastically extended by ligand modification (increased up to 140-fold), e.g. s ¼ 58.4 ms for complex 3 (with pyrenyl ethynylene appendents) was found, compared to s ¼ 0.4 ms for the reference complex 1. Ethynylated phenyl appendents alter the s also (complex 2, s ¼ 2.4 ms). With pyrenyl appendents (4 and 5), lifetimes of 2.5 ms and 9.2 ms were observed. We proposed three different mechanisms for the lifetime extension of 2, 3, 4 and 5. For 2, the stabilization of the 3 MLCT state by p-conjugation is responsible for the extension of the lifetime. For 3, the emissive state was assigned as an intra-ligand (IL) long-lived 3 p-p* state ( 3 IL/ 3 LLCT, intraligand or ligand-to-ligand charge transfer), whereas a C-C single bond linker results in a triplet state equilibrium between 3 MLCT state and the pyrene localized 3 p-p* triplet state ( 3 IL, e.g. 4 and 5). DFT/TDDFT calculations support the assignment of the emissive states. The effects of the lifetime extension on the oxygen sensing properties of these complexes were studied in both solution and polymer films. With tuning the emissive states, and thus extension of the luminescence lifetimes, the luminescent O 2 sensing sensitivity of the complexes can be improved by ca. 77-fold in solution (I 0 /I 100 ¼ 1438 for complex 3, vs. I 0 /I 100 ¼ 18.5 for complex 1). In IMPES-C polymer films, the apparent quenching constant K SV app is improved by 150-fold from 0.0023 Torr À1 (complex 1) to 0.35 Torr À1 (complex 3). The K SV app value of complex 3 is even higher than that of PtOEP under similar conditions (0.15 Torr À1 ).

Synthesis and characterisation of Fe(III) and Co(III) complexes of thiazole-containing thiosemicarbazone ligands

“…[1][2][3][4] By careful choice of the metal ion a range of applications can be targeted including luminescent systems, catalysts, and magnetically interesting systems. [5][6][7][8] . [9][10][11] Thiosemicarbazonebased ligands have been used to generate interesting complexes with a range of potential applications, however one area that appeals to us is their use in Fe(III) spincrossover (SCO) systems.…”

Supramolecular complexes of cobalt(II), manganese(II) and cadmium(II) with bis(terpyridine) ligand as novel luminescent materials

“…1) 15 . The latter one is found for all the investigated compounds, irrespective of their nuclearity nor the chosen metal ion (Fig.…”

So-called “dual emission” for 3MLCT luminescence in ruthenium complex ions: What is really happening?

“…They attributed one emission feature to singlet fluorescence from a transition internal to the extended ligand and a second, longer wavelength feature to a charge transfer state formed with only modest yield following short-wavelength excitation. Also in 2010 came two more reports of extending ligand conjugation in ruthenium compounds with the goal of lowering intraligand triplet energies, increasing the lifetimes of the lowest states, and making luminescent probes that are more sensitive to oxygen concentration [40,41]. Dual emission was not reported, and is not apparent in published spectra; but it is not clear that much effort was expended in excluding the possibility of a minor component at shorter wavelengths.…”