Substitution-controlled ultrafast excited-state processes in Ru–dppz-derivatives

Abstract

Ru-dppz (dppz = dipyrido[3,2-a:2',3,3'-c]phenazine) complexes play an important role as environmentally sensitive luminescence sensors and building blocks for larger supramolecular compounds. Their photophysical properties are known to be highly sensitive to intermolecular solvent-solute interactions and solvent bulk-properties. Here, the synthesis and characterisation of a novel Ru-dppz derivative is reported. The potential of drastically tuning the photophysical properties of such complexes is exemplified, by introducing very simple structural modifications, namely bromine, into the dppz-ligand scaffold. The photophysics i.e. nature of excited states and the excited-state relaxation pathway of the various complexes has been investigated by means of electrochemical measurements, steady-state emission experiments and femtosecond time-resolved spectroscopy. It could be shown that the location of bromine substitution influences the relative energy between a luminescent and a non-luminescent metal-to-ligand charge-transfer state and therefore quenches or facilitates transitions between both. Hence it is illustrated that the luminescent properties and the underlying ultrafast excited-state dynamics of the complexes can be controlled by structural variations, i.e. by intramolecular interactions as opposed to changes in the intermolecular interactions.

Tuning of Photocatalytic Hydrogen Production and Photoinduced Intramolecular Electron Transfer Rates by Regioselective Bridging Ligand Substitution

“…Furthermore, a shoulder becomes visible at longer wavelengths, that is, at approximately 484 nm. The appearance of this shoulder is in agreement with studies on the related [(tbbpy) 2 Ru(dppz-2,7- [25] and reveals the presence of two distinct MLCT states which are populated upon photoexcitation of 1. These states are associated with the two different ligands tbbpy and tpphz.…”

“…This finding is in line with literature reports on the luminescence properties of related Ru II -polypyridine complexes. [25] Ultrafast Experiments…”

Oxygen and temperature sensitivity of blue to green to yellow light-emitting Pt(ii) complexes

“…In contrast, the lifetimes of heteroleptic Pt(II) or Ir(III) complexes are in the range from 1 to 10 μs and are perfectly suited for timeresolved fluorescence detection and imaging, and in addition, they exhibit much higher quantum yields, photostabilities and sensitivities than related Ru(II) polypyridyl complexes. 1,[10][11][12] Contrary to the latter, Pt(II) or Ir(III) complexes offer a tremendous ability for color tuning due to overlapping metal-ligand charge transfer (MLCT) transitions. 1,11,12 Therefore, Pt(II) and Ir(III) complexes surpass the established luminescent oxygensensitive probes with respect to color tunability, brightness, sensitivity, dynamic range, and photostability.…”

Probing the excited state nature of coordination complexes with blended organic and inorganic chromophores using vibrational spectroscopy

“…This has been shown to be true for [Ru(L1)2(Y2-dppz-X2)] 2+ (L1 = bpy, 4,4'-tert-butyl-bpy), which have been studied using resonance Raman and luminescence spectroscopy. A prolonged excited-state lifetime was found when Y = Br, compared to Y = H; [148,158] conversely, for X = Br, both the excited state lifetime and luminescence quantum yield decreased. In both cases this can be attributed to preferential population of the substituted portion of the ligand.…”

“…A number of different substitution patterns and additional metals have been explored aside from those discussed here, [159] [38,148,158,160] and these can be used to further fine-tune the excited states formed and their lifetimes.…”