Photophysics of Ruthenium(II) Complexes with Thiazole π-Extended Dipyridophenazine Ligands

Abstract

Transition-metal-based donor–acceptor systems can produce long-lived excited charge-transfer states by visible-light irradiation. The novel ruthenium­(II) polypyridyl type complexes Ru1 and Ru2 based on the dipyridophenazine ligand (L0) directly linked to 4-hydroxythiazoles of different donor strengths were synthesized and photophysically characterized. The excited-state dynamics were investigated by femtosecond-to-nanosecond transient absorption and nanosecond emission spectroscopy complemented by time-dependent density functional theory calculations. These results indicate that photoexcitation in the visible region leads to the population of both metal-to-ligand charge-transfer (1MLCT) and thiazole (tz)-induced intraligand charge-transfer (1ILCT) states. Thus, the excited-state dynamics is described by two excited-state branches, namely, the population of (i) a comparably short-lived phenazine-centered 3MLCT state (τ ≈ 150–400 ps) and (ii) a long-lived 3ILCT state (τ ≈ 40–300 ns) with excess charge density localized on the phenazine and tz moieties. Notably, the ruthenium­(II) complexes feature long-lived dual emission with lifetimes in the ranges τEm,1 ≈ 40–300 ns and τEm,2 ≈ 100–200 ns, which are attributed to emission from the 3ILCT and 3MLCT manifolds, respectively.

A Combined Spectroscopic and Theoretical Study on a Ruthenium Complex Featuring a π‐Extended dppz Ligand for Light‐Driven Accumulation of Multiple Reducing Equivalents

“…That the signals are zero in the range of the ground state absorption, i.e ., between 400 and 470 nm, can be attributed to relatively strong ESA features, which cancel the ground state bleaching (GSB) contributions. This is typically associated with the population of 3 ππ* states for Ru(II) complexes bearing linear expanded dppz ligands [21,41–44] . In those states, the excess electron density is localized on the π‐extended chromophore, i.e ., the pq‐moiety in case of Ru .…”

“…This is manifested in the build‐up of signals between 400 and 480 nm (cancellation of GSB) and the decay of signals centered at 520 nm. The latter ESA feature is typically associated with 3 MLCT states with excess electron density on the phenanthroline sphere of the dppz ligand [35,43,44,48,50] . The second process in the MLCT excited state branch (associated with k 3 ) is ascribed to the non‐radiative decay of the 3 MLCT prox states back to the ground state.…”

Synthesis, crystal structures, DNA interactions, and antitumor activity of two new dinuclear copper(ii) complexes with thiazole ligand

“…The dark green triangular prism solidied aer two months, resulting in well-formed green crystals suitable for XRD. The nal yield was 35 2.3. Methods 2.3.1.…”

“…31 Thiazole derivatives, due to their electron donation properties with their nitrogen-containing heterocyclic, are commonly used as dinuclear 32,33 or mononuclear 34 ligands to synthesize multi-functional thiazole metal complexes with transition metal. 35,36 Thiazole metal complexes are widely used in medicine, 37 optical materials, 38 and agriculture. 39 New antitumor drugs may be developed if aromatic carboxylic acid and thiazole are both used as ligands to synthesize copper(II) complexes.…”

Pyrimidoquinxoalinophenanthroline opens next chapter in design of bridging ligands for artificial photosynthesis

“…We associate these findings with a non-radiative decay of a subset of both, 3 MC (metalcentered) and 3 MLCTpy states as typically observed for π-extended [(tbbpy)2Ru(phen)] 2+ -type complexes. [71][72][73][74][75] Ultimately, a long-lived excited 3 MLCT state, with excess electron density on the tbbpy ligands (Rupqp) or both, the phen and tbbpy moieties (Rudpymp) is populated by the process associated with τ2. These increased contributions of the phen moiety on long-lived excited state agrees with the blue-shift of the emission maximum of Rudpymp compared to Rupqp.…”