Excited State Processes in Ruthenium(II)/Pyrenyl Complexes Displaying Extended Lifetimes

Abstract

The synthesis and photophysical properties of two Ru(II) diimine complexes bearing one (dyad) and three (tetrad) pyrenyl units, respectively, are presented. The pyrene chromophore in each metal complex is tethered through a single C-C bond in the 5-position of 1,10-phenanthroline (py-phen). Both Ru(II) complexes display increased absorption cross sections near 340 nm largely due to the presence of the pyrenyl chromophore(s). Excitation from 300 to 540 nm results exclusively in the observation of metal-to-ligand charge transfer (MLCT) based emission that is exceptionally long lived, 23.7 µs and 148 µs in deaerated CH 3 CN, respectively. This luminescence was analyzed using steady-state and time-resolved techniques at room temperature and 77 K. The tetrad complex, [Ru(py-phen) 3 ] 2+ , displays a dynamic self-quenching reaction at room temperature in dilute CH 3 CN solutions that is well modeled by a Stern-Volmer expression. The excited-state processes occurring between the MLCT core and the pyrenyl units were further evaluated with ultrafast transient absorption spectroscopy and conventional flash photolysis. Formation of the 3 pyrene absorption was directly monitored in both complexes and ranged from 2.8 × 10 10 s -1 in [Ru(bpy) 2 (py-phen)] 2+ to 2.4 × 10 11 s -1 in [Ru(py-phen) 3 ] 2+ . In both cases, the transient absorption spectra contain features of 3 pyrene excited states, whereas the room-temperature luminescence is MLCT-based, both decaying with the same kinetics. This is consistent with the formation of a thermal excited-state equilibrium between the two triplet states at room temperature. Both Ru(II) complexes were found to sensitize the production of molecular singlet oxygen with a quantum efficiency of 0.69, measured by observing the characteristic 1 O 2 luminescence at 1270 nm.

Carbon nanotubes dispersed in aqueous solution by ruthenium(ii) polypyridyl complexes

“…Interestingly, its emission lifetime in water reaches 665 µs. In accordance with previous studies, this phenomenon is attributed to the emission from 3 [33][34][35][36] To study the interaction of RuPy complexes with a variety of nanotubes types (chiralities) we employed HiPco nanotubes. SWCNTs were dispersed in D 2 O solutions of either RuPy1 or RuPy2 with different initial amounts of HiPco SWCNTs.…”

Synthesis, Electrochemical and Optical Properties of RuII–Diphenylphenanthroline–Ethynylpyrenephenanthroline Systems

“…[4] Out of the various organic units employed, which are appended to the ligands of the first coordination sphere, pyrene has proved to be quite effective in the tuning process of Ru II -tris(bichelating) emitters, namely [Ru(bpy) 3 ] 2+ , where bpy is 2,2Ј-bipyridine. [5] Reasons are perature and in O 2 -free solvent, complex 1 appeared to be practically nonluminescent, whereas 2 exhibited intense 3 MLCT emission; quantum yields of f em = 9ϫ 10 -4 and 6.1 ϫ 10 -2 were found for 1 and 2, respectively and λ exc = 462 nm in both cases. The lowest-lying excited states of 1 were assigned as 3 LC states, which were localised on the EP moiety.…”

“…[5,6,19,22,23] As a consequence, at room temperature (295 K), thermal equilibration between these levels can be establish according to Equation (1) (1) where N Ru /N pyr denotes the population ratio of the 3 RuLCT and 3 pyr states and ∆ TT is the energy gap between them; k B T = 205.9 cm -1 (295 K). On this basis, the luminescence properties of such bichromophores can be understood with the help of Equations (2) and (3).…”

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

“…[169][170][171] This was further developed using perylene and naphthalimide groups. [172][173][174][175][176] In the case of the naphthalimide substituents both MLCT and LC π,π* states were evident. The evidence for the LC π,π* state was elegantly demonstrated using time-resolved infrared spectroscopy in the 1400 -1800 cm -1 region which showed that the transient created in [Ru(phen)2(PNI)] 2+ was identical to that from tolyl-PNI ( Figure 10).…”