Intramolecular Singlet and Triplet Energy Transfer in a Ruthenium(II) Diimine Complex Containing Multiple Pyrenyl Chromophores

Abstract

We report the synthesis and the photophysical properties of UV light-harvesting arrays constructed around a [Ru(bpy)3]2+ core (bpy = 2,2‘-bipyridine) bearing one and three pyrenyl units in the periphery. The free ligand containing the pyrenyl unit, 4-methyl-4‘-(2-hydroxyethylpyrenyl)-2,2‘-bipyridine, displays an intense emission band centered near 400 nm with a lifetime of 264 ns, characteristic of singlet pyrene emission. The complexes [Ru(dmb)2(4-methyl-4‘-(2-hydroxyethylpyrenyl)-2,2‘-bipyridine)](PF6)2, where dmb is 4,4‘-dimethyl-2,2‘-bipyridine, and [Ru(4-methyl-4‘-(2-hydroxyethylpyrenyl)-2,2‘-bipyridine)3](PF6)2 exhibit visible emission characteristic of the [Ru(bpy)3]2+ unit, regardless of excitation wavelength. The singlet emission from the pyrene chromophores is almost quantitatively quenched by the metal-to-ligand charge transfer (MLCT) states of each respective Ru(II) complex resulting in the observation of sensitized MLCT-based emission. On account of the energetic proximity between the 3MLCT states and the 3pyrene states, a long-lived 3MLCT emission is observed which decays with the same first-order lifetime as the pyrene triplet states in deaerated CH3CN. In deaerated CH3CN, the bichromophoric system displays a lifetime of 2.96 μs, whereas the tetrad complex exhibits a lifetime of 9.0 μs. The results are indicative of excited-state equilibrium between the 3MLCT and 3pyrene states. Our findings demonstrate rapid and efficient singlet−singlet energy transfer through the antenna effect whereas the reversible triplet−triplet energy transfer processes help sustain long-lived MLCT excited states.

Pendant Homopolymer and Copolymers as Solution-Processable Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

“…The singlet energy is estimated from the onset of the broad 14 emission band, which provides a more comparable result, as demonstrated by previous studies. 38 The contribution of delayed fluorescence (DF) to the overall emission is shown in Figure 6 for all the polymers. The data were obtained from the integral of the prompt and delayed fluorescence, determined from the luminescence decay obtained in vacuum because the pristine films are not permeable to oxygen diffusion.…”

Photochemical Upconversion: Anthracene Dimerization Sensitized to Visible Light by a RuII Chromophore

“…[4] The phenyl protons also display characteristic chemical shifts in comparison with those in the parent An structure. The bridgehead carbons show a resonance at d = 53.66 ppm in the 13 C NMR spectrum, which confirms the conversion to the [4+4] dimerized structure.…”

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

“…One of the earliest reports on the substitution of polypyridyl ligands with independent chromophores was by Tyson et al [167,168] in which it was shown that the incorporation of coumarin-based dyes into ruthenium complexes ( Figure 10) could deliver long-lived excited states and large oscillator strengths. [169][170][171] This was further developed using perylene and naphthalimide groups.…”