Two novel homometallic Ru−Ru and heterometallic Ru−Os dimers and trimers, [MII(bpy)2(4‐tpy‐4′‐methyl‐2,2′‐bipyridine)MII(tpy)]4+ and [MII(bpy)2](4‐tpy‐4′‐tpy‐2,2′‐bipyridine)(MII(tpy))2]6+, have been first prepared and characterized. Electrochemical properties of the metal‐based reversible oxidation and ligand‐based reduction are measured. Spectroscopic analysis of these complexes exhibits for every Ru‐ or Os‐based subunit an individual intense absorption spectrum extended over the entire UV and visible region. The heteronuclear complexes [RuII(bpy)2(4‐tpy‐4′‐methyl‐2,2′‐bipyridine)OsII(tpy)]4+, [RuII(bpy)2](4‐tpy‐4′‐tpy‐2,2′‐bipyridine)(OsII(tpy))2]6+, and [OsII(bpy)2](4‐tpy‐4′‐tpy‐2,2′‐bipyridine)(RuII(tpy))2]6+ display a weak emission spectrum in the near‐infrared region (NIR). The luminescence of the polynuclear assemblies is quantitatively quenched, by intramolecular energy transfer to the lower‐lying metal‐to‐ligand charge transfer (3MLCT) and metal‐centered (3MC) state of the Os(II)‐based center or Ru(II)‐terpyridine moiety at room temperature.
A cyclic (R2SnAu)3 anion (3−, R2Sn=2,2,5,5‐tetrakis(trimethylsilyl)‐1‐stannacyclopentane‐1,1‐diyl) has been synthesized as a stable blue salt with K+(THF)6 through the reaction of stable dialkylstannylene 1 with R′3PAuCl (R′=Et, Ph) followed by the reduction with KC8. Crystallographic and NMR analysis shows that the six‐membered (SnAu)3 ring of 3− is planar and highly symmetric with an equal distance of six Au−Sn bonds. A UV/Vis spectrum of 3− in hexane reveals an intense absorption maximum at 598 nm. While cyclic Au3− with four valence electrons is known as unstable anti‐aromatic anion, 3− with three divalent tin ligands is stable σ aromatic anion with an unprecedented Möbius orbital array as predicted by the perturbation MO and CCSD analysis of 3−.
Phonon
scattering with photogenerated excitons and free charges
greatly affects optoelectronic properties of metal halide perovskites
and governs their emission line width. Benefiting from the improved
phase purity, we are able to analyze exciton–phonon coupling
in 2D and quasi-2D BA2MA
n–1Pb
n
I3n+1 (n = 1–3) thin films using temperature-dependent photoluminescence
(PL) spectroscopy. The layer thickness (n value)
dependent coupling of free excitons with both acoustic and longitudinal
optical (LO) phonons was extracted quantitatively by fitting the temperature-dependent
PL line width and band gap. The low energy emissive signatures below
free excitons at low temperature might belong to the emission of self-trapped
excitons and bounded excitons in structural defects. Our findings
provide a systematic picture for the layer thickness (n value) dependent exciton–phonon coupling in 2D and quasi-2D
perovskite thin films and could be helpful for improving the optoelectronic
performance of devices made by Ruddlesden–Popper perovskite
thin films.
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