Engineering Tunable Single and Dual Optical Emission from Ru(II)–Polypyridyl Complexes through Excited State Design

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• 作者：Julia RomanovaYousif Sadik ; M. R. Ranga Prabhath ; J. David Carey ; Peter D. Jarowski
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：February 2, 2017
• 年：2017
• 卷：121
• 期：4
• 页码：2333-2343
• 全文大小：919K
• ISSN：1932-7455

文摘

Excited state design is an efficient approach toward new applications in molecular electronics spanning solar cells, artificial photosynthesis and biomedical diagnostics. Ruthenium(II)–polypiridyl based complexes are an example of molecular building blocks with tunable single and dual wavelength emission that can be controlled by excited state engineering via selective ligand modification. Here we investigate three new heteroleptic [Ru(bpy)₂X]⁺ complex ions, where X represents pyridinyl or pyrazinyl derivatives of diazolates, providing tunable emission in the visible and infrared region. The dual emission is shown to arise from the presence of two excited states consisting of a triplet metal-to-ligand charge transfer state localized on a bipyridine ligand, ³MLCT (bpy), and a state that either is entirely localized on the X ligand or is partially delocalized also spanning part of the bipyridine ligands, ³MLCT(X). By a suitable choice of the X ligand, emission from ³MLCT(bpy) and ³MLCT (X) states can be rationally varied between 743 and 865 nm and from 555 to 679 nm, respectively. An increase in the nitrogen content of the six-membered ring of the X ligand results in a blue shift of the ³MLCT(bpy) emission but a red shift for the ³MLCT (X) emission. The wavelength difference between ³MLCT(bpy) and ³MLCT (X) emissions can be tuned from 84 to 310 nm and is proportional to the difference in LUMO energies (reduction potentials) of the isolated ligands. Our study provides key information toward new routes for the design of optically active dual wavelength molecular emitters.