Abstract
Pd-catalyzed Sonogashira cross-coupling reactions were used to synthesize novel π-conjugated oligothienylene-ethynylene dendrons and their corresponding terpyridine-based ligands. Their complexation with Ru(II) led to interesting novel metallodendrimers with rich spectroscopic properties. All new compounds were fully characterized by 1H and 13C NMR, as well as MALDI–TOF mass spectra. Density functional theory (DFT) calculations performed on these complexes gave more insight into the molecular orbital distributions. Photophysical and electrochemical studies were carried out in order to elucidate structure–property relationships and the effect of the dendritic structure on the metal complexes. Photophysical studies of the complexes revealed broad absorption spectra covering from 250 to 600 nm and high molar extinction coefficients. The MLCT emission of these complexes were significantly red-shifted (up to 115 nm) compared to the parent [Ru(tpy)2]2+ complex.
Highlights
Research concerning the design, characterization and application of organic semiconductors is carried out intensively due to the attractive prospects of their application in organic and molecular electronics [1,2,3,4,5]
A modular approach was selected for the synthesis of the targeted metallodendrimers, consisting of (1) the preparation of dendrons by employing Sonogashira cross-coupling reactions, (2) their functionalization with tpy-ligands, and (3) formation of the corresponding homoleptic Ru(II) complexes
Tpy 5 was synthesized starting from the corresponding tpy-triflate 3, which was obtained from 4'-hydroxy-2,2':6',2''-terpyridine in 74% yield according to a literature procedure [46]
Summary
Characterization and application of organic semiconductors is carried out intensively due to the attractive prospects of their application in organic and molecular electronics [1,2,3,4,5]. Thiophene-based oligomers and polymers are amongst the best-studied π-conjugated systems in the past few decades because of their tunable optoelectronic properties [6,7,8]. Transition-metal complexes offer significant advantages such as long-lived luminescent excited states, high chemical and photochemical stabilities, and tunability of the excited-state energies [9]. They can be employed as energy donor or acceptor units in electronic energy transfer processes [10]. Ruthenium(II) polypyridine complexes have been extensively studied and represent an area.
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