502622-88-0Relevant articles and documents
Chromium(III) Bis-Arylterpyridyl Complexes with Enhanced Visible Absorption via Incorporation of Intraligand Charge-Transfer Transitions
Barbour, Johanna C.,Kim, Amy J. I.,DeVries, Elsemarie,Shaner, Sarah E.,Lovaasen, Benjamin M.
, p. 8212 - 8222 (2017/07/22)
A series of chromium(III) bis-arylterpyridyl complexes containing intraligand charge-transfer (ILCT) excited states were prepared and characterized. These complexes show significant absorption in the visible region due to the ILCT bands. The ILCT bands are tunable across the UV and visible spectrum via incorporation of electron-withdrawing and electron-donating groups on the aryl ring. The absorption of Cr(4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine)23+ (4) in particular is much stronger in the visible region (? = 11 900 M-1 cm-1 at 450 nm and ? = 5090 M-1 cm-1 at 500 nm) than that of the parent complex Cr(tpy)23+ (tpy = 2,2′:6′,2″-terpyridine; ? = 2160 M-1 cm-1 at 450 nm, and ? = 170 M-1 cm-1 at 500 nm). Emission experiments on this series reveal Cr(III)-based phosphorescence with lifetimes from 140 to 600 ns upon excitation into the ILCT bands, which indicates funneling of the excitation energy from ligand-localized excited states to Cr(III)-based excited states. Cyclic voltammograms exhibit at least three reversible ligand-based reductions. The first reduction shows shifts of up to -160 mV compared to Cr(tpy)23+. The excited-state reduction potential of these complexes ranges from +0.95 to +1.04 V vs the ferrocene/ferrocenium couple, making them potent photooxidants.
The synthesis of 4′-aryl substituted terpyridines by Suzuki cross-coupling reactions: Substituent effects on ligand fluorescence
Goodall, Wendy,Wild, Kerstin,Arm, Kathryn J.,Williams, J.A. Gareth
, p. 1669 - 1681 (2007/10/03)
Several 4′-aryl-substituted 2,2′:6′,2″-terpyridines (tpy-C6H4R) have been prepared by palladium-catalysed cross-coupling of 4′-bromoterpyridine or 4′-triflate-terpyridine (triflate = trifluoromethylsulfonyloxy) with aryl boronic acids or esters, RC6H4B(OR′)2 (R = H, m-NH2, p-CHO, -NO2, -CN, -NMe2, -NPh2). The new ligand 4′-mesityl-terpyridine (mesityl = 2,4,6-trimethylphenyl) was prepared in the same way. Similarly, 4′-bromophenylterpyridine (tpy-φ-Br) has been cross-coupled with aryl halides to generate several new biaryl-substituted terpyridines (tpy-φ-C6H4R where R = H, p-CN, NMe2, NPh2), together with two related compounds with pendent 3- or 4-pyridyl groups (tpy-φ-C6H4-py). For selected compounds, the alternative coupling strategy of reaction of a terpyridine-4-boronate or terpyridine-4-phenylboronate with the appropriate aryl halide has also been investigated (e.g. to prepare tpy-φ-C6H4NO2), but was generally found to be less satisfactory. All of the compounds are fluorescent in the UV region of the spectrum, the biaryl-substituted compounds being only slightly red-shifted compared to the monoaryl systems, but with the further red-shift that accompanies protonation being more significant for the former. Fluorescence lifetimes in solution are in the range 1-5 ns. The emission spectra of the aminobiphenyl-substituted compounds (tpy-φ-C6H4NR″2, where R″ = Me or Ph) display a large red-shift with increasing solvent polarity, suggesting the involvement of an intramolecular charge transfer state, as found previously for the two analogues omitting the phenyl ring (tpy-C6H4NR″2). In contrast to the latter, however, protonation or binding of a Lewis acidic metal ion to the aminobiphenyl compounds serves to quench almost completely their emission.
