Diane R. Smith

Photoinduced processes in 4′-(9-anthryl)-2,2′:6′,2″-terpyridine, its protonated forms and Zn(II), Ru(II) and Os(II) complexes

Abstract We investigated the absorption spectra and the luminescence properties of 2,2′:6′,2″-terpyridine(tpy), 4′-(9-anthryl)-2,2′:6′,2″-terpyridine (An-tpy), their protonated forms, and their Ru(II), Os(II), and Zn(II) metal complexes ([M(tpy) 2 ] 2+ and [M(An-tpy) 2 ] 2+ ). For both tpy and An-tpy, the addition of CF 3 SO 3 H to acetonitrile (or dichloromethane) solutions causes changes in the absorption spectra that indicate the formation of monoprotonated (tpyH + and An-tpyH + ) and diprotonated (tpyH 2 2+ and An-tpyH 2 2+ ) forms. The weak fluorescence of tpy ( λ max = 338 nm ) becomes much stronger and moves to lower energy ( λ max = 410 nm ) upon the first protonation, and then moves back to higher energy ( λ max = 360 nm ) upon the second protonation. An-tpy shows a strong anthracene-type fluorescence band with λ max = 422 nm which disappears upon the first protonation: the diprotonated form shows a very weak emission with λ max = 505 nm . Both the absorption and emission spectra of the protonated forms of An-tpy indicate that the lowest excited state can be assigned to a charge-transfer transition from the anthracene moiety to the protonated tpy moiety. In contrast, [Zn(tpy) 2 ] 2+ shows a very intense, ligand-centered fluorescence band with λ max = 353 nm , whereas [Zn(An-tpy) 2 ] 2+ shows that a much weaker emission with λ max = 543 nm , assigned to an An → [Zn(tpy)) 2 ] 2+ charge-transfer transition. The very weak metal-to-ligand charge transfer (MLCT) phosphorescence of [Ru(tpy) 2 ] 2+ is no longer present in [Ru(An-tpy) 2 ] 2+ because the 1 MLCT level of the Ru-based unit is quenched by the lower lying T 1 excited state of the anthracene unit, as shown by the appearance of the characteristic T 1 transient absorption band with λ max = 420 nm in flash spectroscopy experiments. In aerated solutions the T 1 excited state of the anthracene unit of [Ru(An-tpy) 2 ] 2+ is quenched by dioxygen with formation of 1 Δ (O 2 ), whose emission can be observed in the near-IR region ( λ max = 1270 nm. Continued irradiation of [Ru(An-tpy) 2 ] 2+ in aerated solution causes the destruction of the anthracene moiety because of its reaction with 1 Δ (O 2 ). [Os(An-tpy) 2 ] 2+ shows the same 1 MLCT emission as [Os(tpy) 2 ] 2+ ( λ max = 728 nm) since the 1 MLCT level lies below the T 1 excited state of the anthracene moiety. The absorption and excitation spectra of [Os(An-tpy) 2 ] 2+ are almost coincident, showing that the S 1 excited state of the anthracene unit is converted efficiently to the 1 MLCT level of the [Os(tpy) 2 ] 2+ unit.

4-tert-butylphenyl solubilized oligopyridines

Abstract Soluble 4- tert -butylphenyl substituted derivatives of 2,2′:6′,2″-terpyridine, 2,2′:6′,2″:6″,2″′-quaterpyridine, 2,2′:6′,2″:6″,2″′:6″′,2″″-quinquepyridine and 2,2′:6′,2″:6″,2″′:6″′,2″″:6″″,2″″′-sexipyridine have been prepared. The ligands and their metal complexes are more soluble than unsubstituted analogues, but the introduction of the bulky substituent does not perturb any metal centred processes.

The coordination chemistry of 4′-(4-tert-butylphenyl)-2,2′ : 6′,2″-terpyridine—a solubilising oligopyridine

Abstract The preparation of a solubilised 2,2′ : 6′,2″-terpyridine ligand is described together with the characterisation of an unexpected intermediate. Homoleptic complexes of the solubilised ligand 4′-(4- tert -butylphenyl)-2,2′ : 6′,2″-terpyridine, 1 , with cobalt(II), cobalt(III), ruthenium(II), iron(II) and nickel(II) have been prepared. The ligand is slightly electron releasing and solubilises the complexes in organic media.

A convenient high yield synthesis of 2,2′:6′,2″:6″,2‴:6‴,2″″ :6″″,2″‴-sexipyridine and helical transition-metal complexes of substituted sexipyridines

The compound 2,2′:6′,2″:6″,2‴:6‴,2″″:6″″,2″‴-sexipyridine (spy) has been synthesised in high yield by the coupling of 6-bromo-2,2′:6′,2″-terpyridine with a nickel(0) reagent, followed by demetallation of the resultant double-helical [Ni2(spy)2]4+ complex with KCN. In order to probe the effects of substitution of spy upon helication processes, the substituted compounds 4′,4″″-bis(methylsulfanyl)-2,2′:6′,2″:6″,2‴:6‴,2″″:6″″,2″‴-sexipyridine (msspy), 4′,4″″-diphenyl-2,2′:6′,2″:6″,2‴:6‴,2″″:6″″,2″‴-sexipyridine (pspy) and 4′,4″″-bis(4-tert-butylphenyl)-2,2′:6′,2″:6″,2‴:6‴,2″″:6″″,2″‴-sexipyridine (tbspy) were also prepared and studied. The reaction of each of these compounds with transition-metal ions capable of adopting an octahedral geometry results in the self-assembly of dinuclear double-helical complexes of the type [M2L2]4+[M = iron(II), cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) or mercury(II); L = spy, msspy, pspy or tbspy]; the double-helical topology of the zinc complex of pspy was confirmed by a crystal-structure analysis of the salt [Zn2(pspy)2][PF6]4·2MeCN·2H2O [space group P42212, a= 15.518(2), c= 18.443(1)A, R= 0.0638, R′= 0.0735].

Synthesis and coordination chemistry of 4′,4″-disubstituted 2,2′:6′,2″:6″,2‴-quaterpyridines and crystal and molecular structures of nickel(II) and cobalt(II) complexes

A range of symmetrical 4′,4″-disubstituted 2,2′:6′,2″:6″,2‴-quaterpyridines has been prepared and their coordination behaviour with metal ions having a preference for tetrahedral and octahedral geometries has been studied. The new ligands reacted with copper(I) and silver(I) salts to form dinuclear double-helical complexes; reaction with nickel(II) or cobalt(II) salts gave mononuclear species. The crystal structures of three mononuclear complexes are reported and demonstrate that the ligand binds in a tetradentate mode to the equatorial plane of the octahedral metal centre.

Cinnamil - an oligopyridine precursor

Abstract A new methodology has been employed to synthesize a quaterpyridine, a sexipyridine and a quaterpyridine analogue in which the central 2,2′-bipyridine unit is derived from cinnamil.

4′-(9-Anthryl)-2,2′:6′,2″-terpyridine—a novel luminescent component for metallosupramolecular systems

Abstract An anthryl-substituted 2,2′:6′,2″-terpyridine has been prepared, and the photochemical properties of the new ligand and its ruthenium and iron complexes studied.

4′-(4-fluorophenyl)-2,2′:6′,2″-terpyridine — an aryl-2,2′:6′,2″-terpyridine with an electron-releasing aryl substituent

A new ligand bearing a fluorophenyl substituent, 4′-(4-fluorophenyl)-2,2′:6′,2″-terpyridine (ftpy) has been prepared and an intermediate in its synthesis, 3-(4-fluorophenyl)pentane-1,5-bis(2-pyridyl)-1,5-dione (C21H17FO2N2, , α = 94.110(4)°, β = 112.016(4)°, γ = 100.537(4)°, triclinic, P, Z = 2) has been structurally characterised. Iron (II), cobalt(II) and ruthenium(II) complexes of the new ligand have been prepared and the electronic effects of the fluorophenyl substituent have been quantified. The fluorophenyl substituent is found to be electron-releasing.

Photoisomerisation of 9-anthrylsubstituted pyridyl enones

Abstract The enone 3-(9-anthryl)-1-(2-pyridyl)-2-propenone undergoes a facile photochemical E to Z isomerisation. Studies of related enones indicate that the photochemical properties are controlled by subtle changes in the structure of the molecule.

Bent aromatic rings in naphthalene derivatives

Abstract X-Ray crystallography and dynamic 1H NMR spectroscopy have revealed that 1,4,5,8-tetramethyl-, 1-bromomethyl-4,5,8-trimethyl-, and 1,8-bis(bromomethyl)-4,5-dimethyl-2,3,6,7-tetrabromonaphthalene — 3, 4, and 5, respectively — have severely distorted naphthalene nuclei in the solid state that also correspond to the gross conformations that occupy appreciable (ΔG‡∼16 kcal mol−1) energy wells in the solution state.