Jean-Marc Kern

A Transition Metal Containing Rotaxane in Motion: Electrochemically Induced Pirouetting of the Ring on the Threaded Dumbbell

Fast spinning motion is observed in a copper(I) rotaxane. This “motor-like” molecule consists of an axle, bearing two bulky stoppers at its ends, and a ring containing two differrent coordination sites, each of them corresponding to the preferred situation for copper(I) or copper(II). Thus, using electrochemistry, the axle can be forced to oscillate inside the wheel.

Photoassisted C–C coupling via electron transfer to benzylic halides by a bis(di-imine) copper(I) complex

Owing to its special topography Cu(dap)2+[dap = 2,9 bis(p-anisyl)-1,10-phenanthroline] displays photophysical properties which allow its use as an efficient redox photocatalyst in reductive coupling of p-NO2C6H4CH2Br.

Absorption and luminescence properties of 1, 10-phenanthroline, 2, 9-diphenyl-1, 10-phenanthroline, 2,9-dianisyl-1, 10-phenanthroline and their protonated forms in dichloromethane solution

Addition of trifluoroacetic acid to CH2Cl2 solutions of 1, 10-phenanthroline (1), 2,9-diphenyl-1, 10-phenanthroline (2) and 2,9-dianisyl-1, 10-phenanthroline (3) causes strong changes in the absorption and fluorescence spectra at room temperature. The low-energy absorption bands move to the red, while isosbestic points are maintained. The intensity of the structured, short-lived ππ* fluorescence band decreases and a new, unstructured longer-lived fluorescence band arises at longer wavelength. The number of equivalents of acid needed to obtain 50% protonation in the ground state increases in the series 3 < 2 < 1. The spectral changes can be fully reversed by addition of base. The proton affinity in the singlet excited state is higher than that in the ground state (ΔpKa≈ 14 units for 3), but the protonation and deprotonation processes are too slow to compete with the excited-state decay. In a rigid CH2Cl2 matrix at 77 K the shift of the fluorescence band upon protonation is smaller than that observed at room temperature. The effect of protonation on the phosphorescence band, which can be observed in the rigid CH2Cl2 matrix at 77 K, is very small.

Conjugated polyrotaxanes: improvement of the polymer properties by using sterically hindered coordinating units

A new conjugated copper-complexed polyrotaxane has been prepared by electropolymerization of a thiophene derivative; the rings are threaded onto a multi-1,10-phenanthroline (phen) axle, copper(I) acting as a template. The presence of CH3 groups ortho to the nitrogen atoms of the phen nuclei belonging to the conjugated backbone has a profound effect on the stability of the polymer, on its electrochemical properties and on its ability to be remetallated once the template metal centre (copper(I)) has been removed.

Multiring interlocked systems via transition metal-templated strategy: The single-cyclization synthesis of [3]-catenates

Abstract The synthesis of a potential precursor of a multi-interlocking ring system is described. This precursor consists of two lipophilic 4,7-di-(n-hexyl)-2,9-di-phenyl-1,10-phenanthroline moieties linked by a diacetylenic bridge and ended by two alkyne groups. The Cu(I)-templated double threading of this bis-chelate string into two coordinating macrocycles was demonstrated. An intramolecular cyclization (Glaser oxidation) of this preorganized system leads to the corresponding dicopper(I) [3]-catenate in 48% yield.

Nature of the lowest energy excited state of a bis-phenanthroline [2]-catenand and its Cu(I), Ag(I) and Co(II) complexes

Abstract The excited state absorption and emission spectra and lifetimes of a [2]-catenand made of two interlocked 30-membered rings (containing 2,9-dianisyl-1,10-phenanthroline-type coordinating moietes) and its Co2+, Cu+, and Ag+ complexes have been investigated in CH2Cl2 solution. The lowest energy excited state is established to be a triplet ligand-centered level for the Ag+ complex and a triplet metal-to-ligand charge-transfer level for the Cu+ complex. For the Co2+ complex, where no emission or transient absorption can be observed, the lowest excited state is most likely to be a distorted triplet metal-centered level. No transient absorption can be observed for the lowest energy triplet excited state of the [2]-catenand in CH2Cl2 solution because of a fast reaction with solvent molecules.

Absorption and emission properties of a 2-catenand, its protonated forms, and its complexes with Li+, Cu+, Ag+, Co2+, Ni2+, Zn2+, Pd2+ and Cd2+: tuning of the luminescence over the whole visible spectral region

The absorption spectra (at 298 K), luminescence spectra and lifetimes (at 77 and 298 K) and luminescence quantum yields (at 298 K) of a catenand, its mono- and diprotonated forms, and its complexes with Li+, Cu+, Ag+, Co2+, Ni2+, Zn2+, Pd2+ and Cd2+ in CH2Cl2 solutions are obtained. The catenand (L) consists of two interlocked 30-membered rings, each one containing a 2,9-diphenyl-1,10-phenanthroline-type co-ordinating moiety. Upon addition of trifluoroacetic acid to CH2Cl2 solutions of L, significant changes in the absorption and luminescence properties are observed, that are fully reversed on addition of base. Comparison with the behaviour of a reference compound, 2,9-di(p-methoxyphenyl)-1,10-phenanthroline suggests that the catenand protonation does not occur at each phenanthroline-type moiety, but involves co-ordination of both moieties around one or two protons (in HL+ or H2L2+ respectively). The free catenand shows 1(ππ*) fluorescence (λmax= 400 nm, τ= 2.0 ns, Φ= 0.42) at 298 K, and both 1(ππ*) fluorescence (λmax= 382 nm, τ= 2.2 ns) and 3(ππ*) phosphorescence (λmax= 524 nm, τ= 0.79 s) in a rigid matrix at 77 K. The metal complexes of L are forced to have a tetrahedral-type co-ordination geometry because of the entwined arrangement of the two phenanthroline ligands. The only exception is for the Pd2+ complex in which orthometallation is observed to avoid a tetrahedral co-ordination. The complexes with Li+, Cd2+ and Zn2+ exhibit ligand-centred (l.c.) fluorescence and phosphorescence, this being considerably more perturbed from that of L for the divalent ions. The complexes of Co2+ and Ni2+ are not luminescent, as expected because of the presence of low energy metal-centred levels which offer a pathway to a fast radiationless decay of the l.c. levels. The copper(I) complex exhibits an emission band in the red spectral region (298 K: λmax= 730 nm, τ= 175 ns, Φ= 0.0011; 77 K: λmax= 690 nm, τ= 1.1 µs), that can be assigned to the lowest energy triplet metal-to-ligand charge transfer (m.l.c.t.) excited state. For the silver(I) complex no emission can be observed at room temperature, whereas in a rigid matrix at 77 K a very intense, long-lived band is present at about 498 nm (τ= 0.012 s) that can be assigned to the lowest 3l.c. level. The palladium(II) complex, in which the first co-ordination sphere of the metal ion is constituted by C–-phenyl and two phenanthroline nitrogens of a diphenylphenanthroline unit and a nitrogen of the other diphenylphenanthroline unit, displays an emission band at 555 nm (τ= 3.0 × 10–4 s) at 77 K that can be assigned to a perturbed 3m.l.c.t. level. The emission maxima of L, HL+ and H2L2+ and its six luminescent metal complexes cover the range 378–730 nm, showing that it is possible to tune the luminescence of the L derivatives over the whole visible spectral region.

Tangled 3-functionalized polypyrrole derivatives built around Cu(dpp)2+ (dpp = 2,9-diphenyl-1,10-phenanthroline)

Abstract The 2,9-bis[ p -(8-(pyrrol-3-yl)-octan-1-oxy)phenyl]-1,10-phenanthroline ligand L was synthesized by condensation of 2,9 di( p -hydroxyphenyl)-1,10-phenanthroline with the mesylate derivative of 1-(triisopropylsilyl)-3-(1-octan-8-ol)-pyrrole in dimethylformamide+K 2 CO 3 medium followed by N-deprotection using CsF. The entwined complex of Cu + (CuL 2 ) + is characterized by NMR and cyclic voltammetry. Electropolymerization of this complex generates a film. The electrode modified in this way exhibits electroactivity of both the copper complex ( E Cu II /cu I= 0.4 V; E Cu I /Cu o= 1.6 V) and the polypyrrolic matrix (3-PPy) ( E 3PPy = -0.4 V vs. Ag/10 −2 mol 1 −1 Ag + ). Compared with the N -pyrrole ( E N -PPy = E Cu II /Cu I) and 3-thiophene ( E 3-PT > E Cu II /Cu I) substituted series, the relative location of the potential values ( E 3-PPY E Cu II /Cu I) is the most favourable for the electrical wiring of the Cu II /Cu I couple. The doping level of the poly(Cu(L) 2 ) + film is 0.2.

Conjugated polyrotaxanes containing coordinating units: reversible copper(I) metallation–demetallation using lithium as intermediate scaffolding

A new polyrotaxane containing a conjugated backbone has been synthesized via a copper(I) template and electropolymerisation; after decomplexation of CuI, remetallation is only possible if lithium is present during copper removal, as labile scaffolding able to prevent collapse of the free coordination sites and of the organic matrix.

Protonation of free 2,9-bis(p-biphenylyl)-1,10-phenanthrolinesites in a 56-membered macrocycle and in its ReIand CuIcomplexes Absorption spectra, luminescence properties, and excited state interactions

We have investigated the absorption and luminescence properties, and the 1H NMR spectra of (i) a macrocycle (L–L) made of a 56-membered ring incorporating two 2,9-bis(p-biphenylyl)-1,10-phenanthroline units and (ii) its metal complexes (L–L)Re(CO)3Cl and [(L–L)Cu(A)]+, where the latter is a catenate species (A is a 33-membered macrocycle containing a 2,9-p-biphenylyl-1,10-phenanthroline unit). The free macrocycle and its complexes contain, respectively, two and one free phenanthroline sites which can be protonated. Addition of trifluoroacetic acid to CH2Cl2 solutions of L–L, (L–L)Re(CO)3Cl, and [(L–L)Cu(A)]+ causes strong changes in the absorption spectra, with maintenance of the same family of isosbestic points in all cases. The 1H NMR spectrum of L–L is identical to that of the uncomplexed phenanthroline site of [(L–L)Cu(A)]+ and (L–L)Re(CO)3Cl. Such absorption and NMR data show that the two phenanthroline units of L–L do not interact in the ground state. For this macrocycle, the changes in the absorption spectrum upon protonation are accompanied by the disappearance of the very strong (emission quantum yield Φem = 0.89), short lived (τ = 1.7 ns) fluorescence band (λmax = 419 nm) of the 2,9-bis(p-biphenylyl)-1,10-phenanthroline units, with the appearance of a weak (Φem = 0.019), short lived (τ = 1.9 ns), strongly red-shifted (λmax = 572 nm) band. The results obtained show that the two equivalent basic sites of L–L are independently protonated. In the monoprotonated L · H+–L species, energy transfer from the unprotonated to the protonated site occurs. The phosphorescence band of L–L (λmax = 538 nm, τ = 0.8 s), which can be observed on cooling the solution to 77 K, moves slightly to the red (λmax = 571 nm, τ = 1.1 s) upon protonation. In the [(L–L)Cu(A)]+ and (L–L)Re(CO)3Cl complexes, protonation occurs at the free coordination site, as shown by the changes observed in the absorption and emission spectra. In the [(L · H+–L)Cu(A)]+ complex, the lowest triplet metal-to-ligand charge-transfer (3MLCT) level of the metal-based moiety lies below the lowest singlet excited state and the lowest triplet excited state of the protonated moiety. Therefore, both the fluorescence and (at 77 K) the phosphorescence of the protonated moiety are, at least in part, quenched. In Re(L · H+–L)(CO)3Cl, the lowest 3MLCT of the Re-based moiety is very close in energy to the fluorescent and phosphorescent levels of the protonated moiety with a consequent more complex luminescence behaviour.