In supramolecular systems, the interaction between different units modulates their photophysical properties. a) For platinum(II) complexes with ligands that have extended π systems, π-stacking and direct metal-metal interactions result in the formation of excimers with characteristically red-shifted luminescence. Time-resolved emission spectra show clear evidence of dual luminescence. b) In phthalocyanines to which electron-donating tetrathiafulvalene (TTF) groups have been fused, the luminescence is strongly quenched by intramolecular electron transfer. The luminescence can be switched on by oxidation of the TTF groups. c) The luminescence of ruthenium tris-bipyridyl derivatives is strongly influenced by the environment. Linked to biotin, the luminescence quantum yield of such a complex is enhanced by 30 % upon binding to avidin. Furthermore, the binding to avidin induces a circular-dichroism signal from the π-π* transition of the initially racemic ruthenium tris-bipyridyl derivative.

Inert and optically active pseudo-octahedral Cr^IIIN₆ and Ru^IIN₆ chromophores have been incorporated by self-assembly into heterobimetallic triple-stranded helicates HHH-[CrLnL₃]⁶⁺ and HHH-[RuLnL₃]⁵⁺. The crystal structures of [CrLnL₃](CF₃SO₃)₆ (Ln=Nd, Eu, Yb, Lu) and [RuLnL₃](CF₃SO₃)₅ (Ln=Eu, Lu) demonstrate that the helical structure can accommodate metal ions of different sizes, without sizeable change in the intermetallic M^…Ln distances. These systems are ideally suited for unravelling the molecular factors affecting the intermetallic nd→4f communication. Visible irradiation of the Cr^IIIN₆ and Ru^IIN₆ chromophores in HHH-[MLnL₃]^5/6+ (Ln=Nd, Yb, Er; M=Cr, Ru) eventually produces lanthanide-based near infrared (NIR) emission, after directional energy migration within the complexes. Depending on the kinetic regime associated with each specific d-f pair, the NIR luminescence decay times can be tuned from micro- to milliseconds. The origin of this effect, together with its rational control for programming optical functions in discrete heterobimetallic entities, are discussed.

Unsymmetrical substituted bidentate benzimidazol-2-ylpyridine ligands L2 and L3 react with [Ru(dmso)₄Cl₂] in ethanol to give statistical 1:3 mixtures of fac-[Ru(Li)₃]²⁺ and mer-[Ru(Li)₃]²⁺ (i=2, 3; ΔGΘ_{isomerisation}=-2.7 kJ mol^-1). In more polar solvents (acetonitrile, methanol), the free energy of the facial ↔ meridional isomerisation process favours mer-[Ru(Li)₃]²⁺, which is the only isomer observed in solution at the equilibrium (ΔGΘ_{isomerisation}≤-11.4 kJ mol^-1). Since the latter process takes several days for [Ru(L2)₃]²⁺, fac-[Ru(L2)₃]²⁺ and mer-[Ru(L2)₃]²⁺ have been separated by chromatography, but the 28-fold increase in velocity observed for [Ru(L3)₃]²⁺ provides only mer-[Ru(L3)₃](ClO₄)₂ after chromatography (RuC₆₀H₅₁N₉O₈Cl₂, monoclinic, P2₁/n, Z=4). The facial isomer can be stabilised when an appended tridentate binding unit, connected at the 5-position of the benzimidazol-2-ylpyridine unit in ligand L1, interacts with nine-coordinate lanthanides(III). The free energy of the facial↔meridional isomerisation is reversed (ΔGΘ_{isomerisation}≥11.4 kJ mol^-1), and the Ru — N bonds are labile enough to allow the quantitative thermodynamic self-assembly of HHH-[RuLu(L1)₃]⁵⁺ within hours ([RuLu(L1)₃](CF₃SO₃)_4.5Cl_0.5(CH₃OH)_2.5: RuLuC₁₀₆H₁₀₉Cl_0.5N₂₁O₁₉S_4.5F_13.5, triclinic, P, Z=2). Electrochemical and photophysical studies show that the benzimidazol-2-ylpyridine units in L1-L3 display similar Ï€-acceptor properties to, but stronger Ï€-donor properties than, those found in 2,2'-bipyridine. This shifts the intraligand π→π^* and the MLCT transitions toward lower energies in the pseudo-octahedral [Ru(Li)₃]²⁺ (i=2, 3) chromophores. The concomitant short lifetime of the ³MLCT excited state points to efficient, thermally activated quenching via low-energy Ru-centred d-d states, a limitation which is partially overcome by mechanical coupling in HHH-[RuLu(L1)₃]⁵⁺.

A novel ruthenium complex with a 6,7-dicyanosubstituted dppz ligand has been synthesised: its crystal structure and physico-chemical studies are reported.

The physical and photophysical properties of three classic transition metal complexes, namely [Fe(bpy)₃]²⁺, [Ru(bpy)₃]²⁺, and [Co(bpy)₃]²⁺, can be tuned by doping them into a variety of inert crystalline host lattices. The underlying guest-host interactions are discussed in terms of a chemical pressure.