A new family of Pt(ii) luminescent metallomesogens based on dicatenar pyridylpyrazolate ligands [Pt(pz^R(n,n)py)₂] (R(n,n) = C₆H₃(OC_nH_2n+1)₂,n= 4–18) has been prepared, and their mesomorphic and photophysical properties are described.

A series of ionic bis(pyrazole)-silver(I) and -gold(I) complexes [ML₂][A] (M = Ag, Au; A = BF₄ ⁻, PF₆ ⁻, NO₃ ⁻), prepared by coordination of the mesomorphic L = Hpz^2R(n) or non-mesomorphic L = Hpz^R(n) pyrazole ligands (Hpz^2R(n) = 3,5-bis(4-alkyloxyphenyl)pyrazole; Hpz^R(n) = 3-(4-alkyloxyphenyl)pyrazole), has been studied. The complexes exhibit enantiotropic behaviour, showing smectic A (SmA) mesophases. The choice of the ligands allows the achievement of ‘H’ or ‘U’ molecular shapes, which appear to be responsible for the attainment of liquid crystal mesophases, these not being dependent on the coordinating or non-coordinating nature of the A counteranions. The new complexes are photoluminescent both in the solid state and in solution at room temperature. In addition, the luminescent behaviour of selected compounds as a function of the temperature indicates that the luminescence is maintained in the mesophase.

Two series of novel boron difluoride adducts (BDFs), namely [BF₂(OO^R(n))] (type I) and [BF₂(OO^2R(n))] (type II) (R = C₆H₄OC_nH_{2n +1}; n = 10–18), containing β-diketonate ligands bearing 4-alkoxyphenyl substituents in position 1 or in positions 1,3 of the β-diketonate core, respectively, have been prepared. All of them display a strong interaction between the ligand and the BF₂ group, as deduced from the IR spectroscopic data, and strong blue-violet emission (λ^max _em from 400 to 440 nm), with fluorescence quantum yields from 0.69 to 0.84 (type I) and 0.48 to 0.66 (type II) and fluorescence lifetimes of 1.7 and 2.2 ns in diluted dichloromethane solution, respectively. The photophysical properties of I and II series of dyes are independent of the solvent polarity and the chain length of the alkoxyphenyl substituent(s). Moreover, they exhibit high photostability even under intense laser light. Contradicting previous interpretations, our detailed photophysical and spectroscopic study rules out excimer formation even in highly concentrated solution or in the solid state, demonstrating the resistance of these dyes to self-aggregation. All those features pave the way to the application of such fluorophores in OLEDs, solid dye lasers, chemical sensors and two-photon biological labels, to name a few.

New pyridine-functionalised pyrazole compounds [Hpz^R(n)py] (R(n) = C₆H₄OC_nH_2n+1; n = 12, 14, 16, 18; 1–4) and their corresponding silver complexes [Ag(Hpz^R(n)py)₂][A] ([A] = NO₃ ⁻, BF₄ ⁻; 5–12) have been synthesised and characterised. All of them, with the exception of 1, are liquid crystal materials exhibiting monotropic or enantiotropic SmA mesophases, in contrast to the non-mesomorphic related R(n)-monosubstituted compounds. Because the molecular shape is a factor determinant in the organisation of molecules in the liquid crystal phase, we were interested in solving the crystal structure of representative examples of the mentioned compounds, such as 1 and 6. So, the X-ray crystal structure of [Hpz^R(12)py] 1 shows the presence of dimeric units through N–H⋯N hydrogen bonds, which conform to an elongated molecular shape containing a double chain length. On the other hand, the structure of [Ag(Hpz^R(14)py)₂][NO₃] 6 also evidenced Ag–Ag bonded dimers from ‘U’-shaped cationic entities. These dimers exhibit four chains, two by two alternated, so giving rise to a longer molecular length. Of particular interest was to observe that in both structures, the dimers are layer-like packed, their lamellar structures being related to that of the mesophases found in both kinds of compounds. Furthermore, the analysis of the optical data of the compounds 2 and 4 and the silver compounds 5, 6, 9 and 10 as representative examples pointed out their luminescent behaviour as well as their good ability to act as fluorescent probes for Zn²⁺, Cu²⁺ and Ag⁺. An increase in the fluorescence quantum yields is observed in the final complexes produced in the titrations, this fact being specially notable when 9 was used as the starting compound.