Two new chiral liquid crystalline monomers with bilactate or trilactate chiral units were synthesized and studied. The monomers show the paraelectric SmA and ferroelectric SmC∗ phases. The antiferroelectric phase was detected only for the monomer possessing the bilactate unit. The temperature dependences of the spontaneous polarization and spontaneous tilt angle were measured. Real and imaginary parts of the complex permittivity were studied as a function of frequency and temperature. The synthesized monomers contain a double bond at the end of the achiral terminal chain, and were used to prepare liquid crystalline polysiloxanes.
A family of homodinuclear Ln3+ (Ln3+ = Gd3+, Eu3+) luminescent complexes with the general formula [Ln2(β-diketonato)6(N-oxide)y] has been developed to study the effect of the β-diketonato and N-oxide ligands on their thermometric properties. The investigated complexes are [Ln2(tta)6(pyrzMO)2] (Ln = Eu (1·C7H8), Gd (5)), [Ln2(dbm)6(pyrzMO)2] (Ln = Eu (2), Gd (6)), [Ln2(bta)6(pyrzMO)2] (Ln = Eu (3), Gd (7)), [Ln2(hfac)6(pyrzMO)3] (Ln = Eu (4), Gd (8)) (pyrzMO = pyrazine N-oxide, Htta = thenoyltrifluoroacetone, Hdbm = dibenzoylmethane, Hbta = benzoyltrifluoroacetone, Hhfac = hexafluoroacetylacetone, C7H8 = toluene), and their 4,4′-bipyridine N-oxide (bipyMO) analogues. Europium complexes emit a bright red light under UV radiation at room temperature, whose intensity displays a strong temperature (T) dependence between 223 and 373 K. This remarkable variation is exploited to develop a series of luminescent thermometers by using the integrated intensity of the 5D0 → 7F2 europium transition as the thermometric parameter (Δ). The effect of different β-diketonato and N-oxide ligands is investigated with particular regard to the shape of thermometer calibration (Δ vs T) and relative thermal sensitivity curves: i.e.. the change in Δ per degree of temperature variation usually indicated as Sr (% K–1). The thermometric properties are determined by the presence of two nonradiative deactivation channels, back energy transfer (BEnT) from Eu3+ to the ligand triplet levels and ligand to metal charge transfer (LMCT). In the complexes bearing tta and dbm ligands, whose triplet energy is ca. 20000 cm–1, both deactivation channels are active in the same temperature range, and both contribute to determine the thermometric properties. Conversely, with bta and hfac ligands the response of the europium luminescence to temperature variation is ruled by LMCT channels since the high triplet energy (>21400 cm–1) makes BEnT ineffective in the investigated temperature range.
The syntheses of the complexes [PtCl2(NCR)L] [R = Me, Et; L = PPh3; R = Et, L = Py, CO] and [PtCl{(κ2-P,C)P(OC6H4)(OPh)2}(NCEt)] are described starting from the easily available [PtCl2(NCR)2]. The stability of the products under different experimental conditions is discussed as well as their use as precursors to dinuclear complexes [Pt(μ-Cl)ClL]2. The crystal and molecular structures of cis-[PtCl2(NCEt)(PPh3)], [SP-4-2]-[PtCl{(κ2-P,C)P(OC6H4)(OPh)2}(NCEt)] and trans-[Pt(μ-Cl){(κ2-P,C)P(OC6H4)(OPh)2}]2 are reported.