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International audience; A series of five platinum (II) complexes based on 2-phenylpyrimidine ligands have been designed. Pyridine and chloride were used as auxiliary ligands. These complexes exhibit a slightly distorted square-planar geometry. The nature and position of substituent on the phenyl ring was thoroughly studied. The presence of an electron-donating substituent on the phenyl ring in the para position of the platinum atom leads to a red shift of the lowest-energy absorption band, which corresponds to the HOMO -> LUMO transition and permits to obtain phosphorescence in deoxygenated CH2Cl2 solution. All compounds are emissive in the solid state with a significant redshift for complexes bearing electron-donating substituent on the phenyl ring of phenylpyrimidine ligand.

Eighteen push–pull pyrazine fluorophores are described. Methoxy, dimethylamino, and diphenylamino groups were used as electron-donating groups (EDGs), and six π-conjugated systems consisting of multiple bonds and 1,4-phenylene moieties were used to connect the EDGs to the pyrazine core. The chromophores were obtained by Knoevenagel condensation and palladium-catalyzed cross-coupling reactions starting from commercially available 2-methyl- or 2-chloropyrazine. The optical absorption and emission properties of these chromophores were studied in different solvents. Some proved to be highly emissive and exhibit strong emission solvatochromism, which suggests a highly polar emitting state, characteristic of compounds that undergo intramolecular charge transfer (ICT). The influences of the various electron-donating groups and π-conjugated systems on the emission and ICT have been carefully studied.

Various novel dipolar V-shaped chromophores are prepared via condensation of methylenepyran aldehydes and methylpyrimines.

This paper presents the synthesis of a series of push–pull and quadrupolar π-conjugated structures incorporating pro-aromatic methylenepyran electron-donor groups and various electron-attracting groups. Some of the methylenepyran derivatives were oxidized by I 2 to give, after reduction by Na 2 S 2 O 3 , bismethylenepyran compounds via successive steps. The electrochemical redox properties of methylenepyrans 5 – 9 and extended bismethylenepyrans 10 , 14 , and 15 determined by cyclic voltammetry indicate the formation of redox bistable systems with high bi-stability. Oxidation of the dimers obtained from 5 to 9 was also described. All compounds are colored and slightly fluorescent (except some bismethylenepyran derivatives). Some compound second-order nonlinear optical properties were investigated, and large positive values of μβ were obtained. A positive dimer effect was also observed for bispyran derivatives.

Condensation of donor-substituted aldehydes on methylpyrimidine led to two series of fluorescent molecules depending on the position of the methyl group. Whereas highly emissive 4-arylvinylpyrimidine derivatives are well-known, this is the first example of fluorescent 2-arylvinylpyrimidine compounds. The optical properties of the two families have been thoroughly compared. Whereas the series derived from 2-methylpyrimidine exhibit a blue shift in absorption and emission in comparison with 4-arylvinylpyrimidine, the influence of the position is less predictable on the fluorescence quantum yield. These compounds also exhibit halochromism: when adding acid, a bathotromic shift is observed in absorption whereas an increase of the fluorescence intensity which is red-shifted except for amino derivatives (a progressive quench of emission is observed in these cases). An emission solvatochromism study has shown that a higher intramolecular charge transfer seems to occur in 2-arylvinylpyrimidines than in 4-arylvinylpyrimidines.

The cover picture shows the crystal structure of the cationic organometallic κ-conjugated push–pull chromophore combining the mixed sandwich acceptor group [CpFe(η6-p-MeC6H4)]+, associated with the 2-tert-butyl-4H-chromen-4-ylidene donor through the asymmetric hydrazone spacer –NH–N=CH–. This dipolar chromophore exhibits solvatochromic properties, low-lying intramolecular charge-transfer transition and enhanced second-order NLO properties (μβ), as measured with the EFISH technique at 1.907 μm. The scientific cooperation between researchers from the Southern Hemisphere (Chile) and the Northern Hemisphere (France) is symbolised not only by the Southern Cross but also by the NaCl crystals of the salt desert El Salar de Atacama. Details are discussed in the article by C. Manzur, D. Carrillo, B. Caro, J.-R. Hamon et al. on p. 1131 ff.