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International audience; This work introduces 2,2′-bipyrimidine as an acceptor unit in the design of donor−acceptor conjugated polymers. Regularly alternating this moiety with the electron-rich 2,7-dihexyl fluorene and 3,6-carbazole units lead to polymers P1 and P2, respectively, which both showed a red-shifted emission with respect to the parent polyfluorene and polycarbazole derivatives. Investigations on the thermal properties showed that P1 and P2 both possess decomposition temperatures higher than 250°C under a mixture of N 2 and O 2. P1 was used as a representative example of this family of conjugated polymers to design white-emitting materials, both in solution and in the solid state. P1 and P2 were investigated as phosphors for LED lighting. Two composite films elaborated with P1 and P2 embedded into a PMMA matrix labeled P1c and P2c, respectively, were irradiated with a 375 nm-LED at a power as high as 48 W/m 2. P1c was found to show a lower photostability. Two ways to improve the stability under UV exposure were investigated. On the one hand, replacing 2,7-dihexyl fluorene by 3,6-hexyl carbazole approximately improved the photostability by a factor of 2, while on the other hand, embedding the polymers into a liquid sol−gel hybrid matrix allowed an improvement of the stability by a factor of 3. We could obtain a stabilization of the intensity of P2c at ∼half of its initial intensity, thus showing an improvement of the photostability of more than five times with respect to pure P1.

Six polyfluorene derivatives, P1–P6, were synthesized and investigated as responsive materials for the optical sensing of metal ions in an aqueous medium. They were designed by combining carbazole with fluorene units within the backbone. Carbazole was N-functionalized with three coordinating groups, 2-pyridyl-benzimidazole (P1 and P4), 2-phenyl-benzimidazole (P2 and P5) and 4-phenyl-terpyridyl (P3 and P6), respectively. P1–P3 are random copolymers with fluorene:carbazole ratios of 9:1 for P1 and P2, and 9.7:0.3 for P3; P4–P6 are the corresponding alternating polymers. This design lead to polymers made of a conjugated backbone and pendant coordinating groups. The optical properties of the monomers were impacted in various ways by metal ions, and the formation of the [NiM3]2+ and [ZnM3]2+ and [ZnM32]2+ were evidenced with association constants of 105.22, 106.45 and 1014.0, respectively. The emission of the polymers was afterwards found to be influenced by theses metal ions with different sensitivity and selectivity. P1 was found to be more sensitive to the Ni2+ and Cu2+ ions with a better selectivity for Ni2+. Emission of the corresponding alternating polymer P4 was more efficiently quenched by these two ions with respect to P1, in addition of being sensitive to the Ca2+ and Al3+ ions. P3 showed sensitivity to the Ni2+, Cu2+, Al3+, Ca2+, and Zn2+ ions. The luminescence of P6 was much more pronounced with the Ni2+, Cu2+, Cd2+, Zn2+, Al3+, Fe2+, and Fe3+ ions with respect to P3. More remarkably, the presence of the Zn2+ or Cd2+ ions resulted in a new emission band, leading to the possibility to selectively sense these two ions. Relatively high Stern-Volmer constants (in the 106–105 range) were obtained, and sensitivities down to the ppb level were reached, especially for the Ni2+ ion. Influence of both the coordinating group and the polymer backbone on the polymers sensitivity and selectivity was emphasized. Finally, the recyclability of some representative optical sensors was shown both in solution and in the solid state. In particular, thin films were shown to be easily regenerated, which opens the way to the elaboration of reusable optical sensors.

The strategy of stereodivergent reactions on racemic mixtures (stereodivergent RRM) was employed for the first time in intramolecular benzoin reactions and led to the rapid access of chromanones/flavanones with two consecutive stereocenters. The easily separable stereoisomers of the products were obtained with moderate to excellent enantioselectivities in a single step. Catechol type additives proved crucial in achieving the desired diastereo- and enantioselectivities.

The efficient, highly enantioselective preparation of a variety of tetralone derivatives with two contiguous stereocenters and diverse functional groups is described.

The asymmetric desymmetrization of 1,4-dienes via chiral N-heterocyclic carbene catalyzed Stetter-type umpolung reaction was demonstrated. A variety of differently substituted dienes were tolerated very well, affording cyclic ketones with two consecutive stereogenic centers (including one quaternary carbon) in moderate to high yields and with high to excellent enantioselectivities. This work expanded both reaction types of catalytic diene desymmetrizations and substrate diversity in NHC catalyzed desymmetric transformations.

A general method for the asymmetric desymmetrization of 1,3-diketone substrates via chiral N-heterocyclic carbene catalyzed intramolecular benzoin reactions was developed. Five- and six-membered cyclic ketones bearing two contiguous fully substituted stereocenters were generated with excellent diastereoselectivities and moderate to excellent enantioselectivities.

The highly enantio-, diastereo-, and regioselective dynamic kinetic resolution of β-ketoesters and 1,3-diketones was achieved via a chiral N-heterocyclic carbene catalyzed intramolecular cross-benzoin reaction. A variety of tetralone derivatives bearing two contiguous stereocenters and multiple functionalities were liberated in moderate to excellent yields and with high levels of stereoselectivity (95% ee and20:1 dr in most cases). In addition, the excellent regioselectivity control for aryl/alkyl 1,3-diketones, and the superior electronic differentiation of 1,3-diarylketones were highlighted. Moreover, a set of new mechanistic rationale that differs with the currently widely accepted understanding of intramolecular benzoin reactions was established to demonstrate the superior preference of benzoin over aldol transformation: (1) A coexistence of competitive aldol and benzoin reactions was detected, but a retro-aldol-irreversible benzoin process performs a vital role in the generation of predominant benzoin products. (2) The most essential role of an N-electron-withdrawing substituent in triazolium catalysts was revealed to be accelerating the rate of the benzoin transformation, rather than suppressing the aldol process through reducing the inherent basicity of the catalyst.

The asymmetric desymmetrization of 1,4-dienes via chiral N-heterocyclic carbene catalyzed Stetter-type umpolung reaction was demonstrated. A variety of differently substituted dienes were tolerated very well, affording cyclic ketones with two consecutive stereogenic centers (including one quaternary carbon) in moderate to high yields and with high to excellent enantioselectivities. This work expanded both reaction types of catalytic diene desymmetrizations and substrate diversity in NHC catalyzed desymmetric transformations.

A general method for the asymmetric desymmetrization of 1,3-diketone substrates via chiral N-heterocyclic carbene catalyzed intramolecular benzoin reactions was developed. Five- and six-membered cyclic ketones bearing two contiguous fully substituted stereocenters were generated with excellent diastereoselectivities and moderate to excellent enantioselectivities.