This manuscript consists of two parts which focus on enhancing control over the polymerization of conjugated polymers. In the first part, the controlled chain-growth character of the polymerization of poly(selenophene) using Pd(Ruphos) as a catalyst system is demonstrated. Next, all-conjugated thiophene−fluorene−selenophene triblock-copolymers are synthesized in all possible orders using this catalyst. Subsequent, the properties of these advanced structures are assessed using GPC chromatography and 1 H NMR, UV−vis, and fluorescence measurements. DFT calculations were performed to explain the unusual independence of the monomer sequence during the polymerization, traditionally observed in other chain-growth protocols for conjugated polymers. ■ INTRODUCTIONπ-Conjugated polymers are well-studied materials during the last decades because of their optoelectronic properties and their potential in low-cost electronics resulting from their conductivity and easy processing. 1−10 The quest toward complex and tailored polymeric structures to improve the performance and usability was the topic of research in the recent past and continues nowadays. 11 This quest starts with obtaining as much control as possible over the polymerization mechanism, hereby turning it into a controlled chain-growth mechanism with control on end-group functionalization and molar masses. 12−15 Moreover, this enables block-copolymerization by successive monomer addition, in which the next monomer is added after the previous monomer is completely consumed. The research groups of McCullough and Yokozawa simultaneously discovered the chain-growth character of poly(3-hexylthiophene) with Ni(dppp)Cl 2 (dppp = diphenylphosphinopropane) as a catalyst. 16−19 Further research resulted also in control over other conjugated polymers that were formed in a chain-growth fashion using the same or other Ni-and Pd-based catalysts. 20−34 The controlled nature of the polymerization relies on the association of the catalyst with the π-system of the propagating polymer chain after the reductive elimination (catalyst-transfer polycondensation, CTP). 35 As a consequence, termination and transfer reactions are avoided and a controlled chain-growth polymerization mechanism is obtained. In principle, if the controlled polymerization of two different monomers is obtained under the same conditions, allconjugated block-copolymers (π-BCPs) are accessible by sequential monomer addition. Nevertheless, since the mechanism relies on the association of the catalyst with the propagating polymer, the synthetic direction is fixed from the monomer with the lowest catalyst affinity to the one with the highest catalyst affinity, as reported by the groups of Yokozawa and Wang. 30,32 As a consequence, the number of all-conjugated block-copolymers composed of electronically different blocks prepared by successive monomer addition remains scarce, e.g.

The uncatalyzed Mukaiyama aldol reaction between C,O,O-tris(trimethylsilyl)ketene acetal and aldehydes bearing alkyl, vinyl, and aromatic substituents has been studied theoretically using density functional theory with the M06-2X exchange-correlation functional. These DFT calculations mostly demonstrate that (i) the syn product is both kinetically and thermodynamically favored, (ii) the diastereoselectivity of the uncatalyzed reaction is larger than observed for the reaction catalyzed by HgI2 and it is inverted with respect to the latter, (iii) solvents with larger dielectric constants increase the activation barrier but reduce the diastereoselectivity, (iv) the concerted reaction is preferred over the stepwise reaction, and (v) the OSiMe3 group in geminal lowers the activation barrier and increases the energy of reaction. Analyzing the concerted mechanism unravels four types of cyclic transition states, two pro-anti and two pro-syn. Then, the relative energy of the most stable transition state of each type as well as of the corresponding anti and syn products shows that the syn reaction path is located at lower Gibbs enthalpy than the anti reaction path for all substituents.

Density functional theory calculations are used to reveal the relationships between the structures, energies, and NMR signatures of an octastate molecular switch composed of a dithienylethene (DTE) unit covalently linked to an indolino­[2,1-b]­oxazolidine (BOX) moiety through an ethylenic junction. Both the DTE and BOX moieties can adopt open or closed forms. The ethylenic junction can be Z or E, but the latter has been confirmed to be, by far, more stable than the former for all BOX/DTE combinations. In addition, when the DTE is open, the two thienyl units can fold to form parallel conformers, by opposition to the antiparallel or unfolded conformers. Usually parallel conformers present a higher energy than the antiparallel ones, but in the case of compound 2 having a bulky substituent (R = pPh-SMe) on the terminal thienyl group, the enthalpy of one conformer is very close (1–2 kJ mol–1) to that of the most stable antiparallel one, making photocyclization less efficient. These conformational differences and the presence of parallel DTE forms have been substantiated by analyzing experimental 1H NMR chemical shifts in light of their calculated values. These 1H NMR chemical shift calculations led to the following statements: (i) Going from state I (DTE open, BOX closed) to state II (both DTE and BOX are open) the H8 proton of compound 1 (R = Me) is deshielded by ∼0.15 ppm. (ii) The deshielding of H8 proton of compound 2 is larger and attains 0.41 ppm whereas H7 is more shielded by 0.11 ppm. (iii) Then, going from compound 1 to compound 2 leads to deshielding of both H7 and H8 protons. As a consequence, the difference of photochromism gating efficiency among compounds 1, 2, and 3 (R = pPh-OMe) can be attributed to the stabilization of parallel conformer due to an establishment of an intramolecular interaction with BOX opening.