Unprecedented Demonstration of Regioselective SE Ar Reaction giving Unsymmetrical Regioregular Oligothiophenes.

Aromatization of 4-cyano-3-oxotetrahydrothiophene by sulfuryl chloride gives the new building block 4-cyano-3-pyrrolidylthiophene, which forms unsymmetrical regioregular oligothiophenes with a strict alternation of the donor and acceptor groups along the conjugated system. The self-coupling reactions that form the oligomers are shown to proceed by a regioselective electrophilic aromatic substitution mechanism involving a stabilized Wheland intermediate.

Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives.

A series of 2,5-distyrylfuran derivatives bearing pentafluorophenyl- and cyanovinyl units have been synthesized for aggregation-induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X-ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single-crystal X-ray diffraction analysis confirmed that CH⋅⋅⋅F, F⋅⋅⋅F, CH⋅⋅⋅nitrile, Ar⋅⋅⋅ArF (Ar=aryl, ArF =fluoroaryl), and nitrile⋅⋅⋅ArF intra- and intermolecular interactions drive the topology of the molecule and that solid-state supramolecular contacts favor AIE of the furan derivatives.

Unusually high fluorescence quantum yield of a homopolyfluorenylazomethine--towards a universal fluorophore.

The absolute fluorescence quantum yield (Φfl) of a polyfluorenyl azomethine homopolymer was measured as a function of solvent polarity. The solvent induced and temperature dependent fluorescence of the homopolymer were also investigated and they were compared to the corresponding monomer and copolymer. The Φfl of the homopolymer was consistent (45-70%), regardless of solvent polarity with Stokes shifts up to 7460 cm(-1) in ethanol. In contrast, the Φfl of its corresponding monomer decreased from 60% in ethanol to 1% in toluene, whereas a Φfl < 5% for its analogous copolymer was measured. Moderate fluorescence yields (Φfl ≈ 25%) were also possible in thin film when co-depositing the homopolymer with PMMA. Cryofluorescence was used to probe the excited state deactivation modes. Deactivation by internal conversion was found to compete with fluorescence. The fluorescence deactivation pathways of the homopolymer and its corresponding monomer could be suppressed at 77 K, resulting in fluorescence turn-on. Both fluorophores were found to detect nitroaromatics.

Insight into the isoelectronic character of azomethines and vinylenes using representative models: a spectroscopic and electrochemical study.

A series of azomethine and vinylene dyad and triad analogues were prepared. Their absorbance, fluorescence, and redox properties were examined experimentally and theoretically using density functional theory (DFT) calculations. These measurements were done to determine the effect of the heteroatom of the azomethine relative to its all-carbon counterpart and to assess the isoelectronic character of the two bonds. The orientation of the azomethine was found to have little effect on the absorbance, fluorescence, and electrochemical properties. In contrast, the spectral and electrochemical properties were highly contingent on the electronic groups and degree of conjugation. The spectral properties could be tuned 200 nm across the visible region. More importantly, the heteroatom in the conjugated bond was found to give rise to only a 20 nm bathochromic shift in the absorbance and fluorescence spectra. The fluorescence quantum yield (ΦFl) of the vinylene derivatives varied between 5% and 20% with fluorescence quenching occurring by photoisomerization from the E to Z isomers. In contrast, the fluorescence of the analogous azomethine derivatives was completely quenched. The collective spectroscopic and electrochemical ab initio DFT data additionally confirmed that the azomethine and its analogous vinylene are isoelectronic. It was also found that a conjugated thiophene vinylene dyad with primary amines in the α,α'-positions could be prepared and isolated. The compound was stable under aerobic conditions providing electron withdrawing (either ester or nitrile) groups were located in the adjacent positions.

Synthesis and electronic properties of D-A-D triads based on 3-alkoxy-4-cyanothiophene and benzothienothiophene blocks.

3-Alkoxy-4-cyanothiophene units are used as building block for the synthesis of conjugated donor-acceptor-donor (D-A-D) triads. The donor part consists of benzothienothiophene end groups associated with the alkoxy groups of the 3-alkoxy-4-cyanothiophene, while the central acceptor part is formed by combining the electron-withdrawing cyano group with thiophene or benzothiadiazole units.

Facile synthesis of 3-alkoxy-4-cyanothiophenes as new building blocks for donor-acceptor conjugated systems.

3-Alkoxy-4-cyanothiophenes are efficiently synthesized in two steps from the readily available 4-cyano-3-oxotetrahydrothiophene. Regioisomers of bithiophene derivatives are easily synthesized by playing on the strong electronic dissymmetry of the thiophene ring induced by the alkoxy and cyano groups.