Exploring the Electronic Properties of Extended Benzofuran‐Cyanovinyl Derivatives Obtained from Lignocellulosic and Carbohydrate Platforms Raw Materials

Abstract

Two series of linear extended benzofuran derivatives associating cyanovinyl unit and phenyl or furan moieties obtained from benzaldehyde-lignocellulosic (Be series) or furaldehyde-saccharide (Fu series) platforms were prepared in order to investigate their emission and electrochemical properties. For the fluorescence in solution and solid states, contrasting results between the two series were demonstrated. For Be series a net aggregation induced emission effect was observed with high fluorescence quantum yield for the solid state. A [2 + 2] cycloaddition under irradiation at 350 nm was also revealed for one derivative of Be series. In contrast, for Fu series the fluorescence in solution is higher than in the solid state. The X-ray crystallography studies for the compounds reveal the formation of strong π-π stacking for the derivatives without emissive property in the solid state and the presence of essentially lateral contacts for emissive compounds. Taking advantage of the propensity to develop 2D π-stacking mode for the more extended derivative with a central furan cycle, organic field effect transistors presenting hole mobility have been made.

Dual-state emissionversusno emission by manipulating the molecular structures of cyanovinyl–benzofuran derivatives

“…BPF1α and BPF2α derivatives with the cyano group at the α position were obtained by the condensation of 2-benzofuran-acetonitrile 3 (ref. 33) with pentafluorophenyl–benzaldehyde 4 or 4-bromo-tetrafluoro-benzaldehyde 5 . The last compound was synthesized by the nucleophilic aromatic substitution of the fluorine atom with the bromine atom by treatment at 80 °C of pentafluorobenzaldehyde with sodium bromine in dimethyl sulfoxide.…”

“…Benzofuran acetonitrile 3 (ref. 33) and 4-bromo-2,3,5,6-tetrafluorobenzaldehyde 5 (ref. 36) were synthesized as described.…”

“…Nevertheless, for some CS compounds, in particular for dicyanodistyrylbenzenes, medium to high luminescence has been observed in solution. 33,[38][39][40][41][42] For some bright molecules in solution, the extension of the conjugation or a donor-acceptor charge transfer is claimed to explain partial rigidification of the molecule allowing the intramolecular motions to be limited; 38,39 however, there are some examples for which it is difficult to consider the rigidification of the conjugated system for justifying the suppression of the nonradiative decay. 40,41 Recently, J. Gierschner et al showed for dicyanodistyrylbenzene derivatives, bearing alkoxy groups on the external or central phenyl groups with cyano groups either in the inner (-α) or outer (-β) position of the vinylene units, that only the β-derivatives have high emission in chloroform solution.…”

“…Though these compounds present π-stacking in the crystalline solids, they present always high luminescence properties in the solid state with Φ solid superior at 50%, thus conferring a DSE effect for these derivatives. For cyanovinyl–benzofuran systems such as BF1 , 31 BF2α and β 31 and BF3 , 33 a low emission in solution and an enhancement of the emission in the solid state are achieved, i.e. the SLE effect classically observed for cyanodiarylethene derivatives.…”

“…the SLE effect classically observed for cyanodiarylethene derivatives. 34,35 However, for compound BF4 with a push-pull structure built from the electron acceptor 2-cyano furan unit and the electron donor benzofuran motif, 33 the opposite is observed, with the latter being more strongly emissive in solution. Rigidification of the conjugated systems via the donor-acceptor interaction can explain the luminescence in solution, while many π-π interactions in the solid state can be responsible for the nonradiative pathways.…”