Saddle-Shaped Cyclic Indole Tetramers: 3D Electroactive Molecules

π-Extended Octupolar Cyclized Indole Tetramer and Trimer Derivatives with Second- and Third-Order Nonlinear Optical Properties

Several aromatic-fused octupolar tetraindole (TTI) and triindole (TI) derivatives have been synthesized via POCl₃-promoted cyclopolymerization of the aromatic-fused oxindoles. As a result, the terminal phenyls of TTI and TI are fused with the phenyl group, indenyl group, and benzothienyl group separately in the π-extended target compounds TTIp and TIp, TTIid and TIid, and TTIbt and TIbt (including pairs of syn- and anti-isomers). Single-crystal X-ray diffraction disclosed that the tetramer syn-TTIbt keeps an S₄-symmetric architecture and crystallizes in the P4₂/n space group. With the extension of the π-conjugation, the absorption and emission bands of the above tetramers and trimers are remarkably red-shifted. The second-order nonlinear optical (NLO) coefficients (β value) of syn-TTIbt and anti-TTIbt have been calculated to be 1.5 and 2.1 times that of their parent compound TTI, respectively. In the domain of the third-order NLO, the two-photon absorption sections (δ value) of syn-TIbt and anti-TIbt have been measured to be 37 and 102 times that of TI, respectively. These results indicate that the π-extension strategy here is successful, and the anti-isomers have better NLO properties and better π-conjugation than their corresponding syn-isomers.

Shape-assisted self-assembly

Self-assembly and molecular recognition are critical processes both in life and material sciences. They usually depend on strong, directional non-covalent interactions to gain specificity and to make long-range organization possible. Most supramolecular constructs are also at least partially governed by topography, whose role is hard to disentangle. This makes it nearly impossible to discern the potential of shape and motion in the creation of complexity. Here, we demonstrate that long-range order in supramolecular constructs can be assisted by the topography of the individual units even in the absence of highly directional interactions. Molecular units of remarkable simplicity self-assemble in solution to give single-molecule thin two-dimensional supramolecular polymers of defined boundaries. This dramatic example spotlights the critical function that topography can have in molecular assembly and paves the path to rationally designed systems of increasing sophistication.

Self-assembly and molecular recognition usually depend on strong, directional non-covalent interactions but also topography can play a role in the formation of supramolecular constructs which makes it nearly impossible to discern the potential of shape and motion in the creation of complexity. Here, the authors demonstrate that long-range order in supramolecular constructs can be assisted by the topography of the individual units even in the absence of highly directional interactions.

Palladium(ii) catalysed cascade strategy for the synthesis of dibenzo[5,6:7,8]cycloocta[1,2-b]indol-10-ols/-10(15H)-ones: easy access to 1,3,5,7-cyclooctatetraenes (COTs)

An atom-economic Pd(ii)-catalysed cascade cyclisation of 2-(biphenylethynyl)anilines tethered to an aldehyde or cyano group leads to the formation of dibenzo[5,6:7,8]cycloocta[1,2-b]indol-10-ols 6 or dibenzo[5,6:7,8]cycloocta[1,2-b]indol-10(15H)-ones 8 with high yields (up to 95%). The reaction proceeds via amino-palladation of the alkyne followed by nucleophilic addition onto the aldehyde/cyano group. Treatment of 6 with p-TsOH·H₂O smoothly provided cyclooctatetraene (COT) derivatives 7.