Regulation of tectonic sequences in chain-folding-directed monodisperse isomeric oligomers precisely tailored by Ugi-hydrosilylation orthogonal cycles

Abstract

Monodisperse discrete oligomers with a tailored sequence of linkages within their backbones, which has been defined as a tectonic sequence, were precisely constructed through Ugi four-component reactions (Ugi-4CRs) coupled to hydrosilylation orthogonal cycles. Seven isomeric oligomers with the only difference in their tectonic structures being precisely placed meta- and para-isomeric linkages, referred to as 3-(dimethylsilyl)aniline (3DA) and 4-(dimethylsilyl)-aniline (4DA) with different bond-angles, were fabricated. Here, the seven monodisperse isomers had the same molecular weight (MW = 2907.31 Da), which showed a perfect fit to the theoretical value confirmed by MALDI-TOF-MS. The impact of the tectonic sequence on the properties of isomeric oligomers was verified through experimental measurements and molecular dynamic (MD) simulations. It clearly demonstrated the changes in the glass transition temperature (T_g) and the radius of gyration (R_g) due to the difference of the linkage sequence, which resulted in the different folding ways of the molecular chains. Comparing with a conventional monomer sequence or stereo sequence, this study explores a novel tectonic sequence of isomeric oligomers composed of isomeric linkage units with different bond angles, which will offer a model to increase the comprehension of how a molecular chain's 3D structure is formed driven by chain folding.