Li Yuanchao, Nese Alper, Hu Xiangqian, Lebedeva Natalia V, LaJoie Travis W, Burdyńska Joanna, Stefan Mihaela C, You Wei, Yang Weitao, Matyjaszewski Krzysztof, Sheiko Sergei S
Department of Chemistry, University of North Carolina at Chapel Hill, North Carolina 27599, United States.
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
ACS Macro Lett. 2014 Aug 19;3(8):738-742. doi: 10.1021/mz5003323. Epub 2014 Jul 15.
Bottlebrush macromolecules can be regarded as molecular tensile machines, where tension is self-generated along the backbone due to steric repulsion between densely grafted side chains. This intrinsic tension is amplified upon adsorption of bottlebrush molecules onto a substrate and increases with grafting density, side chain length, and strength of adhesion to the substrate. To investigate the effects of tension on the electronic structure of polythiophene (PT), bottlebrush macromolecules were prepared by grafting poly(-butyl acrylate) (PBA) side chains from PT macroinitiators by atom transfer radical polymerization (ATRP). The fluorescence spectra of submonolayers of PT bottlebrushes were measured on a Langmuir-Blodgett (LB) trough with the backbone tension adjusted by controlling the side-chain length, surface pressure, and chemical composition of a substrate. The wavelength of maximum emission has initially red-shifted, followed by a blue-shift as the backbone tension increases from 0 to 2.5 nN, which agrees with DFT calculations. The red-shift is ascribed to an increase in the conjugation length due to the extension of the PT backbone at lower force regime (0-1.0 nN), while the blue-shift is attributed to deformations of bond lengths and angles in the backbone at higher force regime (1.0-2.5 nN).
刷状大分子可被视为分子拉伸机器，由于密集接枝的侧链之间的空间排斥作用，沿主链会产生自生成张力。当刷状分子吸附到基底上时，这种固有张力会被放大，并随着接枝密度、侧链长度以及与基底的粘附强度的增加而增大。为了研究张力对聚噻吩（PT）电子结构的影响，通过原子转移自由基聚合（ATRP）从PT大分子引发剂接枝聚（丙烯酸丁酯）（PBA）侧链制备了刷状大分子。在Langmuir-Blodgett（LB）槽上测量PT刷状分子亚单层的荧光光谱，通过控制侧链长度、表面压力和基底的化学成分来调节主链张力。随着主链张力从0增加到2.5 nN，最大发射波长最初发生红移，随后发生蓝移，这与密度泛函理论（DFT）计算结果一致。红移归因于在较低力区（0 - 1.0 nN）PT主链伸展导致共轭长度增加，而蓝移则归因于在较高力区（1.0 - 2.5 nN）主链中键长和键角的变形。
