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Synthesis of Discrete Conjugated Fluorene‐Azo Oligomers for the Investigation of Azobenzene Position‐Dependent Physical Properties and Photoresponsive Behavior
Author(s) -
Liu Min,
Shi Xianheng,
Li Lishan,
Zhang Jiandong,
Huang Zhihao,
Zhang Wei,
Zhou Nianchen,
Zhang Zhengbiao,
Zhu Xiulin
Publication year - 2021
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.202100092
Subject(s) - azobenzene , fluorene , conjugated system , polymer , solvatochromism , materials science , photochemistry , photodegradation , polymer chemistry , sequence (biology) , macromolecule , side chain , oligomer , chemistry , molecule , organic chemistry , photocatalysis , biochemistry , catalysis
Abstract It is well known that macromolecular structure, including composition, topology and sequence, significantly determines the properties of conjugated polymers/oligomers. To accurately understand the structure‐induced properties, discrete oligomers/polymers with molecularly defined structures are the ideal model because they provide distinct nonstatistical results. Herein, a series of discrete conjugated fluorene‐azo oligomers with different positions of the azobenzene units along the main chain (i.e., sequence) are efficiently prepared based on CuAAC “click” chemistry via a stepwise chain‐growth strategy. Position‐dependent behavior has an evident impact on the properties of oligomers, such as thermal properties, optical properties and photoresponsive behavior in both solution and thin film states. In addition, the fluorene‐azo oligomers show less photodegradation of 9,9‐dioctyl‐fluorene in the solid‐state than oligofluorene during UV light irradiation; however, position‐dependent photodegradation is found in solution. Optimized configurations and UV–vis absorption spectra of fluorene‐azo oligomers are calculated by density functional theory. Experimental results and theoretical analysis indicate that the location of azobenzene can play a dominant role in determining the properties of fluorene‐azo oligomers resulting from sequence‐mandated conformational changes. Undoubtedly, this work can provide deeper insight into the structure–property relationships based on precisely sequence‐defined polymer structures.