2,6-薁和3,4-丙撑二氧噻吩共聚物的主链结构调控及性质研究★

doi:10.6023/A23060292

摘要/Abstract

本工作通过理性分子设计和直接芳基化聚合策略, 合成了三个基于2,6-薁和3,4-丙撑二氧噻吩的共轭聚合物P(AzProDOT-1)、P(AzProDOT-2)和P(AzProDOT-3), 其主链中薁单元偶极取向排列方式分别为无规、部分规整和高度有序. 通过密度泛函理论(density functional theory, DFT)计算、紫外-可见吸收光谱和循环伏安法等对三个聚合物的物理化学性质进行表征, 三个聚合物在溶液和薄膜状态均表现出质子响应性质. 通过溶液旋涂法构筑了三个聚合物空间电荷限制电流(space-charge-limited current, SCLC)器件, 薁单元偶极取向排列高度有序的聚合物P(AzProDOT-3)表现出最优的器件性能, 空穴和电子迁移率分别为1.41×10⁻⁴ cm²•V⁻¹•s⁻¹和1.66×10⁻⁵ cm²•V⁻¹•s⁻¹. 本工作精准调控了2,6-薁共轭聚合物的主链结构, 为薁基共轭聚合物的合成化学和明晰其结构-性质/性能关系提供了研究思路.

关键词: 2,6-薁, 3,4-丙撑二氧噻吩, 共聚物, 偶极取向, 空间电荷限制电流

Azulene has attracted significant attention for constructing novel optoelectronic materials. Tuning the dipole orientation of azulene unit in azulene-based conjugated polymers has recently aroused widespread concern and remains a great challenge due to the lack of synthetic method. Herein, we report three 2,6-azulene and 3,4-propylenedioxythiophene (ProDOT) based conjugated copolymers P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) with different dipole arrangements of azulene moieties. The regioregularity of these 2,6-azulene-ProDOT-based conjugated polymers was tuned by monomer design and direct arylation polymerization strategy, which enables a thorough study of the impact of the regioregularity on the properties of these polymers and their charge transport performance. The dipole orientation of 2,6-azulene units were regiorandom for P(AzProDOT-1), regularity with medium regioregularity for P(AzProDOT-2) and regularity with high regioregularity for P(AzProDOT-3), respectively. The number-average molecular weight values of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) estimated by gel permeation chromatography (GPC) were 11.1, 11.4 and 9.3 kDa, respectively, and the chemical structures of these three polymers were also characterized by high-temperature ¹H NMR spectra. Ultraviolet-visible (UV-vis) absorption spectra and cyclic voltammetry were conducted to evaluate the optoelectronic properties of these polymers. The blue-shift of the maximum absorption peak for P(AzProDOT-2) indicates its twisted polymer backbone and short effective π-conjugation length, while the red-shift of the maximum absorption peak for P(AzProDOT-3) demonstrates the more planar conjugated skeleton and the longer effective π-conjugation length, although its molecular weight was a little lower. Besides, there was a prominent shoulder peak in the thin film of P(AzProDOT-3) in UV-vis absorption spectrum, indicating the stronger interchain interactions in solid state. All these observations were in agreement with the density functional theory (DFT) calculation results. Due to the electron-donating property of ProDOT, these three polymers displayed strong and sensitive proton responsiveness. The ultraviolet-visible-near infrared (UV-vis-NIR) spectra of these three polymers showed obvious red-shifts (>150 nm) upon protonation, and the films of these polymers also possess strong proton responsiveness properties. Charge-carrier mobilities of these three polymers were measured by the space-charge-limited current (SCLC). The hole mobilities of thin films of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) were 1.32×10⁻⁵, 9.14×10⁻⁵ and 1.41×10⁻⁴ cm²•V⁻¹•s⁻¹, respectively, and their electron mobilities were 1.62×10⁻⁶, 7.91×10⁻⁶ and 1.66×10⁻⁵ cm²•V⁻¹•s⁻¹, respectively. The atomic force microscopy (AFM) study demonstrated that the thin film of P(AzProDOT-3) possessed the smoothest surface and the smallest root mean square (RMS) roughness, proving the optimal SCLC performance of P(AzProDOT-3) among these three polymers. Our research highlights the significant and effective strategy of rational control regioregularity of azulene-based copolymer backbone to tune physicochemical properties and molecular packing for achieving better charge transport performance. Our study also aims to give valuable insight into precision synthesis of regioregular conjugated polymers based on low-symmetric conjugated building blocks.

Key words: 2,6-azulene, 3,4-propylenedioxythiophene, copolymer, dipole orientation, space-charge-limited current

引用此文

汪洋, 向焌钧, 葛从伍, 高希珂. 2,6-薁和3,4-丙撑二氧噻吩共聚物的主链结构调控及性质研究^★[J]. 化学学报, 2023, 81(10): 1341-1349.

Yang Wang, Junjun Xiang, Congwu Ge, Xike Gao. Study on Main Chain Structure Regulation and Properties of Conjugated Copolymers Based on 2,6-Azulene and 3,4-Propylenedioxythiophene^★[J]. Acta Chimica Sinica, 2023, 81(10): 1341-1349.

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图/表 7

图1. (a) 薁的分子结构、偶极矩和质子化形式; (b) P(AzProDOT-1)、P(AzProDOT-2)和P(AzProDOT-3)的化学结构

Figure 1. Molecular structure, dipolar moment and the protonation form of azulene (a) and chemical structures of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) (b)

图式1. 聚合单体M1、M3和M4的合成路线

Scheme 1. Synthetic routes of monomers M1, M3 and M4

图式2. 聚合物P(AzProDOT-1)、P(AzProDOT-2)和P(AzProDOT-3)的合成路线

Scheme 2. Synthetic routes of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3)

Polymer	M_n^a/kDa	PDI^a	T_d^b/℃
P(AzProDOT-1)	11.1	2.29	370
P(AzProDOT-2)	11.4	2.25	374
P(AzProDOT-3)	9.3	1.46	394

表1. P(AzProDOT-1)、P(AzProDOT-2)和P(AzProDOT-3)的分子量、多分散性指数(PDI)和热分解温度

Table 1. Molecular weight, polydispersity index (PDI) and decomposition temperatures of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3)

图2. 聚合物P(AzProDOT-1)、P(AzProDOT-2)、P(AzProDOT-3)和单体M4的1H NMR图

Figure 2. 1H NMR of polymers P(AzProDOT-1), P(AzProDOT-2), P(AzProDOT-3) and monomer M4

图3. (a) P(AzProDOT-1)、P(AzProDOT-2)和P(AzProDOT-3)在氯仿溶液中的紫外-可见吸收光谱; (b) P(AzProDOT-1)、P(AzProDOT-2)和P(AzProDOT-3)在薄膜中的紫外-可见吸收光谱

Figure 3. (a) UV-vis absorption spectra of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) in chloroform solution; (b) UV-vis absorption spectra of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3) in thin film

Polymer	λ_max/nm		Eopt g^a/eV	E_LUMO^b/eV	E_HOMO^b/eV	ECV g^c/eV
Polymer	Sol.	Film	Eopt g^a/eV	E_LUMO^b/eV	E_HOMO^b/eV	ECV g^c/eV
P(AzProDOT-1)	594	601	1.60	－3.50	－5.36	1.86
P(AzProDOT-2)	587	603	1.55	－3.48	－5.38	1.90
P(AzProDOT-3)	613	626	1.58	－3.48	－5.40	1.92

表2. P(AzProDOT-1)、P(AzProDOT-2)和P(AzProDOT-3)的光谱和电化学相关数据

Table 2. Optical and electrochemical data of P(AzProDOT-1), P(AzProDOT-2) and P(AzProDOT-3)

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