Molecular Dynamics Study of the Thermodynamics of Integer Charge Transfer vs Charge-Transfer Complex Formation in Doped Conjugated Polymers
Molecular Dynamics Study of the Thermodynamics of Integer Charge Transfer vs Charge-Transfer Complex Formation in Doped Conjugated Polymers
复制标题
掺杂共轭聚合物中整数电荷转移与电荷转移络合物形成的热力学的分子动力学研究
DOI：
10.1021/acsami.2c06449
复制
发表时间：
2022
影响因子：
9.5
通讯作者：
Schwartz, Benjamin J.
中科院分区：
文献类型：
--
作者：
Wu, Eric Chih-Kuan;Salamat, Charlene Z.;Tolbert, Sarah H.;Schwartz, Benjamin J.
分子掺杂剂如2,3,5,6-四氟-7,7,8,8-四氰喹诺二甲烷（F4TCNQ）可以通过两种不同的方式与共轭聚合物如聚（3-己基噻吩-2,5-二基）（P3HT）相互作用：它们可以进行整数电荷转移（ICT）或形成部分电荷转移配合物（CTC）。两者都是在实验中看到的，但CTC的特征一直具有挑战性，因此很难回答以下问题。哪种晶型更稳定？它们是否有类似的形成障碍？有没有热力学途径将一种转化为另一种？本文采用全原子分子动力学模拟方法研究了块状掺杂f4tcnq的P3HT的结构和热力学，利用热力学积分计算了相对自由能。我们发现ICT和CTC多晶具有相似的热力学稳定性。然而，产生ICT多晶的障碍比制造CTC多晶的障碍要低，因为ICT多晶的临界核很小，而CTC多晶的临界核比我们可以模拟的要大。此外，模拟热退火表明，CTC晶型转化为ICT晶型的激活势垒相对较小。总的来说，模拟解释了f4tcnq掺杂P3HT的观察结构和热力学，并为针对不同应用目标生产所需的多晶片提供指导。
Molecular dopants such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) can interact with conjugated polymers such as poly(3-hexylthiophene-2,5-diyl) (P3HT) in two different ways: they can undergo integer charge transfer (ICT) or they can form a partial-charge-transfer complex (CTC). Both are seen experimentally, but the CTC has been challenging to characterize, making it difficult to answer questions such as the following. Which polymorph is more stable? Do they have similar barriers for formation? Is there a thermodynamic route to convert one to the other? Here, we study the structure and the thermodynamics of bulk F4TCNQ-doped P3HT with all-atom molecular dynamics simulations, using thermodynamic integration to calculate the relative free energies. We find that the ICT and CTC polymorphs have similar thermodynamic stabilities. The barrier to create the ICT polymorph, however, is lower than that to make the CTC polymorph, because the ICT polymorph has a small critical nucleus, but the critical nucleus for the CTC polymorph is larger than what we can simulate. Moreover, simulated thermal annealing shows that the activation barrier for converting the CTC polymorph to the ICT polymorph is relatively modest. Overall, the simulations explain both the observed structures and the thermodynamics of F4TCNQ-doped P3HT and offer guidelines for targeting the production of a desired polymorph for different applications.