Stefano Pecorario1,2,Jeroen Royakkers3,Hugo Bronstein4,Mario Caironi1
Istituto Italiano di Tecnologia1,Politecnico di Milano2,Maastricht University3,University of Cambridge4
Stefano Pecorario1,2,Jeroen Royakkers3,Hugo Bronstein4,Mario Caironi1
Istituto Italiano di Tecnologia1,Politecnico di Milano2,Maastricht University3,University of Cambridge4
Molecular encapsulation is a powerful synthetic concept that can be used to study polymer chains (or molecules) in isolation by shielding the conjugated backbone with protective macrocycles, and preventing electronic cross communication between the π-systems. Here, we present a molecularly encapsulated form of the naphthalene diimide bithiophene copolymer PNDIT2, one of the most widely used semiconducting polymers with high charge mobility for n-type field-effect transistors and non-fullerene acceptors in organic photovoltaic blends. We introduced enclosing macrocycles covalently bonded to the bithiophene units, while the naphthalene diimide moieties are left open for intermolecular interactions. We found that the encapsulated equivalent shows more backbone planarity when compared to PNDIT2. Furthermore, molecular encapsulation prevents the polymer chains from pre-aggregating in common organic solvents, while allowing π-stacking in the solid state and fostering thin film crystallinity through an intermolecular-lock mechanism. As a result, field-effect transistors still exhibit n-type semiconducting behavior, despite charge mobility being lower than in PNDIT2 as a result of the lack of the fibrillar microstructure that results from pre-aggregation in solution. Thus, molecular encapsulation appears as an effective method to adjust the nanomorphology of cast films while preserving the electrical structure of the core polymer and the thin film charge transport properties.<br/>References:<br/>(1) Pecorario, S.; Royakkers, J.; Scaccabarozzi, A. D.; Pallini, F.; Beverina, L.; Bronstein, H.; Caironi, M. Effects of Molecular Encapsulation on the Photophysical and Charge Transport Properties of a Naphthalene Diimide Bithiophene Copolymer. <i>Chem. Mater. </i> 2022. https://doi.org/10.1021/acs.chemmater.2c01894.<br/>(2) Royakkers, J.; Bronstein, H. Macrocyclic Encapsulated Conjugated Polymers. <i>Macromolecules </i>2021. https://doi.org/10.1021/acs.macromol.0c01916.