Semiconducting Copolymers with Naphthalene Imide/Amide π-Conjugated Units: Synthesis, Crystallography, and Systematic Structure-Property-Mobility Correlations

In a series of n-type semiconducting naphthalene tetracarboxydiimide (NDI)-dithiophene (T2) copolymers, structural and electronic properties trends are systematically evaluated as the number of NDI carbonyl groups is reduced from 4 in NDI to 3 in NBL (1-amino-4,5-8-naphthalene-tricarboxylic acid-1,8-lactam-4,5-imide) to 2 in NBA (naphthalene-bis(4,8-diamino-1,5-dicarboxyl)-amide). As the NDI-T2 backbone torsional angle falls the LUMO energy rises. However, the thienyl attachment regiochemistry also plays an important role in less symmetric NBL and NBA. Electron mobility is greatest for N2200 (0.17 cm(2) V-1 s(-1)) followed by PNBL-3,8-T2 and PNBA-2,6-T2 (0.11 cm(2) V-1 s(-1)), 0.02 cm(2) V-1 s(-1) in PNBL-4,8-T2, and negligible in PNBA-3,7-T2. Charge transport reflects a delicate balance between electronic backbone communication (optimum for N2200 and PNBL-4,8-T2), backbone planarity (optimum for PNBA-2,6-T2 and PNBL-3,8-T2), LUMO energy (optimum for N2200), pi-pi stacking distance (optimum for PNBA-2,6-T2), and film crystallinity (optimum for PNBA-2,6-T2 and N2200). These results offer generalizable insight into semiconducting copolymer design.

Automated summary

In this study, the structural and electronic properties trends of a series of n-type semiconducting copolymers were evaluated. The reduction of NDI carbonyl groups was found to increase the LUMO energy. Additionally, the thienyl attachment regiochemistry played a significant role in the performance of the copolymers.