Terminal Cyano-Functionalized Fused Bithiophene Imide Dimer-Based n-Type Small Molecular Semiconductors: Synthesis, Structure-Property Correlations, and Thermoelectric Performances

Dong Wang; Jianfeng Li; Kun Yang; Yimei Wang; Sang Young Jeong; Zhicai Chen; Qiaogan Liao; Bangbang Li; Han Young Woo; Xianyu Deng; Xugang Guo

doi:10.1021/acsami.2c20489

Terminal Cyano-Functionalized Fused Bithiophene Imide Dimer-Based n-Type Small Molecular Semiconductors: Synthesis, Structure-Property Correlations, and Thermoelectric Performances

ACS Appl Mater Interfaces. 2023 Feb 8. doi: 10.1021/acsami.2c20489. Online ahead of print.

Authors

Dong Wang^{1

2}, Jianfeng Li², Kun Yang³, Yimei Wang², Sang Young Jeong⁴, Zhicai Chen², Qiaogan Liao², Bangbang Li², Han Young Woo⁴, Xianyu Deng¹, Xugang Guo²

Affiliations

¹ Shenzhen Key Laboratory of Advanced Materials, School of Materials Science and Engineering, Harbin Institute of Technology, Shenzhen 518055, Guangdong, China.
² Department of Materials Science and Engineering, Southern University of Science and Technology (SUSTech), No. 1088, Xueyuan Road, Shenzhen 518055, Guangdong, China.
³ State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, Hunan, China.
⁴ Research Institute for Natural Sciences, Department of Chemistry, Korea University, Seoul 02841, South Korea.

PMID: 36753061
DOI: 10.1021/acsami.2c20489

Abstract

n-Doped small molecular organic thermoelectric materials (OTMs) hold advantages of high Seebeck coefficient and better performance reproducibility over their polymeric analogues; however, high-performance n-type small molecular OTMs are severely lacking. We report here a class of small molecular OTMs based on terminal cyanation of a bithiophene imide-based ladder-type heteroarene BTI2. It was found that the cyanation could effectively lower the lowest unoccupied molecular orbital (LUMO) level from -2.90 eV (BTI2) to -4.14 eV (BTI2-4CN) and thus lead to significantly improved n-doping efficiency. Additionally, terminal cyano-functionalization can maintain the close packing and efficient intermolecular charge transfer between these cyanated molecules, thus yielding high electron mobilities of up to 0.40 cm² V^-1 s^-1. Benefiting from its low LUMO-enabled efficient n-doping and high electron mobility, an encouraging n-type electrical conductivity of 0.43 S cm^-1 and power factor (PF) of 6.34 μW m^-1 K^-2 were achieved for tetracyanated BTI2-4CN, significantly outperforming those of its noncynated BTI2 (<10^-7 S cm^-1, PF undetectable) and dicyanated BTI2-2CN (0.24 S cm^-1, 1.78 μW m^-1 K^-2). These results suggest the great potential of the terminal cyanation strategy of ladder-type heteroarenes for developing high-performance small molecular OTMs.

Keywords: bithiophene imide; n-type organic semiconductors; organic thermoelectrics; structure−property correlations; terminal cyanation.