Charge Resonance and Photoinduced Charge Transfer in Bis(N, N-dimethylaminophenyl-tetracyanobutadiene)-diketopyrrolopyrrole Multimodular System

Charu Popli; Youngwoo Jang; Rajneesh Misra; Francis D'Souza

doi:10.1021/acs.jpcb.3c01528

Charge Resonance and Photoinduced Charge Transfer in Bis(N, N-dimethylaminophenyl-tetracyanobutadiene)-diketopyrrolopyrrole Multimodular System

J Phys Chem B. 2023 May 18;127(19):4286-4299. doi: 10.1021/acs.jpcb.3c01528. Epub 2023 May 3.

Authors

Charu Popli¹, Youngwoo Jang², Rajneesh Misra¹, Francis D'Souza²

Affiliations

¹ Department of Chemistry, Indian Institute of Technology, Indore 453552, India.
² Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5017, United States.

PMID: 37133351
DOI: 10.1021/acs.jpcb.3c01528

Abstract

Intervalence charge transfer (IVCT) or charge resonance is often observed in redox-active systems encompassed of two identical electroactive groups, where one of the groups is either oxidized or reduced and serves as a model system to improve our fundamental understanding of charge transfer. This property has been explored in the present study in a multimodular push-pull system carrying two N,N-dimethylaminophenyl-tetracyanobutadiene (DMA-TCBD) entities covalently linked to the opposite ends of bis(thiophenyl)diketopyrrolopyrrole (TDPP). Electrochemical or chemical reduction of one of the TCBDs promoted electron resonance between them, exhibiting an IVCT absorption peak in the near-infrared area. The comproportionation energy, -ΔG_com, and equilibrium constant, K_com, evaluated from the split reduction peak were, respectively, 1.06 × 10⁴ J/mol and 72.3 M^-1. Excitation of the TDPP entity in the system promoted the thermodynamically feasible sequential charge transfer and separation of charges in benzonitrile, wherein the IVCT peak formed upon charge separation served as a signature peak in characterizing the product. Further, transient data analyzed using Global Target Analysis revealed the charge separation to take place in a ps time scale (k ∼ 10¹⁰ s^-1) as a result of close positioning and strong electronic interaction between the entities. The significance of IVCT in probing excited-state processes is evidenced by the present study.