Unveiling the sensing mechanism at the molecular level: a DFT study on the disaggregation of perylene diimide radical anion pimers

Authors & Affiliations

Hanlin Gan^ab, Haiquan Zhang^*ac, Yuguang Ma^ab, Qinglin Jiang^*ab

^a State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China
^b Guangdong Basic Research Center of Excellence for Energy and Information Polymer Materials, Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates, South China University of Technology, Guangzhou 510640, P. R. China
^c State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, P. R. China
* Corresponding authors: E-mail: jiangql@scut.edu.cn (Q. Jiang), hqzhang@ysu.edu.cn (H. Zhang)

Abstract

The radical anion of amide-functionalized perylene diimide (TFPDIOH˙⁻) aggregates into a pimer that is stabilized through pancake bonding. In the presence of primary amines, this pimer can undergo disaggregation, offering potential for responsive organic sensors. In this study, density functional theory (DFT) calculations were employed to elucidate the sensing mechanism, which can be represented as follows: 1/2[TFPDIOH]₂²⁻ + nBuNH₂ → [nBuNH₂·TFPDIOH]˙⁻.

Computational results reveal that steric hindrance from the bulky substituents on the amide positions weakens π-stacking interactions, thereby allowing strong hydrogen bonding to induce pimer disaggregation. The phenolic hydroxyl group on the substituent forms a low-barrier hydrogen bond (LBHB) with nBuNH₂, which is characterized by a short N⋯O distance, high ρ BCP, 3c–4e bonding pattern, and nearly barrierless proton transfer. The electron-withdrawing fluorine atoms on the substituent enhance hydroxyl acidity, further stabilizing LBHB formation.

These findings reveal the LBHB-driven disaggregation mechanism and demonstrate that the rational combination of pancake bonding and LBHB interactions offers a novel strategy for developing π-radical-based organic sensors with enhanced sensitivity.

Research Highlights

Elucidated the disaggregation mechanism of perylene diimide radical anion pimers via DFT calculations.
Identified low-barrier hydrogen bond (LBHB) as the core driving force for pimer disaggregation in the presence of primary amines.
Bulky amide substituents weaken π-stacking, facilitating LBHB-induced disaggregation.
Electron-withdrawing fluorine atoms enhance hydroxyl acidity, stabilizing LBHB formation.
Proposed a new strategy for π-radical-based sensor design by combining pancake bonding and LBHB interactions.

Computational Methodology

Density Functional Theory (DFT) calculations were employed to investigate the pimer structure, intermolecular interactions (pancake bonding, hydrogen bonding), and disaggregation process. Key computational details include:

Structural optimization and energy calculations for pimers and hydrogen-bonded complexes.
Analysis of steric hindrance, π-stacking strength, and LBHB characteristics (N⋯O distance, ρ BCP, bonding pattern).
Evaluation of the effect of electron-withdrawing substituents (fluorine atoms) on hydroxyl acidity and LBHB stability.

Supplementary Information & Links

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Supplementary information includes structural indicators for pimers, spin density distribution, computational results of neutral pimers, and Cartesian coordinates of all calculated structures.