Perylene diimide architecture-based electromechanical sensors: a systematic experimental and theoretical framework for the comparative analysis and study of the transduction mechanism†

This work presents a detailed comparative study on the effects of functional groups on engineered PDI (perylene diimide) compounds for pressure and breath sensing applications using experimental findings and density functional theory (DFT)-based theoretical calculations. The results demonstrate that the deposition of N-substituted perylene-3,4-dicarboxylic acid imide derivatives (PDI-1, PDI-2, PDI-3, and PDI-4) with different functional groups (3-aminopentane, 2,5-di-tert-butylaniline, 1-phenylethylamine, etc.) on the paper substrate forms a moderately conducting percolating molecular network with enhanced pressure and breath-sensing performances. The determined pressure sensitivity value for PDI-1 was 0.315 kPa⁻¹, for PDI-2 was 1.266 kPa⁻¹, for PDI-3 was 0.749 kPa⁻¹, and for PDI-4 was 2.120 kPa⁻¹. Among all the fabricated PDI-based pressure sensors, PDI-4 displayed maximum sensitivity owing to the inherent asymmetric nature of the compound with two different terminal substituents. The sensor displayed a steady response of up to ∼8000–10 000 cycles, confirming the mechanical sturdiness of fabricated PDI-based pressure sensors. The DFT-based theoretical analysis offers detailed insight into the transduction mechanism of pressure and breath sensing for different PDI molecules, wherein it can be surmised that both the structural configuration and electronic properties of PDI-4 (PDI-1) are suitable (undesirable) to ensure a large increase in intermolecular tunneling components and, thereby, in the overall conductivity of the percolating network under applied pressure. Hence, PDI-4 (PDI-1) is the most (least) favorable PDI molecule for pressure sensing applications. In contrast, a moderate response can be expected in PDI-2 and PDI-3 during pressure sensing as two competing factors influence the overall efficacy of transduction in these cases.