Piezoelectric Micropower Harvester from Supramolecular Assembly of Chiral Ambipolar Chromophores

Abstract

This Article reveals highly promising piezoelectricity in chiral supramolecular assemblies of trialoxybenzamide-functionalized acceptor−donor−acceptor (ADA)-type ambipolar π-systems. In the three conjugated molecules (AD 1 A, AD 2 A, and AD 3 A), naphthalimide and thiophene units represent A and D, respectively, while the number of conjugated thiophene units is indicated by the number in the subscript. These systems exhibit helical supramolecular polymerization in hydrocarbon solvents, producing a fibrillar network. The most optimized structure (AD 2 A) (due to efficient charge separation and hence maximum polarizability) exhibits maximum open-circuit voltage (V oc ) of ∼2.2 V and short-circuit current density (J sc ) of ∼45.6 nA/ cm 2 at 17 N and 5 Hz, which can be considered as highly promising values in comparison to those recently reported for other organic small-molecule piezoelectric systems. Importantly, piezoelectricity almost disappears if the peripheral amide groups (responsible for H-bonding-driven supramolecular polymerization) are replaced with ester groups for the same AD 2 A chromophorecontaining building block, indicating the essential role of H-bonding-driven supramolecular polymerization in achieving long-range order and macroscopic polarization, which is supported by DFT calculations. Furthermore, replacing the chiral chains with achiral chains in the peripheral wedge also results in almost full suppression of the piezoelectric response, which highlights the significant role of helicity in such supramolecular polymers for the observed piezoelectricity. Finally, with the AD 2 A piezo device, the feasibility of monitoring human radial pulses is shown as a proof-of-concept biosensing demonstration.

Supramolecular Organic Ferroelectric Materials from Donor–Acceptor Systems

“…Recently, we have shown that the FE hydrogen-bonded supramolecular polymers of ADA-type ambipolar π-systems, when cast into flexible device structures, could be useful for a sensitive piezo biosensor to monitor wrist pulses stimulated by normal human physiological action. [81] Cascade D-A organic FE layers, between graphene sheets, were theoretically predicted for application in solar cells. The functionality of the presented system was compared to that of integrated heterojunctions, in which the addition of the electron and hole transport layers was shown not to be necessary for electron and hole transport across the layers.…”

“…Further, they demonstrated a self‐powered biomedical sensor from the device to monitor physiological signal monitoring. Recently, we have shown that the FE hydrogen‐bonded supramolecular polymers of ADA‐type ambipolar π‐systems, when cast into flexible device structures, could be useful for a sensitive piezo biosensor to monitor wrist pulses stimulated by normal human physiological action [81] . Cascade D‐A organic FE layers, between graphene sheets, were theoretically predicted for application in solar cells.…”

“…Nevertheless, low piezo‐response and lack of adequate understanding on the structure‐property correlation have limited their applications till now. This inspired us to examine PE‐response of the supramolecular polymers (Figure 10) of ambipolar π‐systems (Figure 9), [81] particularly those exhibited prominent FE behaviour at RT.…”

Light-regulated morphology control in supramolecular polymers

“…In this regard, the research group of Stupp studied an amphiphilic oligopeptide tethered with an ONB photo-protecting group (32) in the junction of the alkyl chain and peptide segment (Fig. 15).…”

“…Subsequently, it is possible to externally regulate the efficacy of a biologically active motif using light and the site-specific delivery of payloads is also viable. The morphological changes are often associated with the change in the anisotropy of the resulting sample which impacts the electronic properties including conductivity, 28,29 piezo-response, [30][31][32] etc. and provides the opportunity to fabricate controllable smart materials.…”