Piezoelectric Micropower Harvester from Supramolecular Assembly of Chiral Ambipolar Chromophores

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 chromophore-containing 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.