Piezoelectric Micropower Harvester from Supramolecular Assembly of Chiral Ambipolar Chromophores

ThisArticle reveals highly promising piezoelectricityin chiralsupramolecular assemblies of trialoxybenzamide-functionalized acceptor-donor-acceptor(ADA)-type ambipolar & pi;-systems. In the three conjugated molecules(AD(1)A, AD(2)A, and AD(3)A), naphthalimideand thiophene units represent A and D, respectively, while the numberof conjugated thiophene units is indicated by the number in the subscript.These systems exhibit helical supramolecular polymerization in hydrocarbonsolvents, producing a fibrillar network. The most optimized structure(AD(2)A) (due to efficient charge separation and hence maximumpolarizability) exhibits maximum open-circuit voltage (V (oc)) of & SIM;2.2 V and short-circuit current density(J (sc)) of & SIM;45.6 nA/cm(2) at 17 N and 5 Hz, which can be considered as highly promising valuesin comparison to those recently reported for other organic small-moleculepiezoelectric systems. Importantly, piezoelectricity almost disappearsif the peripheral amide groups (responsible for H-bonding-driven supramolecularpolymerization) are replaced with ester groups for the same AD(2)A chromophore-containing building block, indicating the essentialrole of H-bonding-driven supramolecular polymerization in achievinglong-range order and macroscopic polarization, which is supportedby DFT calculations. Furthermore, replacing the chiral chains withachiral chains in the peripheral wedge also results in almost fullsuppression of the piezoelectric response, which highlights the significantrole of helicity in such supramolecular polymers for the observedpiezoelectricity. Finally, with the AD(2)A piezo device,the feasibility of monitoring human radial pulses is shown as a proof-of-conceptbiosensing demonstration.