Surface-Induced Donor-Acceptor Charge-Transfer Interaction in Crystallization-Driven Two-Dimensional Assembly of Poly(L-Lactide) and Its Impact on Piezoelectric Performance.

Precise 2D architectures with tailorable surface properties from organic soft materials remain a formidable scientific challenge. This work demonstrates crystallization-driven self-assembly (CDSA) as a simple yet powerful strategy to obtain discrete 2D microcrystals from biocompatible semicrystalline chromophore end-capped poly(L-lactide) (PLLA) scaffolds, serving as well-defined 2D templates for supramolecular engineering of surface properties via donor-acceptor (D-A) charge-transfer (CT) interactions. As a representative case study, we show that CDSA yields diamond-shaped 2D PLLA platelets with electron-deficient, cationic naphthalene diimide (NDI) acceptors pre-organized on the 2D surface. This enables electrostatically induced D-A interactions with anionic electron-rich dihydroxynaphthalene (DHN) guests, allowing exploration of their functional utility in piezoelectric (PE) energy harvesting. The synergistic effect of inherently non-centrosymmetric PLLA chain packing and CT-interactions on the 2D surface results in efficient macroscopic polarization switching, leading to prominent piezoelectricity (d33 ∼14 pm/V) without poling. This enhanced PE response was exploited for micropower energy harvesting as demonstrated by a piezogenerator functionality (output Voc ∼ 1.30 V and Jsc ∼ 0.5 µA/cm2), showing potential proof-of-concept application as an efficient physiological sensor. Multiple control experiments confirm that without such well-defined 2D architectures, PE functions do not emerge, establishing CDSA-engineered PLLA 2D platforms as emerging functional materials for energy harvesting beyond structural aesthetics.