Junwoo Park Group

1. Non-equilibrium Charge Transport in Molecules

What does a charge carrier do to the molecule it passes through?

Charge as an Active Energy Carrier: A charge carrier is not a passive probe but a packet of energy. We have shown that when it resonates with a molecular orbital, it deposits energy, drives conformational change, and rewrites the conductance of the very molecule it passes through—a feedback loop that can be predicted and chemically tuned.

Molecular Memristors: Because current reshapes the molecule, a molecule can remember; because the reshaping is stochastic, it can act as a p-bit whose statistics are set by chemistry; because light couples to the same channel, it can behave as an optoelectronic synapse. These devices are the functional face of charge–molecule interaction and building blocks for our second theme.

Image credit: kishore kumar / Getty Images

2. Learning in Hardware

Can a material learn, infer, and adapt by itself, without software?

Why Learning Should Live in Matter, Not in Code: Today’s AI learns in software detached from any physical substrate, under rules fixed in advance—which is why it still lacks what the brain takes for granted: context-dependent, continual, uncertainty-driven, and few-shot learning. The brain, by contrast, chose slow, diffusive chemical synapses over fast electrical ones. We suspect the uncertainty of diffusing molecules is not a compromise but the very source of that flexibility.

Physical Computing Systems: We build systems in which the physical and chemical laws of a material are themselves the learning rules. In a fluidic synapse, ions and chemical species carry information, and a chemical signal released into a shared electrolyte reaches every synapse at once—a natural third factor for reinforcement learning that mirrors neuromodulation and cannot be wired into electronic hardware.

3. Ion–Electron Coupling at Solid–Liquid Interfaces

How do ions in a liquid communicate with electrons in a solid?

Coupling across Electric Double Layer: The electric double layer governs catalysis, energy storage, sensing, and how water behaves on a surface, yet its coupling to the solid’s electronic structure is poorly understood. We discovered that moving droplets drive charge flow in a semiconductor (ionovoltaics, J. Am. Chem. Soc. 139, 10968 (2017)), and have since shown the reverse: perturbing the electrons with light reversibly changes interfacial energy and wettability.

Multimodal Modulation of Interfaces: Each of these inputs offers a handle on the interface. We map how molecular-scale modulation propagates to macroscopic behavior—wetting, sliding, bouncing, and friction of drops—using interface-specific spectroscopy, scanning-probe, and surface-force measurements, toward interfaces that can be designed and controlled.

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