State Localization and Selective Charge Filtering Near a Null Point

TL;DR

This study experimentally verifies null points in molecular aggregates, demonstrating state localization and selective charge filtering crucial for photovoltaic design, supported by a vibronic theory.

Contribution

First experimental observation of null points in molecular systems, revealing charge separation and localization with implications for photovoltaic material design.

Findings

Charge separation via locally excited-charge transfer states.

Polarization anisotropy confirms state localization and selective charge filtering.

Vibronic theory explains null point behavior and guides synthetic parameters.

Abstract

Null points in synthetically tunable molecular aggregates are predicted to generate flat energy bands analogous to those known in strongly correlated condensed-matter physics. For chemistry, null points provide a powerful design principle for photovoltaic materials with selective charge filtering similar to photosynthesis. However, null points have never been experimentally verified because their defining prediction - state localization with selective electron or hole transfer - has remained unobserved. Here, using a donor-acceptor dyad as a minimal model, we provide the first experimental observation of a null point. Impulsive pump-probe measurements reveal charge separation through a near-instantaneously generated locally excited-charge transfer (LE-CT) intermediate that emerges upon solvent stabilization of CT states. Polarization anisotropy directly reveals state localization and selective charge-filtering, spanning balanced electron-hole transfer to selective hole filtering consistent with synthetic design. A generalized vibronic theory of null points explains these observations and identifies the ideal synthetic parameters for achieving null points which are protected from the vibrational bath.