Modulating Local Electron Density in NDI-Based CPs to Accelerate Photoinduced Electron Transfer for Ultrafast Violet Light Detection.

Abstract

Realizing rapid photoinduced electron transfer (PET) in donor-acceptor (D-A) systems is crucial. The relative energy levels of donors and acceptors, as well as the local electron density, are two important factors determining the rate of photoinduced electron transfer in donor-acceptor (D-A) systems. However, systematic studies on the structure-functional relationship regarding the local electron density factor, based on precise structural models are rarely reported. Herein, we report a strategy for fabricating donor-acceptor coordination polymers (D-A CPs) that facilitates PET and enables evaluation of reaction kinetics through local electron density modulation, using two NDI-based CPs, [Cd₂(dtNDI)(HBTC)(DMF)₄] (1) and [Cd₂(dtNDI)(H₂BTEC)(DMF)₄] (2), as proof-of-concept systems. By tuning carboxylate coordination-site electron density, compound 2 achieves a 10-fold PET rate increase (0.11953 → 1.15777 s^-1) compared with 1 and demonstrates rapid photochromism (4 s coloration). The extra carboxylates in H₂BTEC^2- lower the electron density at the coordination site, suppressing charge transfer (CT) while enhancing PET, which establishes that local electron density governs PET efficiency. Compound 2 also shows exceptional 400 nm violet-light sensitivity, making it ideal for violet-light detection and filtering applications. This work provides a precise structural model for mechanistic insights into PET control.