Zhen Yan, Yaqin Tian, Xubin Wang, Min Li, Min Qiao, Rong Miao*, Liping Ding*, and Yu Fang. https://doi.org/10.1002/adfm.76331

Organic fluorescent materials have attracted significant interest due to their unique electronic structure and optical properties, combined with distinct advantages such as structural diversity, and facile tunability. The electronic structure of fluorescent materials is critically important as it governs the photophysical properties of the corresponding compounds, which plays a key role in diverse applications including sensing, anti-counterfeiting, optical switches, and photoelectric displays. Systematic studies focusing on the ICT mechanism in molecular systems for advanced applications are urgently needed.

Precise regulation of the electronic structures of functional molecules remains a key challenge in the development of multifunctional materials. Herein, we report the systematic tuning of intramolecular charge transfer (ICT) characteristics in a series of acridine derivatives by introducing electron-withdrawing groups of varying strengths. Elevating the electron-withdrawing ability narrows the HOMO-LUMO gap, enhances ICT, and endows the three fluorophores with distinct solvatochromic and vapochromic behaviors. Strikingly, these fluorophores also exhibit solid-state chromism with high fluorescence quantum yields when doped into polymer matrices of different polarities, which effectively suppresses aggregation-caused quenching. Such multiphase polarity sensitivity enables a broad emission range spanning 450 ~ 660 nm, facilitating versatile applications in smart sensing, multicolor displays, and advanced information encryption. Notably, ACR-FCN, bearing malononitrile units as acceptor, displays a unique nonmonotonic response toward biogenic amines due to the alternation of its ICT properties. This allows visual, real-time monitoring of food freshness via a portable sensor, with a naked-eye detection limit of 1 ppm for putrescine. This work elucidates the critical role of acceptor modulation in tuning ICT properties and establishes a comprehensive workflow from molecular design to multifunctional applications.

Fig. 1. Schematic illustration of ICT strategy for acridine-based derivatives and functional applications

Fig. 2. (a) Schematic illustration of preparation of dye-loaded polymer films; (b) Illustration of the possible distribution of fluorophores within the polymer network; (c-f) The fluorescence spectra of ACR-FCN-doped polymer films and the reference films casted with pure polymers and ACR-FCN: (c) ACR-FCN/PB; (d) ACR-FCN/PS; (e) ACR-FCN/PMMA; and (f) ACR-FCN/PEG; (g) The fluorescence emission spectra of ACR-CHO-doped polymer films (ACR-CHO/PB, ACR-CHO/PS, ACR-CHO/PMMA, ACR-CHO/PEG); (h) The fluorescence emission spectra of ACR-SA-doped polymer films (ACR-SA/PB, ACR-SA/PS, ACR-SA/PMMA, ACR-SA/PEG); Insets of c-h: the images of the films taken under 365 nm UV light; (i) The CIE chromaticity coordinates of the fluorescent polymer films, Ⅰ represents ACR-CHO/PB and Ⅻ represents ACR-FCN/PEG; (j) The fluorescence quantum yields of the acridine compounds in solid state and polymer films; (k) Fluorescent patterns ‘EXIT’ fabricated by spraying solution of ACR-CHO/PEG (in THF) onto different substrates; (l) QR codes prepared by screen printing of ACR-CHO/PEG (in THF) on iron sheet and paper; (m) Fluorescent colorful letters “MATERIAL” prepared by drop casting on paper or optical glass.

First Author: Yan Zhen, doctoral candidate, Shaanxi Normal University

Correspondence Authors: Prof. Ding Liping and Assoc. Prof. Miao Rong, Shaanxi Normal University

Full Text Link: https://doi.org/10.1002/adfm.76331