Zhen Yan, Taihong Liu,* Liping Ding,* and Yu Fang. https://doi.org/10.1021/acscentsci.6c00693

As an emerging frontier in functional material science, multicolor fluorescent smart materials have garnered significant interest due to their inherent versatility and precisely tunable fluorescent characteristics, enabling the development of increasingly sophisticated and functional platforms. In this Outlook, we summarize the recent advances in small organic molecules-based multicolor fluorescent materials, covering their design principles, optical properties, and versatile applications. The various strategies for achieving multicolor fluorescence emission could range from classic approaches based on modulation of electronic excited states and molecular intrinsic structure to newly emerging methods such as molecular conformation switching and regulation of molecular aggregation/packing. We also present the advanced applications of the multicolor fluorescent materials driven by these design strategies, including fluorescence sensing, anti-counterfeiting, information encryption and decryption. Finally, an outlook into the main challenges and future opportunities for multicolor fluorescent materials is previewed, aiming to accelerate the advancement of smart materials and devices. We hope these insights will inspire further innovative research on multicolor fluorescent smart materials and their advanced applications.

Multicolor fluorescent smart materials still face challenges such as unclear structure-property relationships, insufficient optical performance, and multi-stimulus responsiveness. Machine learning offers a powerful avenue to accelerate molecular design and predict photophysical properties; when integrated with in-situ characterization techniques and theoretical modeling, it can elucidate the underlying photophysical mechanisms. The incorporation of such materials into flexible substrates holds promise for advancing wearable sensor technologies, while improved biocompatibility further supports their application in personalized healthcare. The core objective lies in designing materials featuring multiple tunable luminescent centers that reconcile rapid switching capability with high color purity, guided by a profound understanding of the structure-property-function relationship.

Fig. 1. Jablonski diagrams that illustrate different photophysical mechanisms: (a) intramolecular charge transfer (ICT); (b) fluorescence resonance energy transfer (FRET); (c) excited state intramolecular proton transfer (ESIPT); (d) Structure of thiazolothiazole dye and the solvent-dependent fluorescence property; (e) Nme-BEN structure and reversible color change of Nme-BEN powder upon irradiation. S₀ represents the ground state, and S₁ the first singlet excited state. Abbreviations: Abs for absorption, LE for locally excited state, CT for charge transfer, TICT for twisted intramolecular charge transfer, Em for emission, J(λ) expresses the degree of spectral overlap between the donor emission and the acceptor absorption; RPT for reverse proton transfer, R for the distance between the donor and acceptor, FL for fluorescence.

Fig. 2. (a) Several functional groups based on molecular structure changes: (a-1) cis/trans isomerization; (a-2) open/closed-ring isomerization; (a-3) protonation/deprotonation process; (b) Repeating the process of light patterning and dark erasing based on spiropyran structure; Photochromic multicolor spiropyran hydrogels at specific pH values upon irradiation; (c) Color change of DPA-TPE-Py test strips in response to diethyl chlorophosphite vapor.

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

Correspondence Authors: Prof. Ding Liping and Liu Taihong, Shaanxi Normal University

Full Text Link: https://doi.org/10.1021/acscentsci.6c00693