Octupolar Acrylonitrile‐Bridged 2D‐Conjugated Polymers Enable Bright Far‐Red Emission with Intense Two‐Photon Absorption via Alkoxylation Chemistry

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 17; no. 36
• Main Authors: Mo, Chunshao, Yang, Meijia, Cheng, Zhixue, Tang, Xikang, Yang, Lifen, Su, Ruonan, Li, Jing, Feng, Jiangshan, Fang, Long, Yang, Kexin, Chen, Zhuanggui, Yu, Dingshan
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.09.2021
• Subjects: 2D‐conjugated polymers; alkoxylation chemistry; Biocompatibility; Chromophores; Conjugation; Coplanarity; donor‐acceptor; Emission spectra; far‐red fluorescence; Fluorescent indicators; Nanotechnology; Phosphors; Photon absorption; Photons; Polymers; Steric hindrance; Substitutes; Tetrahydrofuran; two‐photon absorption; White light
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202100955

Herein, alkoxylation chemistry is introduced as a “one‐stone‐three‐birds” solution for exploring a new family of highly‐fluorescent octupolar 2D‐conjugated organic polymers/frameworks (OCOPs/OCOFs) combining far‐red emission, high fluorescence quantum yield (QY), and strong two‐photon absorption (TPA). Both alkoxy‐substituted OCOP and OCOF comprising acrylonitrile‐bridged strongly‐coupled donor3‐(acceptor core) chromophores densely packed in either disordered or ordered forms, exhibit significantly redshifted emission. They produce high QY of 22.2% and 27.8% in tetrahydrofuran, large TPA cross section of 600 and 1124 GM, and 2–3 folds and 15–30 folds that of non‐alkoxylate amorphous counterpart respectively. Combined theoretical and experimental studies reveal unique “one‐stone‐three‐birds” role of the alkoxylation in realizing red‐shifted‐emission, improved QY and TPA enabled by inducing steric hindrance effect for weakened π–π stacking, and triggering p–π conjugation effect for electronically engineering octupolar chromophores, while the crystalline engineering enables enforced coplanarity conformation and improved π–electron delocalization for further improved QY and TPA. The robust and biocompatible pentoxy‐substituted polymer can be used not only as metal‐free red‐emissive phosphor for efficient warm white light‐emitting diodes, but also as efficient two‐photon fluorescence probes for bio‐imaging. A “one‐stone‐three‐birds” alkoxylation solution is introduced for developing a new class of highly‐fluorescent, acrylonitrile‐bridged, and octupolar 2D conjugated polymers/frameworks with far‐red emission, high quantum yield, and large two‐photon absorption cross section simultaneously, demonstrating versatile uses for warm white light‐emitting diodes and in vitro/vivo bioimaging.