Fluorescent Porous Organic Frameworks Containing Molecular Rotors for Size-Selective Recognition

Abstract

Fluorescent porous materials have been under intensive investigation recently, because of their wide applications in molecular recognition and chemical sensing. However, it is a great challenge to achieve size selectivity and sensing linearity for molecular recognition. Herein, we report a series of porous organic frameworks (POFs) containing flexible tetraphenylethylene (TPE) moieties as molecular rotors with responsive fluorescent behavior. These fluorescent POFs exhibit size-selective turn-on fluorescence for the effective chemical sensing of volatile organic compounds (VOCs), which can be attributed to the different degrees of motion restriction of flexible TPE rotors by various VOCs, leading to the partially freezing of rotors in more fluorescent conformations. Significantly, a linear aggregation-induced emission (AIE) relationship is observed between the fluorescent POFs and the VOCs over a wide range of concentrations, which is highly beneficial for quantitative sensing applications. The gas-phase detection of arene vapors using POFs is also proven with unprecedentedly high sensitivity, selectively, and recyclability. The mechanism of responsive fluorescence in POFs is further investigated using molecular simulations and density functional theory (DFT) calculations.

Porous Organic Polymers for CO2 Storage and Conversion Reactions

“…Dong et al. have reported a series of fluorescent porous organic frameworks (NUS‐20‐23) by using Pd‐catalyzed Suzuki or Sonogashira C−C cross‐coupling reactions between tetrahedral tetrakis aromatic bromides and diboronic acid or dialkyne as monomers . NUS‐20/21/22/23 showed high BET surface areas (up to 900 m 2 g −1 ) and large micropores of dimensions 12.3–14.1 Å.…”

Homo‐ and Copolycyclotrimerization of Aromatic Internal Diynes Catalyzed with Co2(CO)8: A Facile Route to Microporous Photoluminescent Polyphenylenes with Hyperbranched or Crosslinked Architecture

“…P(I-co-IV)1 and P(I-co-IV)2 also showed a significant increase in the adsorbed amount for p/p 0 > 0.9, which reflected the interparticle capillary condensation of N 2 and the filling of mesopores. All adsorption-active samples showed significant adsorption/desorption hysteresis with unclosed hysteresis loops, [14,[32][33][34] indicating that N 2 diffusion through well-accessible permanent pores was most likely accompanied by N 2 penetration into pores with restricted access as discussed in ref. [35] During the N 2 adsorption/desorption measurement, the polycyclotrimers outlined in Table 1 may undergo minor conformational changes resulting from the rotation of pendant phenyl groups and/or 1,4-phenylene segments, [36][37][38] which may affect the ability of some pores to capture and/or release N 2 .…”

Porous Organic Frameworks: Advanced Materials in Analytical Chemistry

“…Furthermore, after removing these electron‐donating arenes, the previously enhanced fluorescence intensity takes only a few minutes to recover back to the normal level because the volatile arenes can easily escape from the frameworks of TAT‐COF‐2, which indicated that TAT‐COF‐2 can be conveniently reused for the detection of electron rich arenes. Dong et al reported constructing a series of POFs (NUS‐20–NUS‐23, S BET = 368–900 m 2 g −1 ) based on flexible AIE‐active TPE units as molecular rotors through Suzuki–Miyaura or Sonogashira–Hagihara reactions. The POFs presented noticeably “turn‐on” or “turn‐off” fluorescence emission upon exposure to various arenes (also known as volatile organic compounds, VOCs).…”

“…The difference in the LUMO energy state between NUS‐20 fragment and various VOC analytes [Δ E LUMO = E LUMO (arene vapors) – E LUMO (NUS‐20)] is 1.49, 1.32, 1.26, 0.85, and −1.25 eV for mesitylene, toluene, benzene, chlorobenzene, and nitrobenzene, respectively. Adapted with permission . Copyright 2016, American Chemical Society.…”