Abstract
Molecular rotors have played an important role in recent materials chemistry. Although several studies on functional materials containing molecular rotors have been reported for fluorescence sensing, this concept has yet to be realized in two-dimensional (2D) materials. Here we report the preparation of all-carbon, π-conjugated 2D porous organic nanosheets, named NUS-24, which contain flexible tetraphenylethylene (TPE) units as the molecular rotors. NUS-24 nanosheets exhibit high stability, large lateral size, and ultrathin thickness (2–5 nm). The dynamic TPE rotors exposed on the surface of NUS-24 nanosheets can be restricted in the aggregated state with different water fractions, which is reminiscent of the aggregation-induced emission mechanism, thereby leading to the size-selective turn-on fluorescence by volatile organic compounds. Significantly, the ultrathin 2D nanosheets and its composite membranes show much higher sensitivity and selectivity toward Fe3+ ions and nitro-containing compounds sensing, suggesting their potential applications in explosive detection and environmental monitoring.
Highlights
Molecular rotors have played an important role in recent materials chemistry
The central olefin stators of TPE1 linker are surrounded by two free peripheral phenyl rings, which can act as molecular rotors for turn-on fluorescent sensing, thereby forming a planar surface with protruding free dynamic TPE rotors on top
Compared to NUS-24 bulk powder, the exfoliated NUS-24 nanosheets exhibit stronger turn-on fluorescence upon contact with electron-rich volatile organic compounds (VOCs), and the fluorescence enhancement is positively correlated with the molecular size of VOC molecules
Summary
Molecular rotors have played an important role in recent materials chemistry. several studies on functional materials containing molecular rotors have been reported for fluorescence sensing, this concept has yet to be realized in two-dimensional (2D) materials. The rational design of artificial molecular machines is an important objective in synthetic chemistry and functional materials research, and it has been achieved in the pioneering work by Stoddart[1,2,3], Feringa[4,5], and Leigh[6,7,8] Among these molecular machines, fluorescent molecular rotors have received wide attention recently due to their importance in broadening the fundamental understanding of dynamic molecular systems and their wide applications in areas including biological detection[9,10,11,12,13], materials chemistry[14,15], membrane engineering[16], and so on. Feng and co-workers synthesized a series of extended polycyclic aromatic hydrocarbons (PAHs) or graphene molecules for electronic device[30,31,32,33] These novel 2D materials have large aspect ratios with fully exposed basal planes, and demonstrate good catalytic and electrochemical properties as well as being promising platforms for chemical sensing and biosensing applications[34]. The molecular rotors would enhance the sensitivity and selectivity of these fluorescent sensors for specific sensing applications
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