Solvent-free, nonvolatile, room-temperature alkylated-π functional molecular liquids (FMLs) are rapidly emerging as a new generation of fluid matter. However, precision design to tune their physicochemical properties remains a serious challenge because the properties are governed by subtle π-π interactions among functional π-units, which are very hard to control and characterize. Herein, we address the issue by probing π-π interactions with highly sensitive pyrene-fluorescence. A series of alkylated pyrene FMLs were synthesized. The photophysical properties were artfully engineered with rational modulation of the number, length, and substituent motif of alkyl chains attached to the pyrene unit. The different emission from the excimer to uncommon intermediate to the monomer scaled the pyrene-pyrene interactions in a clear trend, from stronger to weaker to negligible. Synchronously, the physical nature of these FMLs was regulated from inhomogeneous to isotropic. The inhomogeneity, unexplored before, was thoroughly investigated by ultrafast time-resolved spectroscopy techniques. The result provides a clearer image of liquid matter. Our methodology demonstrates a potential to unambiguously determine local molecular organizations of amorphous materials, which cannot be achieved by conventional structural analysis. Therefore this study provides a guide to design alkylated-π FMLs with tailorable physicochemical properties.
The formation of a metastable supercooled alkyl-π molecular liquid was prohibited by subtle alteration of the molecular structure.
The rapid discrimination of nitrophenol isomers has been a long-standing challenge because of the tiny structural differences among the isomers. In this study, a fluorescent sensor array based on three different-color emitting gold nanoclusters (Au NCs) that were functionalized with three different ligands and a cocapping ligand β-cyclodextrin (β-CD) has been constructed for the facile discrimination of three nitrophenol isomers via the linear discriminant analysis of isomer-induced fluorescence quenching patterns. The fluorescence quenching occurs in two steps: first, β-CDs adsorb nitrophenol isomers onto the surface of Au NCs via a host–guest interaction; second, each nitrophenol isomer quenches the fluorescence of a specific type of Au NCs through diverse inner filter effect. The different binding affinities between β-CD and each nitrophenol isomer, as well as the distinct quenching efficiencies of the isomers on the fluorescence of each Au NCs, enable an excellent discrimination of the three isomers at a concentration of 5 μM, when linear discriminant and hierarchical cluster analyses were smartly combined. In addition, even a mixture of two isomers could be distinguished with the proposed sensor array. The practicability of this developed sensor array is validated by a high accuracy (98.0%) examination of 51 unknown samples containing a single isomer or a mixture of two isomers.
Solvent‐free luminous molecular liquids (LMLs) are a new generation of soft matter which exhibit uncharged, nonvolatile, and fluidic nature and emit intense and homogeneous luminescence in the condensed state. They can be produced readily on the gram scale by modifying luminophores with bulky, flexible, and low‐melting side chains. Their performance can be facilely enriched by blending them with commercially available functional substances. Therefore, since their active optoelectronic properties were perceived a decade ago, LMLs have been regarded as promising contributing components in the burgeoning field of flexible and wearable light‐emitting devices. Recently, richer insights into LMLs have triggered various new applications. Additionally, unexpected phase behavior and photophysical properties have been discovered coincidentally. Therefore, the sensible and sophisticated molecular design principles of LMLs are still being augmented to guarantee predictable, steady, and consistent end‐use performance. This review summarizes the latest developments in LMLs, including molecular design principles, regulation and enrichment of their photophysical properties, and their versatile applications. Additionally, a prediction of the perspectives of LMLs in the near future is presented at the end.
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