Chinese Chemical Letters
Communication
Conformational effect on fluorescence emission of
tetraphenylethylene-based metallacycles
b
c
Zhewen Guoa, Jun Zhaoa, Yuhang Liua, Guangfeng Lia, , Heng Wang , Yali Hou ,
*
Mingming Zhangc, Xiaopeng Lib, Xuzhou Yana,
*
a
School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai 200240, China
b
College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518055, China
c
State Key Laboratory for Mechanical Behavior of Materials, Shaanxi International Research Center for Soft Matter, School of Materials Science and Engineering,
Xi’an Jiaotong University, Xi’an 710049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 6 October 2020
Received in revised form 8 December 2020
Accepted 14 December 2020
Available online 19 December 2020
Herein, we designed and constructed two metallacycles,1 and 2, to illustrate the conformational effect of
isomeric AIE fluorophores on the platform of supramolecular coordination complexes (SCCs). Specifically,
the dangling phenyl rings in TPE units of the metallacycle 1 align completely outside the main cyclic
structure, while in the metallacycle 2, these phenyl rings align half inside and half outside. The
experimental results showed that two metallacycles exhibited different behaviors in terms of AIE
fluorescence and chemical sensing, which could be attributed to the subtle structural difference of the
TPE units. This work represents the unification of topics such as self-assembly, AIE, and chemical sensing,
and further promotes the understanding for the structure-property relationship of isomeric AIE
fluorophores.
Keywords:
Conformational effect
Structure-property relationship
Aggregation-induced emission
Coordination-driven self-assembly
Metallacycles
© 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
In recent years, fluorescent materials are undergoing acceler-
ated and sustained growth. They have gained considerable
attention due to widespread applications in environmental
sensing, bioimaging, lighting devices and so on [1–4]. However,
traditional fluorophores only work well in dilute conditions.
The fluorescence would quench abruptly if they accumulate in the
condensed phase, which is known as the frustrating aggregation-
caused quenching (ACQ) phenomenon [5,6]. This troublesome
problem was subtly tackled when Tang et al. reported an entirely
opposite phenomenon called aggregation-induced emission (AIE)
[7,8]. In this case, some typical chromophores emit faintly in dilute
solutions but intensively in concentrated solutions. Such brand-
new properties could be attributed to the restriction of intramo-
lecular rotation and vibration of chromophores in the aggregated
state. These AIE-active fluorogens bridged the gaps in traditional
luminous materials, thus driving a huge bulk of researches [9–12].
Although sophisticated structures and delicate design of AIE
molecules/assemblies have been reported [13–15], the relationship
between the conformation of AIE units and the resulting photo-
physical properties has rarely been studied.
Supramolecular coordination complexes (SCCs), prepared by
means of coordination-driven self-assembly, provide a suitable
platform for further study of AIE chemistry [16,17]. Discrete
metallacycle, a certain type of SCCs, can be efficiently achieved
through self-assembly of ligands and central metals via labile
coordination bonds. Were the angularities, directionalities, and
stoichiometries defined, these building blocks would then
contribute to the assumed exquisite structures through reversible
bonds efficiently [18–21]. Owing to their controllable structures
and properties, the detailed structure-property relationship of AIE
moieties could be explored at the (supra)molecular level.
Tetraphenylethylene (TPE) group is one of the most frequently
used AIE units due to its facile synthesis and excellent stability
[22,23]. Its original free rotation of phenyl rings and double bond
could be restricted in the aggregated state, thus leading to the
emission of fluorescence. After being fabricated by pyridine
groups, TPE ligands could be implanted in the SCC systems. In
recent years, we have reported the construction of light-emitting
metal-organic materials on the SCC platforms and then investi-
gated the influence on their AIE performance in terms of shapes,
counter anion, number of chromophores and so on [24].
However, the relationship between the fine structure of AIE
units and the corresponding fluorescence remains unsettled. It is
plausible that any fine modulation may bring about a profound
* Corresponding authors.
1001-8417/© 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.