Conspectus
In recent
years, purely organic
room-temperature phosphorescence
(RTP) has aroused wide concern and promotes the development of the
supramolecular phosphorescence. Different from organic crystallization,
polymerization, or matrix rigidification, supramolecular strategy
mainly takes advantage of the synergy between supramolecular co-assembly
and strong binding by macrocyclic host compounds (cucurbit[n]urils,
cyclodextrins, etc.) to overcome deficiencies such as poor processability
and water solubility and improves RTP materials’ quantum efficiency
and lifetime in the solid state or in an aqueous solution. Meanwhile,
it expands application, especially in aqueous solution, in cell imaging.
Therefore, supramolecular phosphorescence will become a new growth
point and will have broad application prospects in chemistry, biology,
and material science.
This Account focuses on the uniquely synergetic
advantages of co-assembly
and host–guest interaction from macrocyclic hosts for enhancing
RTP. This Account starts with a brief introduction of the recent development
of organic RTP materials as well as the host–guest interaction
and co-assembly. Then, we introduce a supramolecular solid-state RTP
strategy involving an ultrahigh phosphorescent quantum yield via the
tight encapsulation of macrocyclic host cucurbit[6]uril, an ultralong
lifetime via changing the substituents of phosphors, and long-lived
and bright RTP by the synergy of host–guest interaction and
polymerization. Meanwhile, the applications of solid-state RTP materials
for anti-counterfeiting and data encryption are presented. The third
part will be the water-phase supramolecular phosphorescence systems
constructed by water-soluble macrocyclic host cucurbit[8]uril. Host–guest
interaction and polymerization worked together toward efficient phosphorescence
in aqueous solution, and the multi-stage assembly promoted phosphorescent
applications such as cell targeted imaging and energy transfer. A
humidity sensor and data encryption by the conversion of supramolecular
hydrogels and xerogels are also involved. In the summary section,
we present perspectives and possible research directions for supramolecular
phosphorescence.
Furthermore, on the basis of previous research,
we would like to
conclude and propose the developing concept of “macrocycles
enhance guest’s phosphorescence”, and this concept not
only means that the macrocyclic host limits the movement of the guest
compound or promotes interactions between guest compounds but also
involves the synergetic enhancement centered on macrocyclic compounds
via multi-stage supramolecular assembly which further improves the
efficiency of RTP, water solubility, and biocompatibility. And we
believe that this concept will be able, together with theory of “assembly-induced
emission” and “aggregation-induced emission”,
to accelerate the development of purely organic RTP materials.