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Sun et al. Chem Synth 2023;3:16 https://dx.doi.org/10.20517/cs.2022.45 Page 3 of 17

Scheme 1. Schematic illustration of the advantages of host-guest assemblies in photothermal therapy, with cyclodextrin, cucurbituril,
and pillararene as representative hosts and aniline tetramer (TANI), camptothecin (CPT) as representative guests.

exposure [33,34] according to American National Standard for Safe Use of Lasers. Hence, the construction of
photothermal agents that function in NIR-II range is of significant importance for the development of
photothermal therapy as well. Host-guest interaction provides a unique microenvironment [35,36] , which may
induce the redshift of the UV-Vis-NIR absorption of guest molecules. In addition, the occurrence of host-
guest interaction for surface-modified nanomaterials can cause variation in their supramolecular
morphology , which, to some degree, facilitates the manipulation of photothermal conversion efficiency
[37]
both in NIR-I and NIR-II range. In this section, the enhancement of photothermal efficiency of
photothermal agents promoted by host-guest interaction is exemplified and the underlying principles are
clarified.

Host-guest interaction-induced enhancement of photothermal conversion efficiency in NIR-I
For host-guest assembly, the inner cavity of the macrocyclic host can provide a unique microenvironment
for guest molecules, which, in some cases, can induce the enhancement of the photothermal conversion
efficiency of the guest. ICG is a well-known NIR-I absorptive reagent. Because of its excellent
biocompatibility, it is widely applied in photothermal therapy [38,39] . However, in aqueous solution, ICG is
easily aggregated , which will decrease its photothermal conversion efficiency. Moreover, upon laser
[40]
[41]
irradiation, ICG can undertake decomposition, which further attenuates its photothermal capability . To
overcome these problems, Ding et al. prepared quaternary ammonium cations-modified water-soluble
[42]
pillar[5]arene (WP5) [Figure 1A] . Through hydrophobic and electrostatic interaction, ICG can be