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Lee et al. Microstructures 2023;3:2023021 https://dx.doi.org/10.20517/microstructures.2023.08 Page 9 of 19

Recently, covalent organic frameworks have emerged as a promising alternative for encapsulating CQDs in
microporous structures, offering advantages such as high stability, excellent control over pore size and
shape, and the ability to tune the chemical and physical properties of the framework for specific
applications. The presence of a large number of conjugated structures for both CQDs and COFs enables a
unique opportunity to engineer their interfacial properties. Generally, CQDs have a size between 3 and
5 nm, which can be considered as a big molecular block within a typical COFs structure. Chen et al. formed,
for the first time, two COFs consisting of carbon quantum dots which were generated through the Schiff
base reactions with CQDs and phenylenediamine (pPDA) and BODIPY with two amino groups, as shown
in Figure 5 . In this study, solvothermal methods were utilised to synthesise spherical CQDs with a size of
[69]
ca. 5 nm. The synthesised CQDs were then dispersed in ethyl alcohol along with pPDA
(p-phenylenediamine), and in a mixed solvent of ethyl alcohol and acetic acid with BODIPY, to form novel
types of carbon dot-based covalent organic frameworks (CCOFs).

These newly synthesised CCOFs exhibit a bulk, spherical nanoparticle morphology, ranging in size from
200 to 500 nanometres. These structures are composed of carbon quantum dots, which are covalently
bonded to organic ligands. Subsequently, the surfaces of these CCOFs are modified with polyethylene glycol
(PEG) to further enhance their stability and dispersibility in aqueous environments. Following
modification, the composite demonstrates no signs of aggregation for up to 24 h when exposed to a 10%
fetal bovine serum (FBS) solution in water. By contrast, unmodified CCOFs exhibit aggregation under the
same conditions. In addition, blood compatibility was evaluated by administering a dose of 10 mg/kg of
modified CCOFs to mice, demonstrating no adverse effects on biosafety at that concentration. Furthermore,
under green LED laser irradiation, the composite exhibited marked inhibition of tumour growth and size
reduction. This carbon quantum dot-based covalent organic framework exhibits highly desirable
characteristics, including excellent physiological stability, biocompatibility, and remarkable reactivity in
[69]
oxygen generation, positioning them as a promising contender for cancer treatment .
QUANTUM DOTS IN METAL-ORGANIC FRAMEWORKS
Compared to zeolites and COFs, MOFs are a highly versatile family of microporous materials with a hybrid
organic-inorganic continuous porous structure. They are formed by the coordination of metal ions with
organic ligands, creating a three-dimensional network of pores and channels with high surface area and
tunable properties. This material was introduced by Tomic in 1965 as a porous coordination framework.
More than 80,000 types of MOFs have been reported so far, due to the wide selection of metal ions and
organic ligands used to form a structure [Figure 6] [70-73] . The presence of inorganic and organic coordination
is a distinguishing factor of MOFs compared to covalent organic COFs, which are composed solely of light
organic elements such as carbon, nitrogen, hydrogen, boron, and oxygen. High surface area, uniform
structure, flexible choice of metal and organic ligands, structure tunability, and chemical functionality make
this material unique and ideal for various applications such as separation, catalysis, sensing, and as a
protective host matrix. One of the most extensively studied topics in the field of MOFs is hybrid
nanocomposite materials. Due to the strong coordination between metal nodes and organic ligands, MOFs
exhibit good chemical resistance to a wide range of solvents, including polar, nonpolar, and apolar solvents.
Furthermore, porous structures can be tailored to a given requirement. These advantageous characteristics
make this material a strong candidate as the protective host matrix for hybrid nanocomposites [74-77] .

Organic-inorganic metal halide perovskites have been a trending subject in material science as a
semiconducting light-harvesting material for various applications due to their outstanding properties, such
as high light absorption coefficient, high defect tolerances and long charge carrier diffusion distances [78,79] .
However, relatively low stability to moisture, heat and most common polar solvents limits the applicable