The combination of multiple functional molecules is of great importance for the creation ofhybrid nanomaterials with new desired functions. Among functional materials, colloidal
semiconductor nanocrystals, so-called quantum dots (QDs), have attracted much attention
because of their outstanding photoluminescence properties, such as a high photodurability,sharp PL spectra. Therefore, the emission and optoelectronic properties in the dispersed
conditions have been actively studied. In addition, understanding the physical properties derived
from inter-QD interactions observed in the solid condition of QDs is quite important for thedevelopment of QD-based materials science. However, the individual QDs are unsuitable forself-assembly in solution due to the high dispersibility in organic solvents. Therefore, theconstruction of assembled structures composed of multiple QDs is still challenging (Review:
self-assembly of QDs, Ref 26, Chem. Eur. J., 2020, 26 ,7176).
In contrast, the self-assembly of organic -conjugated molecules is a powerful tool to create
various extended nanostructures, such as nanofibers and nanosheets (Ref 16, Chem. Eur. J.,
2017, 23, 5270). When this prominent self-assembly is applied to the QD system, indirect QD
self-assembly can be realized. Recently, we proposed a new strategy to form supramolecular
structures of QDs by using the self-assembly of low molecular weight organic molecules (Ref20, Chem. Eur. J., 2019, 25, 167). Furthermore, we succeeded in the construction of highlyordered QD arrangement structures and their photocontrol (Ref 31, Angew. Chem. Int.
Ed., 2021, in press, attached paper).
1) QD arrangement based on self-assembly of PBI
First, we selected a perylene bisimide (PBI) dye with adhesion moieties to CdSe QDs as theself-assembling molecule, and conducted the mixing of QD and PBI in non-polar solvents.
Upon mixing, QD and PBI coaggregate into a unique nanostructure composed of arranged QDs
along a two-dimensional (2D) sheet of PBI, as confirmed by transmission electron microscopy(TEM) observation. To obtain insight into the mechanism of QD-PBI coaggregate formation,
we studied the kinetics of time-dependent coaggregation using UV/vis absorption spectroscopy
and TEM observation. From the in-depth analysis, the QD-PBI mixture just after mixing formed
an amorphous coaggregate without QD arrangement through a strong face-to-face (H-type) stacking between PBI. After one hour, the amorphous aggregates transformed into the welldefined coaggregates with QD arrangement via the rearrangement of stacking style of PBI.
2) Photocontrol over highly ordered QD supramolecular structures
The use of photochromic molecules such as azobenzene is an essential strategy for the creationof photoresponsive materials (Ref 8, Nature Commun., 2015, 6: 8936; Ref 23, Angew. Chem.
Int. Ed., 2019, 58, 14173). In order to realize a photoresponsive QD system, we synthesized anazobenzene derivative (Azo) with an adhesion moiety to CdSe QDs and attempted thecoaggregation of QD and Azo in non-polar solvents. As a result, we succeeded in the formationof highly ordered hybrid structures with QD arrangement, in which the energy transfer between
QDs occurs effectively. Furthermore, upon photoirradiation, the highly ordered structuretransferred into ill-defined coaggregates showing a lower efficiency of energy transfer, which isbased on the photoisomerization of Azo. Over one day, the irradiated coaggregates underwent
recovery of the PL properties corresponding to the arranged QDs through thermal isomerization.