# Interface Engineering Strategies for Fabricating Nanocrystal-Based Organic-Inorganic Nanocomposites
## 2 Overview of Ligand Exchange
### Organic-Inorganic Hybrid Nanocomposites
synthesized CdSe NCs in the presence of P3 HT by utilizing the steric hindrance from the side chains of P3 HT, yielding a simple mixture of CdSe/P3 HT [67]. A binary solvent (i.e., octadecene (ODE) and 1,2,3-trichlorobenzene (TCB)) was used to dissolve both cadmium precursors (i.e., dimethylcadmium) and P3 HT. Subsequently, selenium precursors in trioctylphosphine were injected into the solution to initiate nucleation and growth. [PERSON] et al. reported on an in situ growth process of anisotropic CdS NCs in a P3 HT matrix [27]. A polar solvent, dimethyl sulfoxide (DMSO), was used to dissolve the cadmium precursors, cadmium acetate, and 1,2-dichlorobenzene (DCB) was employed to dissolve P3 HT. Similarly, injection of sulfur precursors resulted in intimate contact in the CdS NC/P3 HT nanocomposites. Intriguingly, the shape of the NCs evolved from a spherical dot to an NR-like morphology with increasing cadmium precursor concentration. A growth mechanism for the formation of NRs was proposed: CdS NRs were grown along the P3 HT backbone upon the anchoring of cadmium cations (Cd\({}^{2+}\)) on the S atoms of P3 HT, as schematically illustrated in Figure 8[27]. This is elucidated by FTIR measurements, where the signal corresponding to the S-C stretching of P3 HT shifted after the addition of cadmium acetate into P3 HT, suggesting the formation of intermolecular interactions at the expense of the S-C bond energy. Figure 7: Schematic illustration of ligand exchange and grafting of end-functionalized CPs onto NCs. Reprinted with permission from [24]. Copyright 2007 American Chemical Society. However, such direct growth approaches often result in dangling bonds on the surface, which can act as charge trapping sites. A binary solvent was required to dissolve both metal precursors and polymers (e.g., DCB for P3 HT and DSMO for cadmium acetate). Moreover, the resulting CPs/NCs mixture may suffer from poor colloidal stability, resulting in agglomeration of NCs in the polymer matrix because CPs are not chemically tethered onto the NC surface [27; 68]. In this respect, an advanced in situ technique to form CP-grafted NCs (i.e., P3 HT-CdSe NC nanocomposites) by capitalizing on judiciously designed CP-grafted metal precursors (i.e., Cd-P3 HT complexes) was introduced by [PERSON] et al. (Figure 9) [23]. Specifically, CP-grafted precursors (i.e., Cd-P3 HT complexes) were first synthesized via a click reaction between ethynyl-terminated P3 HT and N\({}_{3}\)-functionalized Cd-phosphonic acid complexes (i.e., Cd-BPA-N\({}_{3}\)). Finally, a hot injection of selenium precursors into the Cd-P3 HT solution yielded intimately contacted P3 HT-grafted CdSe NCs. The formation of dangling bonds (e.g., Cd\({}^{2+}\) and Se\({}^{2-}\)), which is unavoidable in the aforementioned conventional in situ growth techniques [27; 68], can be greatly reduced when P3 HT-grafted Cd complexes are employed. Furthermore, the morphology of the NCs can be controlled to form QDs or tetrapods by precisely tuning the ratio of cadmium precursors to Cd-P3 HT [23]. Figure 8: Schematic illustration of the growth mechanism of CdS NCs in the presence of P3 HT. Reprinted with permission from [27]. Copyright 2009, American Chemical Society. Figure 9: Formation of P3 HT-CdSe QD nanocomposites via in situ growth. Reprinted with permission from [23]. Copyright 2016, Royal Society of Chemistry. A novel synthetic route to form organic-inorganic hybrid nanocomposites using block copolymer nanoreactors (i.e., templates) to guide direct in situ growth of NCs with precisely controlled dimensions, compositions, and architectures was introduced by [PERSON]'s group [69; 70; 71]. The synthesized NCs were permanently linked to the CPs, imparting long-term stability of the resulting CP-grafted NC hybrid nanocomposites in various organic solvents. An amphiphilic diblock copolymer, composed of inner hydrophilic and outer hydrophobic blocks, was synthesized from a \(\beta\)-cyclodextrintrin core.