## 3 Results and Discussions
### Growth Mechanism of TiO\({}_{2}\) Nanocrystals
The abovementioned reaction route is described in Equations (1)-(3):  
\[\rm{Ti}\Big{(}O^{\rm i}Pr\Big{)}_{4}\ +\ xC_{17}H_{33}COOH\ \rightarrow\ \big{(}C_{17}H_{33}COOH\big{)}_{x}-Ti\Big{(}O^{\rm i}Pr\Big{)}_{4-x}\ +\ xPrOH \tag{1}\]  
\[\rm{PrOH}\ +\ C_{17}H_{33}COOH\ \rightarrow\ C_{17}H_{33}COOH\ +\ H_{2}O \tag{2}\]  
\[\rm{(C_{17}H_{33}COO)}_{x}-Ti\Big{(}O^{\rm i}Pr\Big{)}_{4-x}\ +\ H_{2}O\ \rightarrow\ \big{(}C_{17}H_{33}COOH\big{)}_{x}\Big{(}O^{\rm i}Pr\Big{)}_{3-x}TiO \ +\ xPrOH\]  
\[\rm{(C_{17}H_{33}COO)}_{x}\Big{(}O^{\rm i}Pr\Big{)}_{3-x}TiO \ +\ \big{(}C_{17}H_{33}COOH\big{)}_{x}\Big{(}O^{\rm i}Pr\Big{)}_{3-x}TiO\]  
\[\rm{\rightarrow(C_{17}H_{33}COO)}_{x}\Big{(}O^{\rm i}Pr\Big{)}_{3-x}Ti-\!O\!- \!Ti\big{(}C_{17}H_{33}COOH\big{)}_{x}\Big{(}O^{\rm i}Pr\Big{)}_{3-x}\ +\ H_{2}O\]  
Although we think that the hydrolysis followed by condensation is the main route of oxide formation, the possibility of a nonhydrolytic condensation of titanium carboxylate complex to form **Ti\(-\)O\(-\)Ti** bonds cannot be ruled out, either [20]. It is known that an oxo bridge can be formed by a condensation reaction between two functional groups bonded to two metal centers (here titanium atoms) along with eliminating an organic ester molecule [46]. Thus, after the formation of the titanium carboxylate complex, also a transesterification can occur between the complex and TTIP precursor to generate the Ti\(-\)**O\(-\)Ti** bonds and eliminate an ester. These reaction steps are shown in Equations (4) and (5):  
\[\rm{Ti}\Big{(}O^{\rm i}Pr\Big{)}_{4}\ +\ \big{(}C_{17}H_{33}COOH\big{)}_{x}-Ti \Big{(}O^{\rm i}Pr\Big{)}_{4-x}\ \rightarrow\ \big{(}C_{17}H_{33}COOH\big{)}_{x}-\ \big{(}O^{\rm i}Pr\Big{)}_{4-x}Ti-\!O\!-\!Ti\big{(}O^{\rm i}Pr\big{)}_{3}\ +\ \big{(}C_{17}H_{33}COOH \big{)} \tag{4}\]  
\[\rm{n(C_{17}H_{33}COO)}_{x}-Ti\Big{(}O^{\rm i}Pr\Big{)}_{4-x}\ \rightarrow\ \ \rm{n}/_{2}\ \bigg{[}\Big{(}O^{\rm i}Pr\Big{)}_{3-x}Ti-\!O\!-\!Ti\big{(}C_{17}H_{33}COOH \big{)}_{x-1}\bigg{]}\ +\ \rm{n}/_{2}\ \big{(}C_{17}H_{33}COOH\big{)} \tag{5}\]  
[PERSON] et al. suggested that these molecular species were enclosing a compact **Ti\(-\)O\(-\)Ti** framework of hexa-coordinated Ti atoms and could be regarded as titania monomers protected by carboxylate ligands. In these monomers, OLAC molecules have a tendency to bridge titanium centers [20]. Therefore, we surmise that titania NCs synthesized in our experiment might have been formed via both hydrolytic-condensation and nonhydrolytic-condensation routes, but it is not clear to what extent each path contributed. In Figure 2, we monitored the progressive evolution of TiO\({}_{2}\) NCs by extracting aliquots of the hot reaction mixture at scheduled time intervals. These hot extractions were swiftly cooled down to room temperature via quenching in toluene to stop further crystal growth. Interestingly, ultrathin TiO\({}_{2}\) NRs (1.8 \(\pm\) 0.3 nm (thickness) and 36.4 \(\pm\) 10.1 nm (length)) were produced in the early stages of the reaction (first 10 min). These ultrathin NRs were of the anatase polymorph. This relatively fast formation of the titania NRs was also reported in the literature for the case of Ti(OBu)\({}_{4}\) decomposed in a pure OLAC medium leading to anatase NRs in less than 15 min [47]. In each panel of Figure 2, the length distribution of TiO\({}_{2}\) is shown as a histogram. In addition to the length distributions, we can observe that the ultrathin TiO\({}_{2}\) NRs became thicker over time from 1.8 \(\pm\) 0.3 nm to 3.6 \(\pm\) 0.4 nm. Moreover, in the first 10 min of the experiment, ultrathin NRs had a broad length distribution of 36.4 \(\pm\) 10.1 nm. After 10 more minutes, shorter but thicker NRs of 21.8 \(\pm\) 2.8 nm were mostly detected in the reaction mixture, which then increased in both thickness and length, finally resulting in nanorods with a broad length distribution of 27.6 \(\pm\) 6.9 nm and a collection of semispherical NCs.