Quantum size titanium oxide templated with a π-conjugated dendrimer: crystal structure in the quantum size domain

Metal-based nanoparticles templated with dendrimers have recently attracted much interest to control particle sizes strictly. However, the standard deviation of the obtained particles is larger than that of the single-mass Au clusters (0.2 nm). We succeeded the subnanosize-control of TiO2 particles (both of rutile and anatase crystal structures based on the difference in the synthesis methods) with a standard deviation of 0.2 nm, using finely controlled metal assembly on a phenylazomethine dendrimer (DPA G4). The optical absorption spectra of the obtained particles revealed that the quantum size effect and the difference in the crystal structure, such as rutile and anatase, exists less than 2 nm particle sizes. A semi-empirical effective mass approximation, introduced a new concept; apparent reduced mass, describes the size dependency and the difference based on the crystal structure in the bandgap energy of the indirect and direct transition.