Liquid-Crystalline Organic-Inorganic Hybrid Dendrimer with aCdS
Nano-Core: Photoluminescence Behavior of the Self-Organized Assembly
Kiyoshi Kanie,1,* Masaki Matsubara,1 Jun Yabuki,1Masafumi Nakaya,1
Xiangbing Zeng,2 Warren Stevenson,2Goran Ungar,2 Atsushi Muramatsu1
1 Institute of Multidisciplinary Research for Advanced Material, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
2 Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK
Semiconductor quantum dots (QDs) have attracted a great deal of attention in material science due to their size-dependent and tuneable absorption and emission properties. In addition, periodic arraysof QDs have a considerable potential in applicationsinnovel nano-electronic and optical devices. Recently, we developed liquid-crystalline (LC) organic-inorganic hybrid dendrimers,1 where the dendrimer has a spherical gold nanoparticle (NP) atitscore.Dense surface modification of spherical gold NPs with LC
G2dendronmoleculeswas found to result in a hybrid exhibiting a thermotropic LC phase with simple cubic structure. The chemical structure of G2 is shown in Figure 1. In the present study we focus on imparting such ability to self-organizeonto monodisperse QD nanospheres. As a result, dendron-modified QDs were obtained, displaying ordered superlattices. Such structures were found to exhibitunusual photoluminescence (PL) behaviour.
As the internal core of the dendrimer,CdS NPs C1-C3with different degrees of CO2H modification amountwasprepared. Surface modification of C1-C3 by G2 was carried out by amidation reaction. Average particle size of core part ofC1, C2, and C3 were calculated as 3.9, 3.9, and 3.8 nm, respectively.
Figure 2 shows TEM images of C1 NPs andG2 modified C1 (G2/C1).The interparticle distance of G2/C1 expanded into ca. 9 nm after modification with G2. The numbers of G2 moleculesper one particle for G2/C1, G2/C2, and G2/C3 were assigned as 69, 54, and 47 molecules, respectively, from TG analysis. SAXS and DSC measurements showed that G2/C1 exhibited thermotropic LC phases in a wide range of temperatures. At 150 °C, G2/C1 formed a thermotropiccubic LC phase with a novel structure.The cubic structure was retained at room temperature after cooling. On the other hand, only randomstructure was seen for G2/C2 and G2/C3.The G2/C1dendrimer as deposited on a glass substrate,also formed a disorderedstructure . In such a state, itshowed strong photoluminescence when UV irradiated at 365 nm (Figure 3a). However the PLwas quenchedwhen the G2/C1dendrimerself-organized in the cubic phase after annealing at 150 °Cfollowed by cooling (Figure 3b). Such PL quenchingbehaviour was totally reversible, and appears tobe derived from the periodic structure of G2/C1. The detailed analysis on PL quenching is now in progress.Such unusual PL behavior might be a powerful tool to develop future functional devices.
[1] K. Kanie, M. Matsubara, X. Zeng, F. Liu, G. Ungar, H. Nakamura, A. Muramatsu,J. Am. Chem. Soc.134, 808 (2012).
* presenting author; E-mail: