Self-Assembled Multilayers of CdSe Nanocrystals and Hydrazine or Linear Diamines

Hydrazine and two linear diamines, H2N-(CH2)n-NH2 (n = 2 and 6), were reacted with (hexadecylamine/stearate)-capped CdSe nanoparticles (7.5 nm diameter) to form multilayers on ITO glass via layer-by-layer alternation. The new materials were investigated by cyclic voltammetry (CV), UV-vis and FTIR spectroscopies, and photoconductivity. FTIR analysis of multilayer growth showed the complete removal of both L (hexadecylamine) and X (stearate) caps; the latter occurred via complexation of the external cadmium layer. Bulk CdSe/hydrazine polymer, obtained from treatment of a CdSe nanocrystal (CdSe-NC) dispersion with excess hydrazine, included massive amounts of hydrazine in a N2H4/CdSe molar ratio of approximately 24. On the contrary, CV analysis showed that hydrazine covers the NC surface of multilayers with approximately 2x10-9 mol cm-2; specifically, the N2H4/CdSe molar ratio was much lower (ca. 0.5). FTIR analysis of bulk CdSe/diamine polymers showed the same NC surface coverage, (1-2)X10-9 mol cm-2, of the CdSe/hydrazine multilayers. The shortest hydrazine linker results in the highest photocurrent values. Diamines display lower photoconductivity values, decreasing as the N-N distance is increased.