Hole Transfer Dynamics from a CdSe/CdS Quantum Rod to a Tethered Ferrocene Derivative

Hole transfer between a CdSe/CdS core/shell semiconductor nanorod and a surface-ligated alkyl ferrocene is investigated by a combination of ab initio quantum chemistry calculations and electrochemical and time-resolved photoluminescence measurements. The calculated driving force for hole transfer corresponds well with electrochemical measurements of nanorods partially ligated by 6-ferrocenylhexanethiolate. The calculations and the experiments suggest that single step hole transfer from the valence band to ferrocene is in the Marcus inverted region. Additionally, time-resolved photoluminescence data suggest that two-step hole transfer to ferrocene mediated by a deep trap state is unlikely. However, the calculations also suggest that shallow surface states of the CdS shell could play a significant role in mediating hole transfer as long as their energies are close enough to the nanorod highest occupied molecular orbital energy. Regardless of the detailed mechanism of hole transfer, our results suggest that holes may be extracted more efficiently from well-passivated nanocrystals by reducing the energetic driving force for hole transfer, thus minimizing energetic losses

Effect of Thermal Fluctuations on the Radiative Rate in Core/Shell Quantum Dots

The effect of lattice fluctuations and electronic excitations on the radiative rate is demonstrated in CdSe/CdS core/shell spherical quantum dots (QDs). Using a combination of time-resolved photoluminescence spectroscopy and atomistic simulations, we show that lattice fluctuations can change the radiative rate over the temperature range from 78 to 300 K. We posit that the presence of the core/shell interface plays a significant role in dictating this behavior. We show that the other major factor that underpins the change in radiative rate with temperature is the presence of higher energy states corresponding to electron excitation into the shell. These effects should be present in other core/shell samples and should also affect other excited state rates, such as the rate of Auger recombination or the rate of charge transfer

Formation Principles for Templated Vanadium Selenite Oxalates

A set of formation principles governing organically templated vanadium selenite oxalates are described in the context of nine new compounds. The compositions of the reaction mixture dictate the form of the secondary building units from which [(VO)₂­(C₂O₄)­(SeO₃)₂]_<i>n</i>^2<i>n</i>– layers are constructed. The strength of hydrogen-bonding interactions is maximized in these compounds, directly affecting the orientations of the organic ammonium cations and enabling amine packing efficiency to affect layer tessellation. The orientations of selenite stereoactive lone pairs are driven by the minimization of internal void space. Compound symmetry can be directed to chiral space groups through the use of chiral components, with the use of either (<i>R</i>)-2-methylpiperazine or (<i>S</i>)-2-methylpiperazine, resulting in noncentrosymmetric, polar, chiral structures that crystallize in the space group <i>P</i>2₁ (No. 4)

Formation Principles for Templated Vanadium Selenite Oxalates

A set of formation principles governing organically templated vanadium selenite oxalates are described in the context of nine new compounds. The compositions of the reaction mixture dictate the form of the secondary building units from which [(VO)₂­(C₂O₄)­(SeO₃)₂]_<i>n</i>^2<i>n</i>– layers are constructed. The strength of hydrogen-bonding interactions is maximized in these compounds, directly affecting the orientations of the organic ammonium cations and enabling amine packing efficiency to affect layer tessellation. The orientations of selenite stereoactive lone pairs are driven by the minimization of internal void space. Compound symmetry can be directed to chiral space groups through the use of chiral components, with the use of either (<i>R</i>)-2-methylpiperazine or (<i>S</i>)-2-methylpiperazine, resulting in noncentrosymmetric, polar, chiral structures that crystallize in the space group <i>P</i>2₁ (No. 4)