jp505986c_si_001.pdf (3.59 MB)
Electronic and Vibrational Structure of Complexes of Tetracyanoquinodimethane with Cadmium Chalcogenide Quantum Dots
journal contribution
posted on 2014-08-07, 00:00 authored by Laura
C. Cass, Nathaniel K. Swenson, Emily A. WeissThis paper describes the use of visible, near-infrared, and mid-infrared
steady-state optical spectroscopy to study the geometries in which
tetracyanoquinodimethane (TCNQ) adsorbs to the surfaces of highly
cadmium enriched and near-stoichiometric CdSe quantum dots (QDs) in
the formation of QD-TCNQ charge transfer (CT) complexes. Several TCNQ
molecules are spontaneously reduced by chalcogenides on the surface
of each CdSe QD. The degree of CT depends on the geometry with which
the TCNQ adsorbs and the degree of distortion of TCNQ’s geometry
upon adsorption. Comparison of the electronic and vibrational spectra
of CdSe QD-TCNQ complexes with those of CT complexes of TCNQ with
molecular reductants (including molecular chalcogenides) and computer
simulations of the geometries and vibrational spectra of the TCNQ-chalcogenide
CT complexes show that (i) the Cd-enriched CdSe QDs reduce a factor
of 7.4 more TCNQ molecules per QD than nearly stoichiometric CdSe
QDs because surface selenides are more accessible in the Cd-enriched
QDs than in the near-stoichiometric QDs and (ii) TCNQ interacts with
surface selenides through several adsorption modes that result in
different amounts of charge transfer and different degrees of geometric
distortion of TCNQ. This study provides a framework for determining
the range of adsorption geometries of small molecules on QD surfaces,
and for optimizing QD surfaces to adsorb molecules in configurations
with maximal electronic coupling between the QD and the adsorbate.