Charge transfer in hybrid organic-inorganic PbS nanocrystal systems

Charge transfer interactions between PbS nanocrystals (NCs) and tetrathiafulvalene (TTF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) are studied using optical spectroscopy. Selective quenching of PbS NC photoluminescence (PL) by TTF is observed and related to the relative alignment of the highest occupied molecular orbital (HOMO) of TTF and the PbS NC 1s(h) energy level. TCNQ is also found to quench PbS NC PL irrespective of the NC bandgap. A ground-state charge transfer mechanism between PbS and TCNQ is proposed to account for the observed quenching indirectly supported by observed changes in the absorption spectra of PbS-TTF and PbS-TCNQ solutions. Additionally, a second emission band in the visible spectral region ( approximately 675 nm) is found upon excitation of PbS-TCNQ solutions. These results are of interest for the future design of charge-transfer systems for use in hybrid organic-inorganic systems.