Circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS quantum dots (QDs) and chlorin e6 (Ce6) molecules in dimethyl sulfoxide (DMSO) and in aqueous solutions at different pH levels were investigated. The changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. CD spectroscopy allowed us to obtain the CD spectrum of a luminescent Ce6 dimer and to identify a nonluminescent Ce6 aggregate, which is thought to be a tetramer. The dissymmetry factor of the tetramer is 40 times larger than that of the Ce6 monomer. The analysis of the obtained data showed that in complexes with QDs Ce6 can be either in the monomer form or in the form of a nonluminescent tetramer. The interaction of the relatively unstable luminescent Ce6 dimer with QDs leads to its partial monomerization and the formation of complexes with Ce6 in the monomer form. On the basis of time-dependent density functional theory calculations, we performed a geometry model of Ce6 dimer form with corresponding calculated absorption and CD spectra, which are in a qualitative agreement with the experimental data.
Here we report our investigations of the formation conditions and photophysical properties of complexes between luminescent semiconducting nanoparticles (quantum dots, QDs) and the photosensitizer chlorin e6, which is widely used for the photodynamic therapy. In our complexes, bovine serum albumin (BSA), the most abundant protein in blood serum, was used as a linker between QDs and chlorin e6 molecules. The influence of BSA on the optical properties of Ce6 and QDs in complexes was properly examined using spectral-luminescent methods. It was found that BSA passivated QD surface and substantially QD quantum yield of luminescence was increased. In addition, BSA prevented the aggregation of chlorin e6 molecules in complexes with QDs. We demonstrated that the use of BSA as a linker allows to create functional QD-chlorin e6 complexes with effective photoexcitation energy transfer from QDs to the molecules.
Experimental investigation of circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS QDs
and chlorin e6 (Ce6) molecules in aqua solutions at different pH level, in methanol and in DMSO were carried out. The
changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. Application of CD
spectroscopy allowed to obtain the CD spectrum of luminescent Ce6 dimer for the first time, and to discover a nonluminescent
Ce6 aggregate, preliminary identified as a "tetramer", dissymmetry factor of which is 40 times larger than
that for its monomer. The analysis of obtained data showed that in complexes with QDs Ce6 can be either in the
monomeric form or in the form of non-luminescent tetramer. The interaction of relatively unstable luminescent Ce6
dimerwith QDs leads to its partial monomerization and formation complexes with chlorin e6 in monomeric form.