Surface Photochemistry of Quantum Dot-Porphyrin Nanoassemblies for Singlet Oxygen Generation

Abstract

This Chapter covers the basics of nanotechnology, focusing on hybrid organic-inorganic nanoassemblies based on self-assembly principles. Here, we are willing to discuss the formation principles and mechanisms of excitation energy relaxation being studied for nanoassemblies based on core/shell CdSe(ZnS) colloidal semiconductor quantum dots (QD) exhibiting size-dependent photophysical properties and surfacely activated by pyridyl-substituted porphyrins, H 2 P (bulk solutions) in liquid solvents at 295 K (steady-state, picosecond time-resolved luminescence spectroscopy and single molecule spectroscopy). Upon formation of QD-H 2 P nanoassemblies the QD photoluminescence (PL) is quenched as can be detected both via single particle detection and ensemble experiments in solution. PL quenching has been quantitatively assigned to FRET QD→ H 2 P (10-14%) and Non-FRET (86-90%) processes. Using near-IR photoluminescence measurements, we performed a quantitative comparative studying the efficiencies of the singlet oxygen generation by alone QDs and "QD-H 2 P" nanoassemblies upon variation of the laser pulse energy. It was found that for QD-H 2 P nanoassemblies the experimental efficiencies of singlet oxygen generation are essentially higher with respect to those obtained for alone QDs. In the case of QD-H 2 P nanoassemblies, it was proven also that the non-linear dependence of the efficiency of singlet oxygen generation on the laser pulse energy is caused by non-radiative intraband Auger processes, realized in QD counterpart. It has been found that values of FRET QD→ H 2 P efficiencies obtained via direct measurements of IR-emission of singlet oxygen at low laser excitation (Φ IR = 0.12 ± 0.03) are in a good agreement with the corresponding FRET efficiencies found from the direct sensitization data for porphyrin fluorescence (Φ FRET = 0.14 ± 0.02) in nanoassemblies. Such quantitative analysis was done for the first time and shows that namely FRET process QD→H 2 P is a main reason of singlet oxygen generation by QD→H 2 P nanoassemblies.

Organic–Inorganic Hybrid Nanosystems for Photodynamic Therapy

“…At first glance all these data are consistent with highly efficient Förster resonant energy transfer (FRET) from QDs to MB molecules which supposed to be main mechanism of enhancing photodynamic properties of various photosensitizers using this approach. [6][7][8] However, upon the inspection of extends of PL quenching and reduction of PL lifetime we have concluded that, for this system, photoinduced charge transfer is the most likely mechanism of PL quenching. The evidence for the photoinduction can be derived through the comparison of lifetime and PL intensity Stern-Volmer plots, which shows orders of magnitude difference (Figure 2d).…”

Deactivation of Excited States in Nanostructures Containing Cu-Porphyrin Subunit

“…In this case, like for multiporphyrin complexes (described above), a controllable formation of "QD-Porphyrin" nanoassemblies have been realized as a surface passivation of CdSe/ZnS ODs by tetrameso-pyridyl substituted porphyrins (free base and/or Cu-complex) in titration experiments. [29,[90][91][92][93][94][95][96][97][98][99] It is well-known from chemical background that the 3d transition metal Zn 2+ ion (of ZnS shell) has empty 3d 10 orbital while heteroatom N-pyr of the porphyrin mesopyridyl ring is a very good e-donor having an unshared electron pair. Thus, in this case a "key-lock" principle is realized via oneor two-fold non-covalent coordination Zn….N-pyr.…”

“…[29,[90][91][92][93][94][95][96][97][98][99]123] Structures of QDs and porphyrin molecules as well as necessary details explaining the formation of nanoassemblies "QD-Porphyrin" are shown in Figure 9. The results described below concern to the analysis of the interaction between semiconductor CdSe/ZnS quantum dots and surface attached porphyrin molecules (free base and Cu-complex) in order to evaluate the influence of tetrapyrrolic macrocycle on pathways and mechanisms of exciton relaxation in "QD -Cu-porphyrin" nanoassemblies.…”

“…and nanobiophotonics (nanoprobes for biomedical imaging, biosensing and photodynamic therapy of cancer, etc). [23][24][25][26][27][28][29][30][31][32] In this respect, the 2014 Nobel Prize in chemistry (E. Betzig, S.W. Hell and W.E.…”