PHOTOINDUCED RELAXATION PROCESSES IN COMPOSITES BASED ON SEMICONDUCTOR NANOCRYSTALS CdSe AND ORGANIC LIGANDS

Photoinduced Relaxation Processes in Self-Assembled Nanostructures: Multiporphyrin Complexes and Composites “CdSе/ZnS Quantum Dot-Porphyrin”

“…Nevertheless, fluorescence parameters (efficiency ϕ F and decay τ) for H 2 P(m-Pyr) 4 molecules upon complexation with QDs remain the same practically with respect to those measured for individual ligands and the same conditions. [19,53] In addition, the comparative titrations of the same QD solutions by H 2 P(m-Pyr) 4 and THP(m-Pyr) 4 (holes acceptor) ligands as well as by H 2 P(m^Pyr) 2 (Ph) 2 and electron acceptors, H 2 P(m^Pyr) 2 (5FPh) 2 or H 2 P(m^Pyr) 2 (Anthraquinone) 2 , gives the same curves for QD photoluminescence quenching. [19,53] Thus, non-dependence of QD PL quenching efficiency on redox properties of porphyrin ligands and the absence of the porphyrin fluorescence quenching in "QD-porphyrin" composites rules out the dominant role of usual photoinduced charge transfer processes with participation of molecular orbitals of porphyrin macrocycle in QD PL quenching for the systems under study.…”

“…[19,52] Firstly, it has been definitely shown that the porphyrin fluorescence enhancement is of order of 10% being much smaller as compared to the corresponding photoluminescence remains nearly the same. [20,53] So, the contribution of EM QD→porphyrin to the total PL quenching seems to be minor and hence is negligible in most cases. Taking into account the results discussed in previous sections, one should conclude that in the case of the photoinduced charge (hole or electron) transfer processes in "QD-porphyrin" composites the porphyrin ligand fluorescence should be also diminished.…”

“…Data presented in Table 3 show that for CdSe/ZnS quantum dots with two ZnS monolayers k q values follow a monotonous function drastically decaying with the QD core diameter. From the physico-chemical point of view, we conjecture that upon interaction of H 2 P(m-Pyr) 4 molecule with QD surface, the electron wave function may be locally modified (via inductive and/or mesomeric effects [53] ) forming a surface local state capable to trap the electron of the photogenerated exciton. The general scheme of our model is shown in Figure 13A.…”

Block copolymer containing poly(3‐hexylthiophene) and poly(4‐vinylpyridine): Synthesis and its interaction with CdSe quantum dots for hybrid organic applications

“…The fluorescence intensity of the pyridine modified CdSe, however, decreased by nearly a factor of six, providing an indirect evidence for the ligand exchange process. Pyridine has been shown to quench the fluorescence of the quantum dots through the coordination with cadmium 15. UV–vis solution spectra of P3HT‐P4VP diblock copolymer and a blend of 1:1 (by weight) CdSe and P3HT‐P4VP are shown in Figure 3.…”

Ligand Exchange Dynamics and Temperature Effects upon Formation of Nanocomposites Based on Semiconductor CdSе/ZnS Quantum Dots and Porphyrins: Ensemble and Single Object Measurements

“…[31][32][33][34][35][36][37][38] Inspired by our earlier work on self-assembled multiporphyrin arrays [39][40][41][42][43][44][45] we have elaborated the experimental approach in the direct labelling of trioctylphosphine oxide (TOPO)-and amino (AM) -capped semiconductor quantum dots (QD) CdSe/ZnS with functional ligands (dyes) of two types (pyridyl substituted porphyrins and heterocyclic pyridyl functionalized perylene diimide molecules) in liquid solutions and polymeric matrixes. [46][47][48][49][50][51][52][53][54][55] We have shown that depending on redox and electronic properties of interacting subunits as well as anchoring groups (connecting organic and inorganic counterparts) the formation of "QD-Dye" nanocomposites allows for a controlled realization of mutually relative (spatial) orientations and electronic energy scales in order to optimize intended photoinduced processes such as charge transfer, [56,57] fluorescence Foerster energy transfer (FRET) [20,46,47,50,52] or electron tunnelling in the conditions of quantum confinement (non-FRET process). [48,50,53] Typically, all these processes lead to the pronounced quenching of QD photoluminescence (PL) in nanocomposites that may be used as an indicator of complex interface phenomena selectively depending on attached ligands (porphyrins, perylene diimides, etc.…”