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

Abstract

Here, we discuss self-assembled multicomponent organic/inorganic nanostructures. Self-assembled multiporphyrin triads were formed via non-covalent interactions of meso-phenyl bridged ZnOEP chemical dimer, (ZnOEP) 2 Ph, with dipyridyl substituted tetrapyrrole extra-ligand. In tetrads, the dimer (ZnOEP) 2 Ph is covalently linked via 5-mesoposition to additional electron acceptors (quinone Q, pyromellitimide Pim). Using steady-state, time-resolved fluorescent and pump-probe results, main relaxation pathways have been elucidated: competing energy migration and photoinduced electron transfer (PET) in normal triads within ≤1.4 ps; very fast (within ∼700 fs) PET in porphyrin triads containing pentafluorinated porphyrin remaining still efficient at 77-120 K; a bridge-dimer mediated long-range (r DA =18-24 Å) superexchange PET "extra-ligand→Q or Pim" in tetrads. Self-assembly of nanostructures from semiconductor CdSе/ ZnS quantum dots (QD) and tetra-meso-pyridyl-substituted porphyrins is also based on extra-ligation interactions and results in a strong quenching of QD photoluminescence (PL). At the same molar ratios x =[H 2 P(m-Pyr) 4 ]/[QD], the quenching is more effective for small QDs than for larger ones. From experimental Stern-Volmer PL quenching plots I 0 /I(x) and the quantum mechanical calculations for the electron wave functions it follows that the specificity of the exciton non-radiative decay in "QD-porphyrin" nanocomposites is due to the manifestation of inductive and mesomeric effects leading to the charge tunnelling through ZnS barrier in quantum confinement conditions.

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

“…Like in the case of multiporphyrin complexes, [15,18,20,39,40] the selective replacement of meso-phenyl rings in tetra-phenyl porphyrins by pyridyl rings, H 2 P(Pyr) n as well as CuP(Pyr) 4 , offers the possibility for a controllable formation of "QD-Porphyrin" nanocomposites via a coordination "key-hole" principle. [20,46,48,49] It is well-known from chemical background that the 3d transition metal Zn 2+ ion has empty 3d 10 orbital while heteroatom N-pyr of the porphyrin meso-pyridyl ring is a very good e-donor having an unshared electron pair.…”

“…[20,46,48,49] It is well-known from chemical background that the 3d transition metal Zn 2+ ion has empty 3d 10 orbital while heteroatom N-pyr of the porphyrin meso-pyridyl ring is a very good e-donor having an unshared electron pair. Correspondingly, in this case a "key-hole" Formation of "Semiconductor Quantum Dots -Porphyrin" Nanocomposites principle is realized via one-or two-fold non-covalent coordination Zn ….…”

“…[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.…”

“…[10,11] In the organic world, the preparation of supramolecular architectures in which organic compounds present a high degree of order, which spans from the nanoscopic to the macroscopic level across multiple length scales, is highly desirable and represents a key issue within the fast-growing fields of nanoscience and nanotechnology. [12][13][14][15][16][17][18][19][20] In this respect, the interest in emerging organic nanostructures formed via the bottom-up approach (including those based on tetrapyrrolic macrocycles) is growing exponentially since they are not only good models for mimicking the primary photochemical processes in vivo but seem to be considered as promising building blocks for advanced multifunctional nanocomposites with potential applications in improved drug delivery systems, photodynamic therapy, nanovoltaic cells, optoelectronic memory, multimolecular architectures for information storage and highly efficient catalysts. [21][22][23][24][25][26] However, many fundamental issues still need to be in-depth investigated in order to have full understanding of mechanisms that drive the properties of organic nanocomposites.…”

Synthesis and Properties of meso-Tetraphenylporphyrins with Sulfhydryl Groups

“…[16] Furthermore, the structure and physicochemical properties of porphyrins will determine the functional properties of the resulting conjugates. [17] Despite the broad abilities that thiolcontaining porphyrins may open while forming the novel hybryd materials, the synthesis of these porphyrin is associated with certain difficulties. This work is focused on design of novel thiolcontaining tetraphenylporphyrins and study of their photosensitizing activity in model reaction of anthracene oxidation.…”