Competition between electron transfer and energy migration in self-assembled porphyrin triads

Abstract

Ž .Ž . The photoinduced electron transfer ET and the energy migration EM processes have been studied in liquid solutions and polymeric Ž . Ž . PMMA films for the triads consisting of the Zn-octaethylporphyrin chemical dimer the energy and electron donor, D and dipyridyl Ž . substituted tetrapyrrole extra-ligands porphyrins, chlorin, tetrahydroporphyrin as the acceptors, A. On the basis of the time correlated single photon counting technique and femtosecond pump-probe spectroscopy, it has been shown that D fluorescence quenching with time constant ranging from 1.7 to 10 ps is due to competing EM and ET processes from the dimer to A's. In addition, the fluorescence decay Ž . time shortening by ; 1.3-1.6 times in toluene at 293 K is observed for electron accepting extra-ligands in the triads. The acceptor fluorescence quenching is hard dependent on the mutual spatial arrangement of the triad subunits, but becomes stronger upon the solvent Ž . Ž . polarity increase addition of acetone to toluene solutions as well as the temperature lowering from 278 to 221 K . The possible reasons and mechanisms of the non-radiative deactivation of locally excited S -states in the triads are discussed taking into account a close lying 1 charge-separated state. The obtained experimental data are analyzed using the reduced density matrix formalism in the frame of Haken-Strobl-Reineker approach. This model includes EM and ET processes as well as the dephasing of coherence between the excited electronic states of the triad. q

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

“…Clear understanding of the energy transfer mechanisms and pathways involved in this two-step process is essential to the design of effective PDT drugs. The pathway taken by the photoexcitation in the QD-dye nanoassembly is best described with the modern theory of energy transfer, which is greatly motivated by search for novel energy sources, design of artificial light-harvesting systems, and understanding the efficient light harvesting seen in nature [32][33][34][35][36][37][38]. The energy and electron transfer processes in the light-harvesting systems are driven by the ultrafast photoinduced evolution of the electronic degrees of freedom, which are strongly affected by the dynamic reorganization of the quantized vibrational modes [39][40][41].…”

“…An intermediate description between the rate theories and molecular dynamics is provided by the reduced density matrix methods [38,[41][42][43][62][63][64], which couple several explicit electronic or vibrational modes to a thermal bath of many modes.…”

Multistep photoinduced electron transfer in self-organised nanoscale porphyrin triads

“…It is worth noting that a small but noticeable shortening of uorescence decays was detected for the same extra-ligands in triads without A's that was attributed to a photoinduced hole transfer from the extra-ligand to the dimer [11]. Experimental data collected in the Table show also that for the triads of the same geometry but having extra-ligands of various nature the extra-ligand uorescence decay shortening decreases in the following sequence: 2 .…”

“…2). The detailed analysis of femtosecond spectral-kinetic data (presented in our forthcoming papers [11,12]) shows that the formation of charge transfer (CT) states could be appropriately detected, and the primary fast deactivation of the locally excited S 1 -states of interacting subunits (the dimer and extra-ligand) is caused by the competition between the energy migration and sequential electron=hole transfer.…”

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

“…[27][28][29][30] Correspondingly, based on ideas of the self-assembly discussed above, the combination of the two directions, that is the anchoring of functional organic molecules (including tetrapyrrolic compounds and other heteromacrocycles) or molecular complexes or even proteins to QDs, is of considerable scientific and a wide practical interest including material science and biomedical applications. [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).…”