| 1. |
- Zenkevich, Eduard I, et al.
(författare)
-
Quantitative Analysis of Singlet Oxygen ((1)O(2)) Generation via Energy Transfer in Nanocomposites Based on Semiconductor Quantum Dots and Porphyrin Ligands
- 2011
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 115:44, s. 21535-21545
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the results of a detailed quantitative experimental exciton relaxation pathways as well as direct measurement of singlet oxygen ((1)O(2)) generation efficiencies for CdSe/ZnS quantum dot (QD)- porphyrin nanocomposites in toluene at 295 K QD photoluminescence. quenching in nanocomposites is caused. by two main factors: electron tunneling in the quantum confined QD.(efficiency 0.85-0.90) and Forster resonance energy transfer (FRET) QD -andgt; porphyrin (quenching efficiency 0.10-0.15). Efficiencies of (1)O(2) generation gamma(Delta) by nanocomposites are essentially higher with respect to those obtained for QDs alone. For nanocomposites, the nonlinear decrease of (1)O(2) generation efficiency gamma(Delta) on the laser pulse energy is caused by nonradiative intraband Auger processes, realized in the QD counterpart. Finally, FRET efficiencies found from the direct sensitization data for porphyrin fluorescence in, nanocomposites (Phi(FRET) = 0.14 +/- 0.02) are in good agreement with the corresponding values obtained via the direct (1)O(2) generation measurements at low laser excitation (Phi(Delta)(FRET) = 0.12 +/- 0.03). The obtained quantitative results provide for the first time strong evidence that a FRET process QD -andgt; porphyrin is the reason for singlet oxygen generation by nanocomposites.
|
|
| 2. |
|
|
| 3. |
- Blaudeck, Thomas, et al.
(författare)
-
Biocomputation Using Molecular Agents Moving in Microfluidic Channel Networks : An Alternative Platform for Information Technology
- 2022
-
Ingår i: Cyber-Physical Systems : Intelligent Models and Algorithms - Intelligent Models and Algorithms. - Cham : Springer International Publishing. - 2198-4190 .- 2198-4182. - 9783030951153 - 9783030951160 ; 417, s. 15-27
-
Bokkapitel (refereegranskat)abstract
- Deficiencies in software or computer chips cause computers or smartphones to crash and allow hackers to steal passwords. Automated test procedures could avoid these problems. However, the computing power and cooling requirements of conventional computers increase exponentially with the size of the problem, so that the technological limits for solving these problems will soon be reached. The EU project Bio4Comp aims to develop concepts for a bio-computer to help overcome these two main problems. Compared to conventional computers, computers based on biological molecular motors only consume a fraction of the energy per arithmetic operation and scale very well for problems that can be parallelized (“multitasking”). In this article, the topic network-based biocomputation (NBC) i.e. computing with biological molecules as agents that are driven by molecular motors in microfluidic networks, is presented as an alternative approach to computing, data processing, and information technology.
|
|
| 4. |
- Blaudeck, Thomas, et al.
(författare)
-
Formation Principles and Ligand Dynamics of Nanoassemblies of CdSe Quantum Dots and Functionalised Dye Molecules
- 2012
-
Ingår i: ChemPhysChem. - : Wiley-Blackwell / Wiley-VCH Verlag Berlin. - 1439-4235 .- 1439-7641. ; 13:4, s. 959-972
-
Tidskriftsartikel (refereegranskat)abstract
- Functional dye molecules, such as porphyrins, attached to CdSe quantum dots (QDs) through anchoring meso-pyridyl substituents, form quasi-stable nanoassemblies. This fact results in photoluminescence (PL) quenching of the QDs both due to Forster resonance energy transfer (FRET) and the formation of non-radiative surface states under conditions of quantum confinement (non-FRET). The formation process is in competition with the ligand dynamics. At least two timescales are found for the formation of the assemblies: 1) one faster than 60 s attributed to saturation of empty attachment sites and 2) one slower than 600 s, which is attributed to a reorganisation of the tri-n-octylphosphine oxide (TOPO) ligand shell. Finally, this process results in almost complete exchange of the TOPO shell by porphyrin dye molecules. Following a SternVolmer analysis, we established a microscopic description of PL quenching and assembly formation. Based on this formalism, we determined the equilibrium constant for assembly formation between QDs and the pyridyl-functionalised dye molecules to be K approximate to 10(5)-10(7) M-1, which is several orders of magnitude larger than that of the TOPO ligands. Our results give additional insights into the non-FRET PL quenching processes involved and show that the QD surface is inhomogeneous with respect to the involved attachment and detachment processes. In comparison with other methods, such as NMR spectroscopy, the advantage of our approach is that ligand dynamics can be investigated at extremely low ratios of dye molecules to QDs.
|
|
| 5. |
- Zenkevich,, Eduard I., et al.
(författare)
-
Size-Dependent Non-FRET Photoluminescence Quenching in Nanocomposites Based on Semiconductor Quantum Dots CdSe/ZnS and Functionalized Porphyrin Ligands
- 2012
-
Ingår i: International Journal of Spectroscopy. - : Hindawi Publishing Corporation. - 1687-9449 .- 1687-9457. ; 2012:971791
-
Tidskriftsartikel (refereegranskat)abstract
- We review recent experimental work to utilize the size dependence of the luminescence quenching of colloidal semiconductor quantum dots induced by functionalized porphyrin molecules attached to the surface to describe a photoluminescence (PL) quenching process which is different from usual models of charge transfer (CT) or Foerster resonant energy transfer (FRET). Steady-state and picosecond time-resolved measurements were carried out for nanocomposites based on colloidal CdSe/ZnS and CdSe quantum dots (QDs) of various sizes and surfacely attached tetra-mesopyridyl-substituted porphyrin molecules (“Quantum Dot-Porphyrin” nanocomposites), in toluene at 295 K. It was found that the major part of the observed strong quenching of QD PL in “QD-Porphyrin” nanocomposites can neither be assigned to FRET nor to photoinduced charge transfer between the QD and the chromophore. This PL quenching depends on QD size and shell and is stronger for smaller quantum dots: QD PL quenching rate constants scale inversely with the QD diameter. Based on the comparison of experimental data and quantum mechanical calculations, it has been concluded that QD PL quenching in “QD-Porphyrin” nanocomposites can be understood in terms of a tunneling of the electron (of the excited electron-hole pair) followed by a (self-) localization of the electron or formation of trap states. The major contribution to PL quenching is found to be proportional to the calculated quantum-confined exciton wave function at the QD surface. Our findings highlight that single functionalized molecules can be considered as one of the probes for the complex interface physics and dynamics of colloidal semiconductor QD.
|
|
