Singlet oxygen

Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O (also written as 1[O2] or 1O2), which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambient temperature, but the rate of decay is slow. The lowest excited state of the diatomic oxygen molecule is a singlet state. It is a gas with physical properties differing only subtly from those of the more prevalent triplet ground state of O2. In terms of its chemical reactivity, however, singlet oxygen is far more reactive toward organic compounds. It is responsible for the photodegradation of many materials but can be put to constructive use in preparative organic chemistry and photodynamic therapy. Trace amounts of singlet oxygen are found in the upper atmosphere and also in polluted urban atmospheres where it contributes to the formation of lung-damaging nitrogen dioxide. It often appears and coexists confounded in environments

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Photochemical and photophysical properties of diketopyrrolopyrrole organic pigments

Various aspects of the pigment class based on 1,4-diketo-3,6-diphenyl-pyrrolo(3,4-c)pyrrole (DPP) are investigated. The thesis consists of two parts: the first part, motivated by the degradation problems of DPP, focuses on the molecular photophysics of the DPP class of compounds. The second part, motivated by photovoltaic applications, focuses on the electrical and photovoltaic properties of solid state DPP. Investigation of the photoluminescence of the main commercial derivative, p-Cl DPP (PCD) showed, that the emission of the pigment in polymer matrices may be attributed to aggregates at the surface and that it is sensitized by monomers of DPP. From the distinct excitation spectrum of the monomers it is thus concluded that these play a major role in the photoactivity and photodegradation of the pigments. In solution the dominant role of singlet oxygen in the degradation of the molecule has been shown. The quenching of the singlet excited state of DPP by oxygen efficiently produces singlet oxygen and triplet States of DPP. The latter is again an efficient sensitizer of singlet oxygen. The triplet state energy has been measured for DPP (28.5±2 kcal/mol) and the p-dimethylamino derivative DMADPP (29.5±2 kcal/mol). The triplet energy for DMADPP is slightly higher than for DPP, although the respective singlet energies have the opposite trend (DPP: 56 kcal/mol and DMADPP: 51 kcal/mol). Based on molecular orbital calculations this observation is attributed to the structure of the HOMO and LUMO orbitals and it is concluded that the large singlet to triplet energy splitting is a property of the core of the pyrrolopyrrole chromophore. DPP and DTPP (dithioketo-DPP) are used in electrochemical and heterojunction solid state photovoltaic cells based on porous TiO2 electrodes. MCDPP, a derivative of DPP using a carboxylic anchoring group yielded an incident photon to current conversion efficiency of 47% in a photoelectrochemical cell. The solid state photovoltaic cells yielded poor photocurrents. The use of MCDPP in the TiO2/DPP heterojunction increased the photocurrent. Surface photovoltage spectroscopy and Kelvin probe measurements were used to determine the workfunction of DPP (5.38 eV), DTPP (4.95 eV) and DMADPP (5.08 eV) and to investigate surface and interface band bendings of DTPP on SnO2. A band diagram is proposed for this system. DTPP and DPP showed both p-type band bending.

EPFL1997

Temperature and oxygen-concentration dependence of singlet oxygen production by RuPhen as induced by quasi-continuous excitation

Veronika Huntosova, Jaroslav Varchola, Georges Wagnières

Advanced Search Home > Journals > Photochemical & Photobi... > Temperature and oxygen-... For Authors & Referees | For Librarians | For Members Journal cover: Photochemical & Photobiological Sciences Photochemical & Photobiological Sciences Issue 12, 2014 A society-owned journal publishing high quality research on all aspects of photochemistry and photobiology. Impact Factor 2.939 12 Issues per Year Indexed in Medline Journal Home Previous Article | Next Article Paper Temperature and oxygen-concentration dependence of singlet oxygen production by RuPhen as induced by quasi-continuous excitation Jaroslav Varchola,a Veronika Huntosova,b Daniel Jancura,ab Georges Wagnières,c Pavol Miskovskyab and Gregor Bánó*ab Show Affiliations Photochem. Photobiol. Sci., 2014,13, 1781-1787 DOI: 10.1039/C4PP00202D Received 06 Jun 2014, Accepted 02 Oct 2014 First published online 06 Oct 2014 | | Share on citeulike | Share on facebook | Share on twitter | | More PDF Rich HTML Send PDF to Kindle Download Citation Help Request Permissions Abstract Cited by Related Content Assessment of partial pressure of oxygen (pO2) by luminescence lifetime measurements of ruthenium coordination complexes has been studied intensively during the last few decades. RuPhen (dichlorotris(1,10-phenanthroline) ruthenium(II) hydrate) is a water soluble molecule that has been tested previously for in vivo pO2 detection. In this work we intended to shed light on the production of singlet oxygen by RuPhen. The quantum yield of singlet oxygen production by RuPhen dissolved in 0.9% aqueous NaCl solution (pH = 6) was measured at physiological temperatures (285–310 K) and various concentrations of molecular oxygen. In order to minimize the bleaching of RuPhen, the samples were excited with low power (

2014

Kinetic modeling of lag times during photo-induced inactivation of E. coli in sunlit surface waters: Unraveling the pathways of exogenous action

Stefanos Giannakis, César Pulgarin, Jean Arnaud Troyon

This work presents a kinetic analysis of the exogenous photo-induced disinfection of E. coli in natural waters. Herein, the inactivation of bacteria by light and photo-generated transient species, i.e., hydroxyl radical (HO center dot), excited triplet states of organic matter ((CDOM)-C-3*) and singlet oxygen (O-1(2)), was studied. It was found that the exogenous disinfection of E. coli proceeds through a lag time, followed by an exponential phase triggered by photo-generated HO center dot, O-1(2) and (CDOM)-C-3*. Also, we report that the concentration increased of transient species (and especially HO center dot) precursors decreased the lag times of bacteria inactivation. Due to the limitations of the competition kinetics methodology to include the lag phase, an alternative strategy to study the interaction between E. coli and photo-generated transient species was proposed, considering the log-linear pseudo-first order rate constants and lag-times. On this basis and by using APEX software, a full kinetic analysis of exogenous bacterial inactivation, taking into account both lag-time and exponential decay, was developed. This approach provided insights into the conditions that could make exogenous inactivation competitive with the endogenous process for the E. coli inactivation in natural sunlit waters. Hence, this research contributes to the understanding of fundamental kinetic aspects of photoinduced bacterial inactivation, which is the basis for light-assisted processes such as the solar disinfection (SODIS). (C) 2019 Elsevier Ltd. All rights reserved.

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