Triplet state | EPFL Graph Search

In quantum mechanics, a triplet state, or spin triplet, is the quantum state of an object such as an electron, atom, or molecule, having a quantum spin S = 1. It has three allowed values of the spin's projection along a given axis mS = −1, 0, or +1, giving the name "triplet". Spin, in the context of quantum mechanics, is not a mechanical rotation but a more abstract concept that characterizes a particle's intrinsic angular momentum. It is particularly important for systems at atomic length scales, such as individual atoms, protons, or electrons. A triplet state occurs in cases where the spins of two unpaired electrons, each having spin s = 1/2, align to give S = 1, in contrast to the more common case of two electrons aligning oppositely to give S = 0, a spin singlet. Most molecules encountered in daily life exist in a singlet state because all of their electrons are paired, but molecular oxygen is an exception. At room temperature, O2 exists in a triplet state, which can only underg

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

This work deals with the engineering of a new luminescent complex of lanthanide, able to be specifically grafted onto biological materials and to emit a characteristic light useful in quantifying the concentration of the target molecules. We have based our molecular design on TbL1, wich possesses a significant quantum yield in water pointing to an efficient intramolecular energy transfer. We have elaborated the synthesis of a ligand derived from L1 and named L3, by functionalizing one of the chromophoric groups into a moiety able to couple the luminescent sensor to biological materials. The synthesis of the complexes was then realized. The thermodynamic study of the ligands L1 and L3, and their terbium complexes in water was made to establish the distribution diagrams and to compare their behaviour, especially at neutral pH. In addition, EuL1 was also investigated and the complexation constants of TbL1, EuL1 and TbL3 in water showed that these molecules are thermodynamically stable in aqueous media. Characterization of EuL3 in the solid state by high resolution luminescence allowed us to determine the geometry of the coordination sphere of the Eu(III) ion, which possesses a distorded C4 symmetry. The detailed study of the Eu(III) ion transitions evidenced two different sites, possibly arising from an equilibrium induced by the competition between a water molecule and the carboxylate function. This interpretation is in line with the measured lifetimes of the Tb(III) and Eu(III) excited states and the calculation of the hydration number of the complexes in aqueous solution. The determination of the energy of the singlet state and triplet states of the ligand, as well as of the emitting levels of the Ln(III) ions in solution showed that their relative values are favorable for a good intramolecular energy transfer. The quantum yields of TbL3 and EuL3, which amount to 2.6 % and 1.4 %, respectively, are lower than those of the complexes with L1, denoting that the presence of the acid function increases losses in the energy transfer. However, these values remain sizeable enough for potential biomedical applications. The study of the intermolecular energy transfer from EuL1, EuL3 and TbL3 to the acceptor Cy5 has proved promising, and the resulting yields were 90 % for EuL1 and 80 % for the complexes with L3.

EPFL2004

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

Photochemical and photophysical properties of diketopyrrolopyrrole organic pigments

EPFL1997

Complexes luminescents de lanthanides avec des dérivés du cyclène comme briques pour l'ingénierie de sondes analytiques biomédicales

EPFL2004