Linn Wagnert - Academia.edu (original) (raw)

Papers by Linn Wagnert

The Journal of Physical Chemistry a, Jul 1, 2008

The photoexcited states of two 5,10,15-tris(pentafluorophenyl)corroles (tpfc), hosting Rh(III) in... more The photoexcited states of two 5,10,15-tris(pentafluorophenyl)corroles (tpfc), hosting Rh(III) in their core, namely Rh(pyr)(PPh 3 )(tpfc) and Rh(PPh 3 )(tpfc), have been studied by time-resolved electron paramagnetic resonance (TREPR) combined with pulsed laser excitation. Using the transient nutation technique, the spin polarized spectra are assigned to photoexcited triplet states. The spectral widths observed for the two Rh(III) corroles crucially depend on the axial ligands at the Rh(III) metal ion. In case of Rh(PPh 3 )(tpfc), the TREPR spectra are found to extend over 200 mT, which exceeds the spectral width of non-transition-metal corroles by more than a factor of 3. Moreover, the EPR lines of the Rh(III) corroles are less symmetric than those of the non-transition-metal corrroles. The peculiarities in the TREPR spectra of the Rh(III) corroles can be rationalized in terms of strong spin-orbit coupling (SOC) associated with the transition-metal character of the Rh(III) ion. It is assumed that SOC in the photoexcited Rh(III) corroles effectively admixes metal centered 3 dd-states to the corrole centered 3 ππ*-states detected in the TREPR experiments. This admixture leads to an increased zero-field splitting and a large g-tensor anisotropy as manifested by the excited Rh(III) corroles.

Chemical & Engineering News, 1969

The Journal of Physical Chemistry B, 2010

The effect of the corrole macrocycle bromination on its photoexcited triplet state parameters was... more The effect of the corrole macrocycle bromination on its photoexcited triplet state parameters was examined in a comparison study of brominated and nonbrominated Ga(III) 5,10,15-tris(pentafluorophenyl)corroles, employing X-band (9.5 GHz) time-resolved electron paramagnetic resonance (TREPR) spectroscopy. It is demonstrated that the spectrum of the brominated Ga-corrole is characterized by an opposite polarization pattern and a larger zero-field splitting (ZFS) parameter |D|, compared to nonbrominated Ga-corrole. With the assignment of a negative sign for the ZFS parameter D, the dominant intersystem crossing (ISC) pathways are evaluated. Spectral line shape analysis reveals that in the brominated Ga-corrole,the out-of-plane triplet sublevel is overpopulated (A Z > A X , A Y ), while in nonbrominated Ga-corrole, the in-plane triplet sublevels are preferentially populated (A X , A Y . A Z ). The differences in the photophysical properties of the corroles are attributed to the heavy atom effect upon corrole skeleton bromination, which enhances the spin-orbit coupling strength in the brominated complex, thus affecting its ISC and ZFS parameters. † Part of the "Michael R. Wasielewski Festschrift".

The Journal of Physical Chemistry A, 2005

The magnetic field dependence of electron spin polarization (ESP), generated in free radicals whe... more The magnetic field dependence of electron spin polarization (ESP), generated in free radicals when they encounter photoexcited triplets, was measured experimentally and analyzed theoretically. The time-resolved electron paramagnetic resonance measurements were performed with a microwave setup consisting of lowloss dielectric ring resonators with tunable microwave frequencies and the corresponding magnetic fields. The ESP of the radical was found in the magnetic field range of 170-370 mT, and the results of the calculation based on the numerical solution of the stochastic Liouville equation were found to be in line with the experimental data showing that ESP decreases when the magnetic field increases.

The Journal of Physical Chemistry A, 2008

The Journal of Physical Chemistry A, 2012

We combine femtosecond polarization resolved VIS-pump IR-probe spectroscopy with DFT and TD-DFT c... more We combine femtosecond polarization resolved VIS-pump IR-probe spectroscopy with DFT and TD-DFT calculations to identify and assign absorption bands to electronic transitions for corroles. These macrocycles and their corresponding metal complexes are receiving great attention because of their utility in many fields, while many of their spectroscopic features have not yet been fully described. Analysis of the perturbed free induction decay provides information about the bleaching signal at time zero and allows for determination of overlapping excited state and bleaching signal amplitudes. The S(0) → S(1) and S(0) → S(2) transitions in the Q-band of the hexacoordinated Al(tpfc)(py)(2) and Br(8)Al(tpfc)(py)(2) absorption spectra are explicitly assigned. Angles between these electronic transition dipole moments (tdms) with a single vibrational transition dipole moment of (53 ± 2)° and (34 ± 2)° when excited at 580 and 620 nm for hexacoordinated Al(tpfc)(py)(2) and (51 ± 2)° and (43 ± 2)° when excited at 590 and 640 nm for hexacoordinated Br(8)Al(tpfc)(py)(2) were determined. The relative angles between the two lowest electronic tdms are (90 ± 8)° and (94 ± 3)° for Al(tpfc)(py)(2) and Br(8)Al(tpfc)(py)(2), respectively. Angles are determined before time zero by polarization resolved perturbed free induction decay and after time zero by polarization resolved transients. Comparison of corrole&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s wave functions with those of porphine show that the reduced symmetry in the corrole molecules results in lifting of Q-band degeneracy and major reorientation of the electronic transition dipole moments within the molecular scaffold. This information is necessary in designing optimal corrole-based electron and energy transfer complexes.

Journal of Porphyrins and Phthalocyanines, 2007

ABSTRACT Three photosensitizers based on tris-(pentafluorophenyl)antimony corroles that differ in... more ABSTRACT Three photosensitizers based on tris-(pentafluorophenyl)antimony corroles that differ in oxidation state and axial ligands, namely, (pyridine)Sb(III)-, (oxo)Sb(V)- and (difluoro)Sb(V) complexes, were studied by time-resolved electron paramagnetic resonance spectroscopy and laser flash photolysis. The magnetic and orientational parameters of the corroles oriented in a nematic liquid crystal as well as their triplet lifetimes in liquid toluene were determined and interpreted in terms of their structure and geometry. The negative zero-field splitting parameter D assigned to all studied corroles is explained by the asymmetric π-electron withdrawal effect caused by perfluorinated peripheral aryl groups, which force the triplet electron spins to align in head-to-tail configuration. The effect of the axial ligands on the photoexcited triplet state properties of the corroles is correlated with their different efficiency to perform photoassisted aerobic oxygenation of some organic molecules. This is explained by the dependence of the main parameters of the photoexcited complexes on the interaction between the central ion and corrole π-system. This interaction is strongly influenced by axial ligands coordination, affecting the macrocycle symmetry, planarity, and rigidity.

Applied Magnetic Resonance, 2006

The photoexcited triplet states of three 5,10,15-tris(pentafluorophenyl)corroles (tpfc), hosting ... more The photoexcited triplet states of three 5,10,15-tris(pentafluorophenyl)corroles (tpfc), hosting Sn(IV) and AI(III) in their core, namely, Sn(Cl)(tpfc), Al(pyr)2(tpfc ) and Al(pyr)2(tpfc-Brs), were studied by time-resolved electron paramagnetic resonance (TREPR) spectroscopy in the nematic liquid crystal E7. Only two of these metallocorroles, namely, Sn(C1)(tpfc) and Al(pyr)2(tpfc-Br8), exhibit TREPR spectra following pulsed laser excitation. This result is rationalized in terms of a very low quantum yield of triplet formation in Al(pyr)2(tpfc ). Analysis of the spin polarized Q-band (34 GHz) EPR spectra of Sn(Cl)(tpfc) and Al(pyr)2(tpfc-Brs) provides detailed information on the magnetic and kinetic parameters of the triplet states as well as on the molecular ordering of the complexes in the liquid crystal. With the assignment of the zero-field splitting parameter D < 0 for the Sn(C1)(tpfc) and Al(pyr)2(tpfc-Brs), one can evaluate the dominant intersystem crossing path for these metallocorroles. Analysis reveals that in Sn(C1)(tpfc) the in-plane triplet sublevels are preferentially populated, i.e., A x, A r >> A z. This can be rationalized in terms of weak electronic interactions between the Sn(IV) ion and the corrole n-system, consistent with the domed structure of Sn(Cl)(tpfc). In Al(pyr)2(tpfc-Brs), however, the out-of-plane triplet sublevel is predominantly populated, i.e., A z > A x, Ar, which is attributed to a large increase in the spin-orbit coupling strength arising from the peripheral bromine atoms on the corrole skeleton.