XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
270
T4: P–3
Magnetic circular dichroism of cyclic and linear porphyrin oligomers
Patrycja Kowalska
1
, Martin Peeks
2
, Harry L. Anderson
2
,
and Jacek Waluk
1
1
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw,
Poland, e-mail: pkowalska@ichf.edu.pl
2
Department of Chemistry, Oxford University, 12 Mansfield Rd, Oxford OX1 3TA, UK
Growing interest in novel molecular electronic devices accelerates the development and
extensive studies of new materials. Particularly attractive in this respect are -conjugated
oligoporphyrin systems synthesized in Oxford [1]. Potential applications of such species are
determined by their electronic structure. In this work, we compare the electronic structures of
cyclic and linear porphyrin oligomers, using electronic absorption and magnetic circular
dichroism (MCD) spectroscopy combined with quantum chemical calculations. We demonstrate
the advantages of MCD not only for spectral assignments, but, especially, for detecting
ultraweak electron currents in a cyclic, templated oligomer c-P6T6. Contrary to the absorption,
MCD spectra of c-P6T6 differ drastically from those of a non-templated cyclic oligomer, c-P6,
as well as from the spectra of linear oligomers consisting of two (P2), four (P4) and six (P6)
monomeric subunits. The observation of the Faraday A term in c-P6T6 allows estimating the
value of the magnetic moment in the excited state. Its very small magnitude indicates
nonaromatic character of a large 4N -electron system.
Fig. 1. Structure of cP6T6.
Keywords: porphyrins; MCD; electronic structure.
References
[1] O. Fenwick, J.K. Sprafke, J. Binas, D.V. Kondratuk, F. Di Stasio, H.L. Anderson, F. Cacialli, Nano
Lett. 11 (2011) 2451.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
271
T4: P–4
Steady state emission anisotropy measurement for investigate FRET
mechanism in Rhodamine 110 - peptide - Rhodamine 101 system in
PVA films
Michał Mońka
1
, Anna Synak
1
, A. Kubicki
1
, Urszula Łozowska
1
, and Beata Grobelna
2
1
Institute of Experimental Physics, Department of Mathematics, Physics and Informatics, University
of Gdańsk, Wita Stwosza 57, 80-308, Gdańsk, Poland, e-mail: michal.monka@ug.edu.pl
2
Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308, Gdańsk, Poland
Analysis of absorption, fluorescence emission and time-resolved emission spectra of
Rhodamine 110-peptide-Rhodamine 101 system in PVA films has shown energy transfer
process between donor (Rhodamine 110) and acceptor (Rhodamine 101). Beside the emission
spectra investigations, and time-resolved methods, the estimation of FRET mechanism
efficiency can be supported by steady state emission anisotropy (EA) measurement.
We present the experimental setup for EA spectra investigations in the modernized form (idea
and characteristic features are described) and results based on EA, time resolved and emission
spectra measurements for donor-acceptor (Rhodamine 101-peptide-Rhodamine 110) system. EA
values for the donor-peptide-acceptor system increase in the donor emission wavelength region
and decrease in the acceptor emission band which is associated with FRET occurrence.
Keywords: emission anisotropy; FRET; Rhodamine 101; Rhodamine 110
Acknowledgment
This research has been supported partially by the National Science Centre Poland grant
2015/17/B/ST5/03143 (A.S.,B.G.) and the University of Gdańsk (M.M, A.K.).
References
[1] A. Kubicki, Exp. Tech. Physik 37 (1989) 329.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
272
T4: P–5
Fine-line luminescence spectroscopy of metalloporphyrins
Michał Kijak
1
, Aleksander Gorski
1
, and Alexander Starukhin
2
1
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw,
Poland, e-mail: mkijak@ichf.edu.pl
2
B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Independence Av. 68,
220072, Minsk, Belarus
Metallocompexes of porphyrins are biologically relevant compounds known for many years.
However, despite intensive studies by many groups, their spectral features and photophysical
properties are still the subject of long debates and new experiments. The spectroscopic studies at low
temperatures belong to effective and proven methods of investigation of fine details such as a
vibrational structure of molecules in both the ground and excited states. One of the most spectacular
methods for recording fine-line luminescence spectra is the fluorescence line narrowing (FLN) [1].
The FLN method is based on selective laser excitation of chromophores embedded in a solid matrix at
liquid helium temperature. At low temperature, the homogeneous spectral broadening is strongly
diminished and upon optical selection of specific subpopulations from the inhomogeneously
broadened absorption band of the sample the fluorescence spectra transform from wide broad bands
into a set of narrow zero-phonon lines (ZPL). The difference in energy of a given ZPL and the
excitation laser is equal to the frequency of a vibrational mode of investigated compound [1].
In this report we will discuss a progress in studies of metalloporphyrins in different solid matrices
at cryogenic temperatures. Metallocomplexes of free-base porphyrin, octamethylporphyrin,
octaethylporphyrin, as well as compounds with asymmetric alkyl- substitution on β-positions with
Mg(II), Zn(II), Pd(II) and Pt(II) central ions have been investigated using FLN method. The planar
and two kinds of distorted conformers (“saddle” and “dome”) of Mg- and Zn-porphyrins were
detected by highly-resolved fluorescence [2] and fluorescence excitation spectra. Distorted forms of
Zn-porphyrin have been spectrally resolved in both the fluorescence and phosphorescence spectra.
One of the most exciting results is the observation of fluorescence excitation spectra with well-
resolved vibrational structure of the Soret band for Mg- and Zn-porphyrins in solid matrix of
tetrahydrofuran at 4.2 K (see Fig. 1). Vibrational modes with frequencies of 360, 719, 986, 1359 and
1477 cm
–1
were observed for electronic transitions
in that region for magnesium porphyrin.
Interestingly, the spectrum consists of two sets of
lines separated by 102 cm
–1
. The splitting can be
explained by the loss of degeneracy of two
electronic transitions present in the Soret band of an
isolated system caused by the interaction with solid
matrix and/or additional liganding by THF
molecule(s) leading to the deformation of the
macrocycle and loosing of its fourfold symmetry
Quantum-chemical modeling by means of DFT
methods was employed to quantify these effects.
The assignment of electronic transitions and
vibronic features observed in the spectrum will be
presented.
Keywords: metalloporphyrins; fluorescence line
narrowing; Soret band structure
Acknowledgment
This work was supported European Union’s Horizon 2020 research and innovation programme under grant
agreement No 645628 and Foundation for Fundamental Research of Republic of Belarus (project Ph16R-084).
References
[1] R.I. Personov, E.I. Al’Shits, L.A. Bykovskaya, Opt. Commun. 6 (1972) 169.
[2] A.S. Starukhin, A.M. Shul’ga, Opt. Spectrosc. 98 (2005) 780.
Fig. 1. Fluorescence excitation spectrum of the
“saddle” form of Mg-porphyrin in the Soret
band region.
Dostları ilə paylaş: |