XIV
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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
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T7: O–2
Combined Picosecond Time-Resolved and NMR techniques
used as a useful tool for investigation of excited state processes.
The case of excited state intramolecular charge separation and T-T energy transfer.
J. Dobkowski, M. Pietrzak, M. Kijak, M. Vengris, J. Waluk
1
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw,
Poland, e-mail: jdobkowski@ichf.edu.pl
2
Vilnius University, Sauletekio 10, LT10223 Vilnius, Lithuania
Excited state reaction, such as proton/electron transfer can generate significant changes in
the molecular geometry. The excited states characterized by significant or full transfer of
electron from a donor to an acceptor group can be categorized applying the minimum/maximum
overlap rule. This rule postulates that the overlap between the donor and acceptor molecular
orbitals involved in the electron transfer should reach the maximum or minimum value [1]. The
subject of this presentation deals with significant geometry transformation of the molecular
skeleton, which leads to the donor and acceptor decoupling (Twisted Intramolecular Charge
Transfer, TICT state [2]).
For monitoring temporal sequences of the elementary events femto/pico time-resolved
techniques are commonly used. However, these techniques cannot determine the geometry
transformation which occurs on the excited state energy degradation path. The NMR
spectroscopy is commonly used to determine the ground state geometry of molecules. The UV-
induced time-resolved NMR techniques enable observing the transient perturbation of the
ground state population produced by the excited state relaxation processes. This provides a
possibility to deduce the excited state geometry transformation [3].
The registration of the NMR spectra of an excited triplet state may seem to be a hopeless
case; nevertheless, we gave it a try. Two factors are critical for a successful realization of such
experiment: lifetimes of the triplet state and the efficiency of the intersystem crossing transition.
The
3
nπ* triplet states are short-lived, and therefore only molecules that have the lowest state
of
3
ππ* type can be considered as the objects giving the chance for a successful realization of the
NMR experiment. Let us concentrate our attention on the naphthalene molecule. The triplet state
of naphthalene can be produced without intermediacy of its singlet by triplet-triplet energy
transfer, either inter- or intramolecular. In the case of intermolecular energy transfer the
concentration of the donor and acceptor should be high, even 10
-1
M, which limits the
penetration length of the exciting pulses inside the volume of the sample and generates serious
experimental difficulties. That is the reason why the intramolecular mechanism of the generation
of the naphthalene triplet state was selected. The objects of our studies were spiro[9,10-dihydro-
9-oxoanthracene-10,2’-5’,6’-benzindan] and spiro[9,10-dihydro-9-oxoanthracene-10,2’(3’H)
phenalene] [4]. The results show that for T-T energy transfer mutual arrangement of the planes
of the donor and acceptor groups plays the crucial role.
Keywords: NMR; TICT state
References
[1] Z.R. Grabowski, J. Dobkowski, Pure Appl. Chem. 55 (1983) 245.
[2] Z.R. Grabowski, K.Rotkiewicz, W. Rettig, Chem. Rev. 103 (2003) 3899.
[3] J. Dobkowski, J. Wójcik, W. Koźmiński, R. Kołos, J. Waluk and J. Michl, J. Am. Chem. Soc. 124
(2002) 2406.
[4] R.A. Keller J. Am. Chem. Soc. 90 (1968) 1940.
XIV
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International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
111
T7: O–3
Spectroscopic investigation of molecular self-assembly
on bioactive glass particles
Simion Simon
1
1
Faculty of Physics & Interdisciplinary Research Institute on Bio-Nano-Sciences, Babes-Bolyai
University, 400084 Cluj-Napoca, Romania, e-mail: simons@phys.ubbcluj.ro
Bioactive glasses attracted great attention for medical applications mainly in bone tissue
repair [1], but also for soft tissue repair [2]. These applications are connected with their surface
properties when exposed to biological or simulated biological environments.
Structural changes occurred at the interface of bioactive glass particles with simulated body
fluids (SBF) were investigated by several techniques including infrared spectroscopy and magic
angle spinning nuclear magnetic resonance (MAS-NMR). The
29
Si and
31
P MAS-NMR results
show that silicate species with two and three bridging-oxygens per SiO
4
tetrahedra and PO
4
monomeric units dominate the structure of the investigated samples. The peak deconvolution
and data analysis of the NMR data were performed with DMFit program [3].
After immersion in SBF new Q
4
silicate species with four bridging oxygens appear as result
of silica-gel layer formed on microspheres surface (Fig. 1).
Fig. 1.
29
Si MAS-NMR spectra of bioactive glass particles before (a) and after immersion (b) in SBF.
The self-assembly of crystalline hydroxyapatite type layer is reflected by the occurrence of
narrow components in 31P MAS-NMR spectra.
Keywords: bioactive glass particles; molecular self-assembly; MAS-NMR.
Acknowledgment
Financial support from UEFISCDI-Romania, in framework of PN-II PCCA 78/2012 project, is gratefully
acknowledged.
References
[1] L.L. Hench, J. Mater. Sci. Mater. Med. (2006) 967.
[2] V. Miguez-Pacheco, L.L. Hench, A.R. Boccaccini, Acta Biomater. (2015) 1.
[3] D. Massiot, F. Fayon, M. Capron, I. King, S. LeCalve, B. Alonso, J.-O. Durand, B. Bujoli, Z. Gan, G.
Hoatson, Magn. Reson. Chem. (2002) 70.
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