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Fluorescence and FTIR Spectra Analysis of Trans-A2B2-Substituted Di- and Tetra-Phenyl Porphyrins
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2010 (English)In: Materials, ISSN 1996-1944, no 8, 4446-4475 p.Article in journal (Refereed) Published
Abstract [en]

A series of asymmetrically substituted free-base di- and tetra-phenylporphyrins and the associated Zn-phenylporphyrins were synthesized and studied by X-ray diffraction, NMR, infrared, electronic absorption spectra, as well as fluorescence emission spectroscopy, along with theoretical simulations of the electronic and vibration structures. The synthesis selectively afforded trans-A2B2 porphyrins, without scrambling observed, where the AA and BB were taken as donor- and acceptor-substituted phenyl groups. The combined results point to similar properties to symmetrically substituted porphyrins reported in the literature. The differences in FTIR and fluorescence were analyzed by means of detailed density functional theory (DFT) calculations. The X-ray diffraction analysis for single crystals of zinc-containing porphyrins revealed small deviations from planarity for the porphyrin core in perfect agreement with the DFT optimized structures. All calculated vibrational modes (2162 modes for all six compounds studied) were found and fully characterized and assigned to the observed FTIR spectra. The most intense IR bands are discussed in connection with the generic similarity and differences of calculated normal modes. Absorption spectra of all compounds in the UV and visible regions show the typical ethio type feature of meso-tetraarylporphyrins with a very intense Soret band and weak Q bands of decreasing intensity. In diphenyl derivatives, the presence of only two phenyl rings causes a pronounced hypsochromic shift of all bands in the absorption spectra. Time-dependent DFT calculations revealed some peculiarities in the electronic excited states structure and connected them with vibronic bands in the absorption and fluorescence spectra from associated vibrational sublevels.

Place, publisher, year, edition, pages
2010. no 8, 4446-4475 p.
Keyword [en]
tetraphenyl porphyrin; asymmetric substitution; electronic structure; TD DFT; FTIR; fluorescence
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-28202DOI: 10.3390/ma3084446ISI: 000298242400015Scopus ID: 2-s2.0-84877263159OAI: oai:DiVA.org:kth-28202DiVA: diva2:385046
Funder
Swedish e‐Science Research Center
Note

QC 20110111

Available from: 2011-01-11 Created: 2011-01-11 Last updated: 2012-08-28Bibliographically approved
In thesis
1. Theoretical Studies of Raman Scattering
Open this publication in new window or tab >>Theoretical Studies of Raman Scattering
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Different theoretical approaches have been presented in this thesis to study the Raman scattering effect. The first one is response theory applied up to third order of polarization, where the determination of α, β and γ is used to calculate linear Raman scattering (resonance Raman scattering (RRS) and normal Raman scattering (NRS)), hyper Raman scattering (HRS) and coherent anti-Stokes Raman scattering (CARS), respectively. The response theory refers to adiabatic time-dependent density functional theory in the complex domain with applications on RRS and NRS, and to a recently developed methodology (Thorvaldsen et al. [105, 106]) for the analytic calculation of frequency-dependentpolarizability gradients of arbitrary order, here with applications on CARSand HRS. Various systems have been studied with the response theory, such as explosive substances (DNT, TNT, RDX and H2O2), optical power limiting materials (platinum(II) acetylide molecules), DNA bases (methylguanine-methylcytosine) and other systems (Trans-1,3,5-hexatriene and Pyridine). We have explored the dependency of the calculated spectra on parametrization in terms of exchange-correlation functionals and basis sets, and on geometrica loptimization.

The second approach refers to time-dependent wave packet methodology for RRS and its time-independent counterpart in the Kramers-Heisenberg equation for the scattering cross section, which reduces the calculation of the RRS amplitude to computation of matrix elements of transition dipole moments between vibrational wave functions. The time-dependent theory has been used to examine RRS as a dynamical process where particular attention is paid to the notion of fast scattering in which the choice of photon frequency controls the scattering time and the nuclear dynamics. It is shown that a detuning from resonance causes a depletion of the RRS spectrum from overtones and combination bands, a situation which is verified in experimental spectra.

The cross section of NRS has been predicted for the studied molecules to be in the order of 10−30 cm2/sr. A further increase in sensitivity with a signal enhancement up to 104 to 105 is predicted for the RRS technique, while CARS conditions imply an overall increase of the intensity by several orders of magnitude over NRS. In contrast to RRS and CARS, the HRS intensity is predicted to be considerably weaker than NRS, by about four orders of magnitude. However, silent modes in NRS can be detected by HRS which in turncan provide essential spectroscopic information and become complementary to NRS scattering.

With the above mention methodological development for NRS, RRS, CARS and HRS, we have at our disposal a powerful set of modelling tools for the four different Raman techniques. They have complementary merits and limitations which facilitate the use of these spectroscopes in applications of Raman scattering for practical applications, for instance stand-off detection of foreign substances.

Place, publisher, year, edition, pages
Stockholm: KTH, 2011. ii, 66 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2011:2
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-28332 (URN)978-91-7415-844-1 (ISBN)
Public defence
2011-01-28, FD51, AlbaNova, Universitetscentrum, Stockholm, 08:40 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note
QC 20110112Available from: 2011-01-13 Created: 2011-01-13 Last updated: 2012-05-24Bibliographically approved

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