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A butterfly like motion as a clue to the photophysics of thioxanthone
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
2006 (English)In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 179, no 3, 298-304 p.Article in journal (Refereed) Published
Abstract [en]

A theoretical, quantum-chemical study of the thioxanthone (TX) molecule has been performed at the MP2 and CASPT2 levels of theory. Geometries, absorption energies, and transition and state properties have been investigated. Two conformers have been found very close in energy with planar (P) and non-planar (NP) structures, the latter characterized by a dihedral angle theta = 173.3 degrees representing the bend of the side benzene rings and an out-of-plane angle theta=4 degrees of the C=O bond. Large changes in the relative positions and properties of the two low-lying electronic absorption bands, pi pi* and n pi*, are computed when changing the conformation. As a consequence of the analysis of the TX absorption spectrum it is suggested that TX should be viewed as dynamically changing its conformation between the planar and the non-planar conformations. We coined such behavior as a "butterfly like motion". This dynamic view of the TX structure enables a plausible explanation of the photophysical properties observed for the system.

Place, publisher, year, edition, pages
2006. Vol. 179, no 3, 298-304 p.
Keyword [en]
thioxanthone, absorption spectrum, CASPT2, ground state structure
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5085DOI: 10.1016/j.jphotochem.2005.08.033ISI: 000236722300009Scopus ID: 2-s2.0-33644857241OAI: oai:DiVA.org:kth-5085DiVA: diva2:7840
Note
Tidigare titel: A butterfly effect as a clue to the unique photophysics of thioxanthone Uppdaterad från submitted till published: 20101011. QC 20101011Available from: 2005-04-28 Created: 2005-04-28 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Charge-transfer excitations and phtophysical properties of molecular building blocks
Open this publication in new window or tab >>Charge-transfer excitations and phtophysical properties of molecular building blocks
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis reports a state-of-the-art theoretical study of photophysical properties of organic charge-transfer aromatic molecules. These molecules are building blocks of molecular functional materials used in modern photonics technology and play essential roles in chemistry and biology in general. A good understanding of these systems is thus important.

The theoretical results for permanent dipole moments of some substituted benzenes have been obtained using the coupled cluster singles and doubles (CCSD) method. The performance of density functional theory (DFT) for the geometry and electronic properties has been compared with that of traditional ab initio methods, such as Hartree-Fock, second-order Möller Plesset perturbation theory (MP2), CCSD and CCSD(T). Limitations of the DFT methods for charge transfer molecules have been demonstrated. The multi-configuration self-consistent field (MCSCF) method has been applied to understand properties of the triplet states of benzene derivatives by studying their phosphorescence with the inclusion of contributions from vibronic coupling. It has also been employed to calculate the photophysics of the thioxanthone molecule containing three benzene rings in combination with the CASPT2 method, resolving a long-standing problem concerning the possible stable conformations of the molecule.

With knowledge of the building blocks a series of porphyrin derivatives with exceptionally large two-photon absorption cross sections were designed, and proposed for use in bioimaging applications. The static and dynamic properties of a few zinc and platinum organometallic compounds, being possible candidates for optical limiting devices, have also investigated.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 43 p.
Series
Theses in philosophy from the Royal Institute of Technology, ISSN 1654-627X
Keyword
Theoretical chemistry, Photophysical porperties, CCSD, CASSCF, Teoretisk kemi
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-184 (URN)91-7178-020-3 (ISBN)
Public defence
2005-05-12, FA32, Albanova centrum, 10:00
Opponent
Supervisors
Note
QC 20101011Available from: 2005-04-28 Created: 2005-04-28 Last updated: 2011-11-23Bibliographically approved

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