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Monday, July 14, 2008

The electronic structure of selected betaine dyes. A quantum chemical study

This thesis presents electronic absorption spectra, non linear optical properties and geometrical parameters of betaine dyes obtained by quantum chemical calculations.

Four betaines [4-(1-piridinium-phenolan), 3-(1-piridinium-phenolan), 2-(1-piridinium-phenolan) and 4-(1-piridinium-thiophenolan)] were selected for the study.

During the research various ab initio methods were applied. The Hartee-Fock method (HF) and the second order Møller-Plesset perturbation theory (MP2) were used to determine a geometrical and NLO properties. Moreover, the NLO were obtained using chosen variants of the coupled cluster metod (CC2, CCSD) and the geometry optimizations were perform using the Density Functional Theory (DFT/B3LYP) as well as complete active space methods (CASSCF and CASPT2). In the case of spectroscopic properties the CC and CASSCF/CASPT2 methods along with Time-Dependant DFT (with B3LYP, PBE0 and CAM-B3LYP functionals) and the Configuration Interaction with Singles (CIS and CIS(D)) were used.

Results obtained during the study indicate that the correct description of betaine dyes' electronic structure is an unusually demanding test for present quantum chemical methods. It is safe to say, that, for all of the investigated parameters, the electron correlation has to be take into account. It is also worth to notify that basis set selection is less important. However, diffuse and polarisation functions should be included in the case of spectroscopic and optical properties.

The presented computational result confirmed the very strong interaction between a betaine molecule and its environment. One of the outcome of this phenomena is a large difference between experimental results (usually obtained in condense phases) and theoretical data (calculated in vacuum). Another observation verified during project is the significant increase of the betaines' NLO by the conformational shifting. Finally, it is worth notify that the largest NLO response was obtained for 4-(1-piridinium-thiophenolan).

How you can quest I'm a doctor now! I defended my thesis (abstract above) 19th of June 2008 and my degree was confirmed by faculty of Chemistry board 26th of June. Thesis was written in Polish, so it isn't very useful for most of the world. However, there is the appendix with all available theoretical data of geometrical and spectroscopic parameters of betaine dyes. Additionally, some of results was published in following articles: JMM-11, JMM-13 and LETT-411 (I hope to write one, maybe more). PDF with thesis can be download here.

If I find some time I will might prepare English version of mentioned appendix, and of course, I will share my LaTeX, gnuplot, computational experience.

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