16. mail kell 15.00 kaitseb Wojciech Kuznik materjaliteaduse erialal doktoritööd teemal "Quantum-chemical computer simulations of the linear and non-linear optical properties of pyrazoloquinoline and dicyanopyrazine derivatives" ("Pyrazoloquinoline ja dicyanopyrazine derivaatide lineaarsete ja mittelineaarsete optiliste omaduste kvantkeemilised arvutisimulatsioonid").
Juhendaja: Prof. Mikhail G. Brik (materjalide kompuutermodelleerimise professor, TÜ Füüsika Instituut)
1) Professor Bohdan Andriyevskyy, Department of Electronics and Computer Sciences, Koszalin University of Technology, Poland
2) Dotsent Mihhail Klopov, TTÜ Matemaatika-loodusteaduskond
The quantum-chemical computer simulations have been successfully used to aid material design of the studied groups of optically active substances. Pyrazoloquinoline derivatives containing fluorine atom, a promising branch of luminescent molecules with potential application in LEDs and other electroluminescent devices, have been subjected to Molecular Mechanics, semi-empirical and DFT analysis (Publication I). Molecular geometry, energy levels and electronic transition energies have been described by theoretical simulations and the results are consistent with the corresponding experimental data. Semi-empirical Configuration Interaction simulation accurately reproduced excited states and optical transitions. In the studied pyrazoloquinoline derivatives the PM3 model underestimated the energy gap by 41 (first absorption maximum at 437 nm against experimental 396 nm), while the AM1 and RM1 simulations were more accurate. No significant improvement in RM1 results were observed in comparison with its predecessor, AM1. In practical applications chromophores are almost never used in pure form. Typically they are placed in a transparent matrix, like a solvent or polymeric material. The matrix influences the chromophore and its optical properties and it is important to take that into account during new material design. Density Functional Theory models implemented in quantum-chemical packages can use solvation models to account for environmental influence on the studied molecules. In this work Polarizable Continuum Model was proven to be a very effective method to incorporate solvation effects in theoretical description of pyrazoloquinoline derivatives containing fluorine atom (Publication II). The choice of common solvents of different polarity as model matrices enabled facile experimental confirmation of the calculated solvatochromic effect. The environment's influence on optical properties of pyrazoloquinoline fluoroderivatives was rather small, but well within the detection range (5 nm difference in the first absorption peak maximum) and it was correctly reproduced by TDDFT/PCM simulations. It is reasonable to predict that PCM will also be effective in the case of polymeric matrices and in prediction of higher order hyperpolarizabilities in future research. Computer simulations have been successfully applied to theoretically describe the NLO response in a series of dicyanopyrazine derivatives belonging to the push-pull chromophore group. Molecular structure is known to significantly influence the nonlinear optical properties of the material. As it was demonstrated in Publication III, the π-linker connecting the electron-donating and electron-accepting groups can play crucial role in the intramolecular charge transfer process, especially if it ensures planarity of the equilibrium molecular geometry. The theoretically derived second order dynamic hyperpolarizabilities correlated very well with experimental data from the Second Harmonic Generation measurement. Energy gaps calculated from the HOMO and LUMO difference also correlated very well with the empirical data obtained from a cyclic voltammetry oxidation and reduction peaks. Computational chemistry methods have proven to be a useful tool in all the cases presented in this work. As such, they can be used to aid design of new optically active materials in future research in the field of both linear and non-linear optics. Additionally, incorporation of solvation models into DFT and TDDFT calculations can be used to predict matrix influence on optical properties of the embedded chromophores which can prove very useful in practical applications.