Crystallochemistry laboratory

Faculty of Chemistry, University of Warsaw

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Opus 10th

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Structure and photophysical properties of selected pirene derivatives in high pressure conditions

Grant OPUS, awarded to dr Anna Makal, financed by the Polish National Science Centre (NSC), at the Department of Chemistry, University of Warsaw, Poland.

The aim of the project is to investigate the relationships between the photophysical properties (UV-VIS spectra, lifetimes of the electronic excited states) and increased external pressure for selected 1- and 2- substituted pyrene derivatives, characterized by the presence of face-to-face π-stacking interactions in the solid state and displaying certain photophysical properties, such as enhanced fluorescence in the solid state and piezochromism.

Single crystal samples, obtained thanks to collaboration with the group of prof. Janusz Zakrzewski from the Department of Chemistry, University of Lodz, will be subjected to high pressures (in range from 0.1 to ~5GPa) using diamond high-pressure chambers (Diamond Anvil Cells, DAC).

Single crystal X-ray diffraction data collection and subsequent X-ray structure determination will be performed for each compound in ambient conditions as well as in DAC at a series of different high pressures. Raman spectra will be recorded at each pressure, in order to confirm the structural changes, followed by UV-VIS steady state and time-resolved spectroscopy, to determine the fluorescence spectra and the lifetimes of electronically excited states.

Systematic theoretical calculations using DFT methods will also be performed for each test compound, for the isolated molecules as well as in periodic conditions, including geometry optimization, determination of electronic energy levels (band structure) in the solid state, analysis of the electronic excitations (TD-DFT) and characterization of the strength of intermolecular interactions.

The particular goal is to determine the relationships between the crystal structure at high pressure and the resulting changes of photophysical properties and to describe the mechanism of the excimer formation in the investigated compounds. The results will allow a better understanding of the luminescence mechanisms of the investigated compounds. In particular, they will shed light on the reasons for the enhanced fluorescence efficiency of these compounds in the solid state. These findings may be crucial for the optimization of the known applications of the pyrene derivatives (in pressure sensors, light-emitting diodes a.s.o.) and proposing new, simpler and more efficient applications.

 


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