Modeling processes of non-radiative relaxation of electronically excited states of fluorescent probe 4-dimethylaminochalcone and its complexes with water using non-adiabatic molecular dynamics

• Internal conversion to ground state is a path to lower quantum yield in polar media.
• The probe's hydration enhances non-radiative relaxation of the lowest excited singlet.
• The mobility of the polyene chain is a key factor in non-radiative relaxation process.

One of the most important parameters registered in fluorescent probes method is fluorescence quantum yield. For fluorescent probe DMAC (4-dimethylaminochalcone) it could vary by thousand times depending on its environment.Fluorescence quantum yield value is defined by rates of non-radiative processes – internal conversion and intersystem crossing. Those rates could be determined using non-adiabatic molecular dynamics.In the present work the rates of non-radiative decay from lowest excited singlet level to ground state were determined for DMAC molecule, and its complexes with one and two water molecules. Molecular dynamics modeling was performed in Newton-X package with addition of Turbomole, using TDDFT. Probability of non-adiabatic transition was obtained using Tully's fewest switches algorithm.Various factors that can influence the rates of non-adiabatic decay were evaluated, such as energy gap between the levels, values of coupling vectors. It was shown that the probability of non-radiative transition is mostly influenced by vibrational mobility of polyene chain in the middle of the molecule. That hypothesis agrees well with experimental data.

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