The origin of radiationless conversion of the excited state in the kindling fluorescent protein (KFP): Femtosecond studies and quantum modeling

The Ala143Gly variant of the chromoprotein asCP from the sea anemony Anemonia sulcata, called the kindling fluorescent protein (KFP), is a promising candidate for the development of novel subdiffraction method of fluorescent microscopy. The pump-probe method with the delay times between the pump and probe pulses up to 5 ps was applied to study dynamics of the primary processes upon excitation of KFP. The differential absorption spectra at 80 fs delay showed the absorption peak in the range 450–510 nm with the maximum wavelength at 490 nm, which diminished almost twice by intensity by 400 fs and practically disappeared by 1.5 ps. The quantum calculations showed that upon photo-excitation of KFP to the first excited state S1, the fast radiationless relaxation occurred to the ground state S0 due to rotation of the phenolic fragment of the chromophore.