Photophysics of fisetin has been studied in solid lipid nanoparticle (SLN).
pH of the solutions was varied from 5 to 9.
The neutral and anionic forms of fisetin coexist in ground state.
In the excited state and at low pH, the anionic form of fisetin predominates.
Limited percolation of H+ and OH− ions occurs in the SLNs.