Picosecond Spectroscopic Studies of Tautomers of a Bisazo Compound in Solutions

Abstract

Abstract Spectroscopic properties of a fluorenone‐based bisazo compound in different organic solvents have been investigated by means of the steady‐state absorption and fluorescence spectroscopy and picosecond time‐resolved absorption pump‐probe spectroscopy. The spectra of the molecules have been shown to be mainly determined by the excitations localized on individual chromophores ‐ azo fragments. Spectra of the azo‐enol and hydrazone‐quinone tautomeric forms were distinguished. Excited states of the two forms were found to relax in different ways. The hydrazone‐quinone form relaxes predominantly nonradiatively with the 400 ps time constant in α‐chloronaphthalene, resulting in the fluorescence quantum yield of the order of 10 −2 . The azo‐enol form relaxes via two competing ways, directly to the ground state with the time constant of the order of tens of picoseconds, or via the long‐lived intermediate state.