Linear and multilinear relationships between some solvent polarity parameters and solvatochromic
shifts of absorption and fluorescence of 2,2′-dihydroxy-1,1′-binaphthalene (DHBN) revealed strong
charge transfer excitations (formation of S1,CT with higher dipole moment) in this dipolar system. This dihydroxy
molecule with pKa(S0) of 10.9 becomes a weak acid with pKa(S1) of 6.8 in its first excited singlet state.
We studied the excited state proton-transfer process from DHBN to the base water in acetonitrile solution
by means of fluorescence spectroscopy. We found that the process occurs via a 1: 1 very weak (with equilibrium
constant K=9×10−3M−1) hydrogen-bonded adduct between the photoacid DHBN and the base.
Moreover, the rate constant of fluorescence quenching of DHBN by some Lewis acids; Ag+1, Cu+2, Fe+2 or Fe+3 metal ions in methanol solution as well as the binding constant of the formed complexes are correlated
with the size and charge of the metal ion. Furthermore, photostability studies of DHBN in aqueous solutions
at different pHs point to photolability of DHBN with formation of different photo-oxidation products similar
to simple naphthols.
