... 25], the proton transferred from the phenol in the excited state is accepted by a heterocyclic nitrogen much ... between the phenol and the pyridine nitrogen to which, as evidenced by its strongly deshielded chemical shift (14.2 ... Hs 1, 3, 4, 5), 8.38 (d, J = 7 Hz, H-3',5'), 8.72 (t, J = 6 Hz ...