Study of the effect of β-cyclodextrin on the photophysics of alloxazines in the solid state

The influence of β-cyclodextrin (β-CD) on the photophysics of alloxazines† (lumichrome, Lch; 7-methylalloxazine, 7MA11; and 8-methylalloxazine, 8MA11) has been studied in the solid state by ground-state absorption and steady-state fluorescence methods. We support the existence of inclusion complexes between Lch and β-CD in water. The presence of similar complexes for 7MA11 and 8MA11 has also been found. Complexes of alloxazines and β-CD are also present in the solid state. The formation of hydrogen bonds in solid inclusion complexes between alloxazines and β-CD have been postulated in order to explain the luminescence behaviour of these solid complexes. New spectroscopic evidence has been found in the solid state of doubly hydrogen-bonded lumichrome dimers capable of executing double proton transfer in the excited state.