Molecular recognition of guest molecules in organic host crystals probed by fluorescence spectra

The fluorescence spectra of 9,10-bis(3,5-dihydroxyphenyl)anthracene (ABR) in various alcoholic solvents show no solvent effect. However, recrystallized crystals have characteristic spectra depending on solvents used. The fluorescence peak is shifted from 464(methanol) to 426 nm (1-butanol) with an increase in alkyl chain length. When the crystals are evacuated in vacuum, the fluorescence peak changes to 450 nm.The peak corresponds to that of the crystal as received. It is known that ABR crystals form cavities composed of hydrogen-bonded polyresorcinol chains and anthracene columns, which incorporate two guest molecules. From the fluorescence spectral changes of ABR crystals with various guest molecules, it is indicated that the cavities can incorporate and recognize the guest molecules. Wet crystals obtained from ethanol/water suspension show complicated spectral changes during the drying, suggesting the effect of coincluded guest water molecules.