Abstract A series of 10-arylflavins (10-phenyl-, 10-(2′, 6′-dimethylphenyl)-, 10-(2′, 6′- diethylphenyl)-, 10-(2′, 6′-diisopropylphenyl)-, 10-(2′-tert-butylphenyl)-, and 10-(2′, 6′-dimethylphenyl)-3-methylisoalloxazine (2 a–f)) was prepared as potentially nonaggregating flavin photocatalysts. The investigation of their structures in the crystalline phase combined with 1 H-DOSY NMR spectroscopic experiments in CD 3 CN, CD 3 CN/D ...