π...π-interactions of flavins,-II. [3.3](3,10)Isoalloxazinophane and quinhydrone-like flavin interactions

To study flavin-flavin interactions 3.3](3,10)isoalloxazinophane was synthesized and its structure determined as $\text{4}$. Electron spectra including charge-transfer absorptions of semi-reduced states are reported for $\text{4}$ in comparison with the mono-bridged bis-flavin analogue $\text{3}$.