Realization of a “Lockable” Molecular Switch via pH- and Redox-Modulated Cyclization

A switchable organic system involving four distinct states that can be interconverted by use of both pH and redox chemistry as control parameters has been developed. The key molecules involved in this system are the phenanthridine-based heterocycles 1-isobutyl-1,2,3,12b-tetrahydroimidazo[1,2-f]phenanthridine (TIP) and 5-[2-(isobutylamino)ethyl]phenanthridinium (AEP). These two states are interchangeable via pH control, and in addition they can also be further manipulated by oxidation or reduction to convert them to their “pH-inert” forms: 1-isobutyl-2,3-dihydro-1H-imidazo[1,2-f]phenanthridinium (DIP) and 5-[2-(isobutylamino)ethyl]-5,6-dihydrophenanthridine (AEDP), respectively. UV and 1H NMR experiments carried out in a biphasic dichloromethane (DCM)/water solution were used for in situ structure determination. The results showed that the pH-modulated cyclization and phase-transfer process between the TIP and AEP states was essentially quantitative and repeatable without any significant loss in activity and that reduction or oxidation could be used to lock out these states against such acid−base-induced changes.