Redox-controlled fluorescence modulation in a BODIPY-quinone dyad

The synthesis and properties of two closely related boron dipyrromethene (BODIPY) derived dyads, incorporating redoxactive quinone units appended at the meso position, are described. For one dyad, the quinone unit is attached directly to the BODIPY core, whereas a phenylene spacer separates the two units in the second compound. Each of the quinone units is readily converted, by both chemical and electrochemical means, to the corresponding hydroquinone derivative. The strong fluorescence normally associated with the BODIPY unit is efficiently quenched in both dyads in their quinone forms. This is attributed to deactivation of the first excited singlet state by a way of an intramolecular electron-transfer process. By comparison, moderately intense fluorescence is observed for the hydroquinone derivative containing the phenylene spacer, but not for the analogous directly coupled dyad. The potential sensing capabilities of the phenylene-spaced BODIPY quinone and hydroquinone dyads, towards reducing and oxidising species such as ascorbate and peroxide, were tested in a biomembrane mimic. A reversible modulation in fluorescence could be readily detected by eye under standard UV-Iight excitation. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).