Deep-Red Emissive BODIPY-Chlorin Arrays Excitable with Green and Red Wavelengths

We report here the synthesis and characterization of BODIPY-chlorin arrays containing a chlorin subunit, with tunable deep-red (641-685 nm) emission, and one or two BODIPY moieties, absorbing at 504 nm. Two types of arrays were examined: one where BODIPY moieties are attached through a phenylacetylene linker at the 13- or 3,13-positions of chlorin, and a second type where BODIPY is attached at the 10-position of chlorin through an amide linker. Each of the examined arrays exhibits an efficient (>= 0.80) energy transfer from BODIPY to the chlorin moiety in both toluene and DMF and exhibits intense fluorescence of chlorin upon excitation of BODIPY at similar to 500 nm. Therefore, the effective Stokes shift in such arrays is in the range of 140-180 nm. Dyads with BODIPY attached at the 10-position of chlorin exhibit a bright fluorescence in a range of solvents with different polarities (i.e., toluene, MeOH, DMF, and DMSO). In contrast to this, some of the arrays in which BODIPY is attached at the 3- or at both 3,13-positons of chlorin exhibit significant reduction of fluorescence in polar solvents. Overall, dyads where BODIPY is attached at the 10-position of chlorin exhibit similar to 5-fold brighter fluorescence than corresponding chlorin monomers, upon excitation at 500 nm.