Synthesis, ensemble, and single molecule characterization of a diphenyl-acetylene linked perylenediimide trimer

Perylenediimide (PDI) dyes have attracted a great deal of attention as they possess excellent photochemical stability, high extinction coefficients, and fluorescence quantum yields. The use of multiple PDI chromophores in one synthetic architecture increases their versatile use and functionality even more. However, bringing multiple chromophores in close proximity also leads to interactions among the chromophores and opens up new photophysical pathways. Here, the synthesis and photophysical characterization, both at the ensemble and single molecule level, of a diphenyl-acetylene linked perylenediimide trimer (3PDIAc) is presented. Forster type energy transfer processes like energy hopping and singlet-singlet annihilation among the chromophores are investigated. Despite the lower singlet-singlet annihilation rate of the phenoxy substituted perylenediimide chromophores (356 ps) versus for example perylenemonoimide (10 ps), the system still behaves as a single photon emitter. Sequential fitting of the dipole emission pattern recorded with defocused wide field imaging of single 3PDIAc, immobilized in a PMMA polymer film, demonstrated that emission can switch between sequential emission of all of the chromophores or emission from one chromophore that likely is the lowest in energy.