Sequential FRET processes in calix[4]arene-linked orange-red-green perylene bisimide dye zigzag arrays

Perylene bisimide-calix[4]arene arrays composed of up to three different types of perylene bisimide chromophores (orange, red, and green PBIs) have been synthesized. Within these arrays, the individual chromophoric building blocks are positioned in defined spatial orientation and are easily replaceable by each other without influencing the overall geometric arrangement of the supramolecular system. The specific optical properties of the individual chromophore facilitated the investigation of photoinduced processes very accurately by time-resolved emission and femtosecond transient absorption spectroscopy. A quantitative analysis of the photophysical processes as well as their rate constants have been obtained by employing UV/vis absorption, steady state and time-resolved emission, femtosecond transient absorption spectroscopy, and spectrotemporal analysis of the femtosecond transient absorption data. These studies reveal very efficient energy transfer processes from the orange to the red PBI chromophoric unit (k(ET) = 6.4 x 10(11) s(-1) for array or), from the red to the green PBI (k(ET) = 4.0 x 10(11) s(-1) for array rg), and slightly less efficient from the orange to the green PBI (k(ET) = 1.5 x 10(11) s(-1) for array og) within these perylene bisimide-calix[4]arene arrays. The experimentally obtained rate constants for the energy transfer processes are in very good agreement with those calculated according to the Forster theory.