Excitation energy migration in a dodecameric porphyrin box

The excitation energy hopping (EEH) in a dodecameric porphyrin box (TB2) prepared by self-assembly of four meso-meso linked zinc(ll) triporphyrin (T2)s is explored by picosecond fluorescence and femtosecond transient absorption (TA) spectroscopy. The exciton-exciton annihilation and anisotropy depolarization observed in both fluorescence and TA provide a consistent EEH rate, i.e. 300 20 ps(-1), assuming Forster energy hopping among four T2 units in TB2. The observed energy hopping time 300 20 ps(-1) is slower than the previous 98 3 ps(-1) of B2 (an octameric porphyrin box), even though the size of hopping unit is larger in TB2. (c) 2005 Elsevier B.V. All rights reserved.