STEROID-BRIDGED ANTHRYLOLIGOTHIENYLPORPHYRINS - SYNTHESIS AND STUDY ON THE INTRAMOLECULAR ENERGY-TRANSFER

The novel steroid-bridged energy transfer system 2 was prepared starti ng from epi-androsterone, The linkage of both the anthrylthienyl and t he bithienyl group in the 3- and 17-position of the steroid was achiev ed by Grignard reaction of the respective carbonyl function of the ste roid component. The synthesis was accomplished by linkage of the porph yrin group according to Lindsey's method. This synthetic strategy also enables the approach to molecular subunits required as reference comp ounds. The photophysical properties were studied using time-resolved f luorescence and fluorescence excitation spectroscopy. Reference donor molecule 6 exhibits-in analogy to other anthryloligothiophenes studied -a dual fluorescence: a blue anthracene-like fluorescence and a dynami cally coupled delayed red fluorescence resulting from the relaxed exci ted state. On the basis of these results, supermolecule 2 was investig ated. Besides the typical porphyrin emission, a high energetic fluores cence (blue fluorescence) was detected in 2 which results unambiguousl y, as stated from spectra of 6, from the donor part of 2. The lifetime of this fluorescence is shortened compared with that of 6. Supermolec ule 2 is the first in the series of our energy transfer systems exhibi ting donor fluorescence despite a very efficient intramolecular energy transfer (at least 99%).