Synthesis and Fluorescence of a Series of Multichromophoric Acenaphthenyl Compounds

A novel free radical trapping reaction based on a stepwise radical reversible addition−fragmentation mechanism has been utilized to synthesize a series of acenaphthenyl dimers and trimers. The synthetic procedure involves the reaction of acenaphthylene with dithiobenzoate compounds (SC(Ph)SR) in the presence of a free radical initiator followed by reduction of the dithiobenzoyl end group with tributyltin hydride. Stereoisomers of the compounds have been isolated and their structures determined by proton NMR and X-ray crystallography. The solution fluorescence of the compounds has been characterized to reveal the requirements for intramolecular excimer (excited-state dimer) formation. Only in compounds containing identical stereochemical arrangements of adjacent acenaphthenyl groups is excimer fluorescence observed following photoexcitation.