Conformational and electronic effects of phenyl-ring fluorination on the photophysical properties of nonplanar dodecaarylporphyrins

Static and time-resolved optical measurements have been performed on a numb er of free-base and zinc dodecaarylporphyrins with varying degrees of fluor ination of the peripheral aryl rings. These studies were performed in a var iety of solvents of differing polarity and metal-ligating ability and at ro om and low temperatures. All of the compounds are deduced to be nonplanar b ased on their perturbed photophysical properties relative to planar analogu es and on the X-ray data available for these molecules. The dodecaarylporph yrins studied generally separate into two classes based on their photophysi cal properties and the presence or absence of meso-pentafluorophenyl rings. The photophysical properties are clearly affected by the electron-withdraw ing characteristics of these fluorinated phenyl rings, but structural effec ts derived from the interaction of the phenyl rings with each other, the ma crocycle, and the solvent are also apparent. Many of the differences in pro perties among the molecules studied and the perturbed photophysical propert ies of nonplanar porphyrins in general are associated with the ability of t hese molecules to undergo photoinduced conformational changes. For the dode caarylporphyrins, the perturbed properties are also a result of the ability of these compounds to access multiple conformations in the ground- and exc ited-electronic states. The studies demonstrate the strong linkage that non planar porphyrins have between their electronic properties, structural char acteristics, conformational dynamics, porphyrin-solvent interactions, and p hotophysical behavior. These connections are far stronger than those exhibi ted by planar porphyrins and lead to detailed differences in properties amo ng the compounds studied here as well as the photophysical properties of no nplanar porphyrins as a whole.