title: Effects of Metalation State (Free Base, Mg, Zn, Cd) on Excited-State Energy Transfer in Diarylethyne-Linked Porphyrin Dimers.
abstract: The ground- and excited-state properties of two new porphyrin dimers have been examined using static and time-resolved optical techniques. One dimer consists of a zinc porphyrin and a magnesium porphyrin (ZnMgU), and the other dimer consists of a cadmium porphyrin and a free base (Fb) porphyrin (CdFbU). In both arrays, the porphyrins are joined by a diarylethyne linker at one meso position with mesityl groups at the nonlinking meso positions. The rates of photoinduced energy transfer are faster for ZnMgU ((9 ps)(-)(1)) and CdFbU ((15 ps)(-)(1)) than found previously for ZnFbU ((24 ps)(-)(1)) and MgFbU ((31 ps)(-)(1)). Only for CdFbU does the yield of excited-state energy transfer (87%) drop below the near-quantitative (>/=99%) level, and this effect derives solely from competition with a very short inherent lifetime ( approximately 100 ps) of the photoexcited Cd porphyrin. The results further illustrate (1) the efficacy of this dimeric architecture for ultrafast excited-state energy transfer, (2) how molecular/electronic properties can be manipulated to tune photoinduced energy flow in multiporphyrin arrays, and (3) key factors impacting effective inter-porphyrin electronic communication, including porphyrin orbital tuning.
authors.affiliation: Departments of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, Washington University, St. Louis, Missouri 63130-4899, and University of California, Riverside, California 92521-0403.
authors.forename: Philippe
authors.initials: P
authors.lastname: Hascoat
authors.forename: Sung Ik
authors.initials: SI
authors.lastname: Yang
authors.forename: Robin K.
authors.initials: RK
authors.lastname: Lammi
authors.forename: Jennifer
authors.initials: J
authors.lastname: Alley
authors.forename: David F.
authors.initials: DF
authors.lastname: Bocian
authors.forename: Jonathan S.
authors.initials: JS
authors.lastname: Lindsey
authors.forename: Dewey
authors.initials: D
authors.lastname: Holten