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.

Two porphyrin-based optoelectronic gates and several prototypical redox-switching components of gates have been synthesized for studies in molecular photonics. Linear and T-shaped molecular optoelectronic gates contain a boron-dipyrrin (BDPY) dye as the input unit, a zinc (Zn) porphyrin as the transmission unit, a free base (Fb) porphyrin as the output unit, and a magnesium (Mg) porphyrin as the redox-switching unit. The linear gate and T gate were synthesized using a molecular building block approach. In the linear gate synthesis, a BDPY−Zn porphyrin dyad was coupled with a Fb porphyrin−Mg porphyrin dimer. The synthesis of the T gate utilized a Zn porphyrin bearing four different meso substituents:  mesityl, 4-iodophenyl, 4-[2-(trimethylsilyl)ethynyl]phenyl, and 4-[2-triisopropyl)ethynyl]phenyl. Attachment of the three different groups to the Zn porphyrin was accomplished using successive Pd-mediated coupling reactions in the following sequence:  Fb porphyrin (output unit), BDPY dye (input unit), and Mg porphyrin (redox-switching unit). Both the linear gate and T gate syntheses introduce the Mg porphyrin at the final step to minimize demetalation of the Mg porphyrin. Refinements to various components of these gates were investigated through the preparation of a ferrocene−porphyrin, a ferrocene−phthalocyanine, and a ferrocene−porphyrin−phthalocyanine. A dyad motif for studies of optically based redox switching was prepared that contains a derivative of Ru(bpy)3X2 coupled to a porphyrin. From these and related studies have emerged a number of design considerations for the development of refined optoelectronic gates.

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