Design and synthesis of porphyrin-based optoelectronic gates

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.