1058737-75-9Relevant academic research and scientific papers
Regiospecifically α-13C-labeled porphyrins for studies of ground-state hole transfer in multiporphyrin arrays
Muresan, Ana Z.,Thamyongkit, Patchanita,Diers, James R.,Holten, Dewey,Lindsey, Jonathan S.,Bocian, David F.
, p. 6947 - 6959 (2008)
(Figure Presented) Insight into the electronic communication between the individual constituents of multicomponent molecular architectures is essential for the rational design of molecular electronic and/or photonic devices. To clock the ground-state hole/electron-transfer process in oxidized multiporphyrin architectures, a p-diphenylethyne-linked zinc porphyrin dyad was prepared wherein one porphyrin bears two 13C atoms and the other porphyrin is unlabeled. The 13C atoms are located at the 1- and 9-positions (α-carbons symmetrically disposed to the position of linker attachment), which are sites of electron/spin density in the a1u HOMO of the porphyrin. The 13C labels were introduced by reaction of KS 13CN with allyl bromide to give the allyl isothiocyanate, which upon Trofimov pyrrole synthesis followed by methylation gave 2-(methyl-thio)pyrrole- 2-13C. Reaction of the latter with paraformaldehyde followed by hydrodesulfurization gave dipyrromethane-1,9-13C, which upon condensation with a dipyrromethane-1,9-dicarbinol bearing three pentafluorophenyl groups gave the tris(pentafluorophenyl)porphyrin bearing 13C labels at the 1,9-positions and an unsubstituted meso (5-) position. Zinc insertion, bromination at the 5-position, and Suzuki coupling with an unlabeled porphyrin bearing a suitably functionalized diphenylethyne linker gave the regiospecifically labeled zinc porphyrin dyad. Examination of the monocation of the isotopically labeled dyad via electron paramagnetic resonance (EPR) spectroscopy (and comparison with the monocations of benchmark monomers, where hole transfer cannot occur) showed that the hole transfer between porphyrin constituents of the dyad is slow (6 s -1) on the EPR time scale at room temperature. The slow rate stems from the a1u HOMO of the electron-deficient porphyrins, which has a node at the site of linker connection. In contrast, analogous dyads of electron-rich porphyrins (wherein the HOMO is a2u and has a lobe at the site of linker connection) studied previously exhibit rates of hole transfer that are fast (>5 × 107 s-1) on the EPR time scale at room temperature.
