Optimization and Chemical Control of Porphyrin‐Based Molecular Wires and Switches

Abstract

The design rationale is described as are some experimental and theoretical developments concerning rigidly fused porphyrin molecular wires. These materials consist of porphyrin units fused to acene‐type bridges and have been synthesized in a range of topologies including linear porphyrin octamers of length ca. 120 Å. Next we demonstrate, for some linear oligoporphyrins, how the electronic coupling between the end porphyrin units can be modulated by simple (possibly in situ) chemical modulation of the bridging units. Specifically, the chemical systems considered involve either pH‐controlled protonation of bridge azines or conversion of bridge quinone or quinone dioxime rings to or from benzenoid or hydroquinone rings. In the most general terms, the electronic coupling through oligoporphyrin molecular wires is discussed in terms of a simple model in which complete end‐to‐end π electronic delocalization is required in order to provide strong long‐range interactions. Computationally, we monitor interorbital coupling using an appropriate mixture of density functional (B3LYP) and ab initio SCF computational schemes. Finally, we examine bridge modulation of the intermetallic coupling in three homovalent bis‐metallic oligoporphyrin systems, two in which Ru(CO)2 is complexed within terminal porphyrin rings, the other in which [Cu(I)Cl2]− is tethered using phenanthroline end groups. Results are obtained both using an effective two‐level model, appropriate for spectroscopic properties, and using a more general scheme, appropriate for molecular conduction.

The Appropriateness of Density‐Functional Theory for the Calculation of Molecular Electronics Properties

“…Porphyrins and chlorophylls are also molecules with extended π delocalization that have been proposed for many functions as molecular electronic devices 47–49. Their spectra contain a rich set of transitions that have never been unambiguously assigned,50,51 but most of the key features are well understood.…”

“…46 Porphyrins and chlorophylls are also molecules with extended π delocalization that have been proposed for many functions as molecular electronic devices. [47][48][49] Their spectra contain a rich set of transitions that have never been unambiguously assigned, 50,51 but most of the key features are well understood. DFT predicts 52,53 more states in the visible region that comes from simple analytical models or feasible ab initio calculations, 49,54,55 but the lack of a complete and unambiguous experimental assignment precludes the verification or otherwise of the DFT predictions.…”

Theoretical study of a neutral, doubly protonated, and doubly deprotonated porphyrin dithiolate used as a molecular switch

“…Furthermore, from a pragmatic point of view, the porphyrin stability and its relatively ease of utilization in synthetic chemistry made it one of the most important molecules in today's chemistry. However, the studies of porphyrinbased molecular junctions are relatively scarce [17,18], and conjugated and fused oligoporphyrins have also been used as molecular wires or switches [19][20][21][22][23][24][25]. The electrical properties of metalloporphyrins were also explored both experimentally [20] and theoretically.…”

Serendipitous synthesis of trimetallic porphyrazine triads

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Additionally, self-assemblies containing porphyrins with bipyridines, trans-PdCl 2 units, or ruthenium octahedra are of interest as molecular devices. [20][21][22][23] Binuclear metalloporphyrins and phthalocyanines linked by benzene ring fusion show intriguing redox and non-linear optical properties.…”