Electronic Communication across Porphyrin Hexabenzocoronene Isomers

Abstract

Single-molecule electronic components (SMECs) are envisioned as next-generation building blocks in quantum circuit systems.However,challenges such as the reproducibility of the electrode attachment to the individual molecules hamper their fundamental investigation. Foro ur purpose,w ei ntroduced quasi optoelectronic electrodes (QOEs) that allowf or rapid investigations of the properties and suitability of compounds for molecular electronic devices.I np articular,w e probed hexa-peri-hexabenzocoronene (HBC) as am odel system for D 6h -symmetrical nanographenes,w ith porphyrins as QOEs attached to the periphery.Weprepared selectively bisporphyrin-functionalized HBCs with ortho-, meta-and parasubstitution and studied their communication properties,i n correlation to the geometrical alignment and size of the system, by electrochemistry and optical spectroscopy. Further insights into structure-property relationships were gained by DFT calculations and X-raydiffraction analysis.

Multiple‐Porphyrin Functionalized Hexabenzocoronenes

“…Compared with the HPB analogues, the porphyrins’ B‐band is split and considerably broadened, if more than one porphyrin is attached to the HBC core. Similar characteristics were observed for recently reported bis‐porphyrin‐substituted HBCs, which showed, depending on the substitution geometry, split B‐band absorptions as well (Figure S11, Supporting Information). Interestingly, the right (lower‐energy) maximum is always located at the same position, 432 nm, for 7 , 8 , 11 , as well as for para ‐bis‐porphyrin‐HBC and only the left (higher‐energy) maximum is shifted.…”

“…On the one hand, the large aromatic π‐system of the HBC itself influences the porphyrins’ electronic characteristics (compare mono‐porphyrin HPB 3 vs. HBC 6 ) and on the other hand, the HBC unit facilitates electronic interaction between the porphyrins. In our study with bis‐porphyrin substituted HBCs we already investigated the communication ability across HBC bridges and suggested that the degree of the B‐bands’ distortion can be used as a qualitative tool to measure the electronic interaction between the porphyrins . The herein presented porphyrin‐HBCs follow this trend, for example, tri‐porphyrin substituted HBC 8 has a broader (FWHM 30.7 nm) and more split (12 nm) B‐band absorption as the isomer 7 .…”

“…First, mono‐porphyrin‐HBC 6 , previously made by us through a different route, was prepared as a reference compound (Scheme ). For this purpose, mono‐porphyrin‐tolane 1 was synthesized in a literature‐known statistical porphyrin condensation and reacted with tetracyclone 2 to the mono‐porphyrin‐HPB 3 . The transformation to the respective HBC derivative 6 worked almost quantitatively using FeCl 3 as the oxidant.…”

“…However, systems in which one HBC is connected to several porphyrins have remained unknown until very recently. This year, our group reported the synthesis of a series of bis‐porphyrin‐HBC conjugates (Figure ), which was utilized to study the effects of the HBCs’ substitution geometry . Furthermore, bis‐porphyrin‐substituted HBCs and extended HBC derivatives, were very recently prepared to investigate the influence of the nanographenes’ length .…”

“…Herein, we describe the synthesis of multiple‐porphyrin HBC conjugates with a functionalization degree of up to six porphyrins per HBC and study the effect of the number of porphyrins on the characteristics (Figure ). For that purpose, HBCs substituted by several porphyrins were prepared by either Scholl transformations of respective porphyrin‐HPBs, or by Suzuki type cross‐coupling reactions between iodo‐HBCs and boronic ester porphyrins …”