One‐Dimensional Porphyrin–Fullerene (C₆₀) Assemblies: Role of Central Metal Ion in Enhancing Ambipolar Mobility

Abstract

One-dimensional (1D) nanostructures of π-conjugated molecules exhibiting excellent charge carrier mobilities have attracted much interest for use in organic electronic devices. Although it is tedious to form such structures, the availability of highly delocalized electron and hole carriers in these donor (D)-acceptor (A) coassemblies realize ambipolar charge transport. Here we demonstrate the use of a simple solution casting method to create an ambipolar donor-acceptor single-crystalline assembly. 1D assemblies of 5,10,15,20-tetraphenylporphyrins (H TPP, ZnTPP) and fullerene (C ) exhibit high ambipolar mobility in the range of 0.8-3.4 cm Vs for electrons and holes with high ON/OFF ratio and low threshold voltage. A direct experimental proof for the pivotal role of the central Zn in tetraphenyl porphyrin, which enables a strong D-A charge transfer interaction in the cocrystal and thereby induces electron (1.35 cm Vs ), hole (3.42 cm Vs ) mobilities, the highest reported for two component D-A assemblies using solution casting, is demonstrated.

Multifunctional Features of Organic Charge‐Transfer Complexes: Advances and Perspectives

“…This co‐crystal behaved as a semi‐metallic material at room temperature with a σ value of 1.08×10 3 Ω −1 m −1 and a high hole mobility of 4.21 cm 2 V −1 s −1 in vacuum (Figure 14 a), which is attributed to significant π–π interactions and the Co–C short contact interactions observed in the optimized geometry (Figure 14 b). For another example, 1D transfer co‐crystals of 5,10,15,20‐tetraphenylporphyrins (H 2 TPP, ZnTPP) and fullerene (C 60 ), prepared through a simple solution processing technique, demonstrate excellent ambipolar transport performance in argon environment, and the average electron and hole mobility of H 2 TPP‐C 60 devices are 1.12 cm 2 V −1 s −1 and 0.86 cm 2 V −1 s −1 , 1.35 cm 2 V −1 s −1 and 3.42 cm 2 V −1 s −1 for ZnTPP‐C 60 co‐crystal devices, respectively [84] . The presence of the porphyrin center metal ion was believed to play a crucial role in the strong D‐A interaction with C 60 and greatly reduce the π–π stacking distance between porphyrin and C 60 .…”

Supramolecular Engineering of Crystalline Fullerene Micro‐/Nano‐Architectures

“…[123] To further investigate the effect of the metal ion of porphyrin on the assembly and the final functions of FMNAs, numerous studies have been performed by directly comparing two 5,10,15,20-tetraphenylporphyrins (H 2 TPP and ZnTPP) for co-crystallization with C 60 or C 70 ; the results reveal that uniform rods and nanosheets were obtained with C 60 and C 70 for both TPPs, respectively. [104,106] Moreover, the central Zn ion in ZnTPP is critical for improving the hole and electron mobilities to record values of 2.11 and 0.98 cm 2 V −1 s −1 , which are the highest among all the reported ambipolar organic donor-acceptor (D-A) co-assemblies. [104] Moreover, the strong mutual interactions between fullerene and porphyrin were further corroborated in C 70 /ZnTPP co-crystals, in which a radical-ion pair state with a full charge transfer was confirmed using photo-physical measurements.…”

“…[104,106] Moreover, the central Zn ion in ZnTPP is critical for improving the hole and electron mobilities to record values of 2.11 and 0.98 cm 2 V −1 s −1 , which are the highest among all the reported ambipolar organic donor-acceptor (D-A) co-assemblies. [104] Moreover, the strong mutual interactions between fullerene and porphyrin were further corroborated in C 70 /ZnTPP co-crystals, in which a radical-ion pair state with a full charge transfer was confirmed using photo-physical measurements. [122] In addition to porphyrins, an extended viologen-based cyclophane (ExBox 2 4+ ) has also been used for the co-crystallization with C 60 to generate red 1D needle-shaped FMNAs.…”

“…[105,123] Alternatively, changing the porphyrin component from H 2 TPP to ZnTPP in the co-crystals dramatically improves the hole and electron mobility to record values of 2.11 and 0.98 cm 2 V −1 s −1 , respectively. [104] In addition to the major D-A dyads in the co-crystals, other complementary components such as solvent molecules and surfactants also play an important role in the charge transfer process. For example, the activation/deactivation of charge-transfer interactions between Y@C 82 /NiP is dominated by solvents used for the co-crystallization due to the solvent-dependent crystallographic packing in the co-crystals.…”

Supramolecular Fullerene Tetramers Concocted with Porphyrin Boxes Enable Efficient Charge Separation and Delocalization

“…Among these systems, porphyrin/fullerene supramolecular cocrystals with well-defined structures offer the opportunity to access precisely defined arrangements of the donor/acceptor sites, which in turn allows for examining the relationship between structure and function. However, although several porphyrin/fullerene cocrystals were reported, ,− their abilities to form charge-separated states (CSSs) were rarely studied , and ad hoc assemblies showed disappointingly short lifetimes of CSSs and low charge mobility. This poor performance might be due to most known constructs being made from individual porphyrin/fullerene stacks (Scheme a), where the donor/acceptor distances are too far to enable direct interactions that promote an efficient sequence of charge transport, separation, and delocalization. ,,− Thus, a rational design of crystalline porphyrin/fullerene-based artificial light-harvesting systems with a higher degree of hierarchicality to overcome above drawbacks remains challenging.…”