Saddle‐Shaped Building Blocks: A New Concept for Designing Fully Conjugated 3D Organic Semiconducting Materials

Abstract

Currently, most organic semiconducting materials (OSMs) are π‐conjugated structures in one or two dimension (2D), where the lack of layer‐layer π‐conjugation connection greatly blocks their electron delocalization and transport. The 3D fully conjugated materials could solve this issue because they can provide efficient charge‐transport pathways throughout the whole 3D skeleton, in which the suitable 3D building block is the key to the development of fully conjugated 3D OSMs. Cyclooctatetraene (COT) and its derivatives are good candidates due to their π‐conjugation with 3D saddle‐shaped architecture. In this Concept, we discuss the key features of saddle‐shaped COT‐based derivatives and their synthetic strategy, then we present the current development of using the COT derivatives as building blocks to construct the 3D fully conjugated organic small compound‐ and polymer‐based OSMs. The properties and perspectives of these OSMs in photovoltaics, electro‐catalysis and electrical conductivities are also discussed. These recent advances in the developing 3D fully conjugated materials could potentially open up a new frontier in the design of OSMs.

A Conjugated Figure‐of‐Eight Oligoparaphenylene Nanohoop with Adaptive Cavities Derived from Cyclooctatetrathiophene Core

“…In addition, the sum of local delocalization in 20 benzene and 4thiophene units is 113.9 electrons composed of 101.6 p and 12.3 s electrons (Figure 5). Thus,the conjugation between adjacent benzene or thiophene units can be calculated as (134.6 e/13.9 e)/26 = 0.80 e, where 26 is the number of the formal CÀCs ingle bonds of 1.T his result is comparable with the EDDB results of [8]CPP (0.84 e) and its derivative (0.81 e) in the literature. [22] Furthermore,t here is minor influence of host-guest interactions on the conjugation, supported by the almost same delocalized electrons of nanohoops and fullerenes in C 60 @1,2 C 60 @1,C 70 @1,a nd 2C 70 @1 (Figures S46-S55).…”

“…COThh as saddle-shaped non-planar conjugation in which the diagonal thiophene moieties can be amenable to flexible conformations. [8] We envisioned that fusing COThand oligoparaphenylene would construct afully conjugated molecule with intriguing topology that hybridizes structural rigidity and flexibility.I ts lemniscular skeleton would maintain strained yet pliable dual cavities surrounded by three-dimensional interlocked p-surfaces. [6c, 9] Indeed, molecule 1 exhibits adaptive binding to fullerenes C 60 and C 70 .…”

Designing Thiophene‐Enriched Fully Conjugated 3D Covalent Organic Framework as Metal‐Free Oxygen Reduction Catalyst for Hydrogen Fuel Cells

“…Considering the fact that thiophene rings are very commonly used in organic semiconducting materials as they can significantly promote the charge transfer and improve electrocatalytic efficiency, [7b, 15] and inspired by our previous work that uses the saddle‐shaped cyclooctatetrathiophene derivative [16] (COThP‐CHO, chemical structure see Scheme 1a) as a building block to construct fully conjugated 3D COFs, [5b, 11a, c] here we design an all‐thiophene‐connected saddle‐shaped conjugated building block (COThTh‐CHO, Scheme 1a, Scheme S1) and successfully synthesize a thiophene‐enriched fully conjugated 3D COF (BUCT‐COF‐11). Benefited from the extended π‐conjugated and thiophene‐rich structures, BUCT‐COF‐11 exhibited intrinsic metal‐free ORR electrocatalytic activity.…”

Post-synthetic Fully π-Conjugated Three-Dimensional Covalent Organic Frameworks for High-Performance Lithium Storage

“…Rare examples have been reported in making fully π-conjugated 3D COFs. Compared to the commonly reported 2D COFs, 3D COFs have been less extensively studied due to the synthetic challenge and difficult structure determination. − In addition, not like 2D COFs, the “unavoidable” presence of the unconjugated tetrahedral building blocks such as tetraphenylmethane and tetraphenylsilane moieties which are based on sp 3 -hybridized carbon or silane has hindered the design of conjugated systems. − The fully π-conjugated characteristics of the linkers and linkages are both indispensable for the construction of fully π-conjugated 3D COFs, which is challenging in constructing fully conjugated 3D COF materials. − Recently, a strategy to prepare 3D COFs with the combination of trigonal planar and square planar units was reported by Yaghi, Zhao, and Cui . These fascinating results indicated that tetrahedral building blocks were no longer necessary and a large number of “[3 + 4]” 3D COFs may emerge considering the prevalently used trigonal planar and square planar building blocks.…”