Organic Donor–Acceptor Complexes as Novel Organic Semiconductors

Abstract

Organic donor-acceptor (DA) complexes have attracted wide attention in recent decades, resulting in the rapid development of organic binary system electronics. The design and synthesis of organic DA complexes with a variety of component structures have mainly focused on metallicity (or even superconductivity), emission, or ferroelectricity studies. Further efforts have been made in high-performance electronic investigations. The chemical versatility of organic semiconductors provides DA complexes with a great number of possibilities for semiconducting applications. Organic DA complexes extend the semiconductor family and promote charge separation and transport in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In OFETs, the organic complex serves as an active layer across extraordinary charge pathways, ensuring the efficient transport of induced charges. Although an increasing number of organic semiconductors have been reported to exhibit good p- or n-type properties (mobilities higher than 1 or even 10 cm V s), critical scientific challenges remain in utilizing the advantages of existing semiconductor materials for more and wider applications while maintaining less complicated synthetic or device fabrication processes. DA complex materials have revealed new insight: their unique molecular packing and structure-property relationships. The combination of donors and acceptors could offer practical advantages compared with their unimolecular materials. First, growing crystals of DA complexes with densely packed structures will reduce impurities and traps from the self-assembly process. Second, complexes based on the original structural components could form superior mixture stacking, which can facilitate charge transport depending on the driving force in the coassembly process. Third, the effective use of organic semiconductors can lead to tunable band structures, allowing the operation mode (p- or n-type) of the transistor to be systematically controlled by changing the components. Finally, theoretical calculations based on cocrystals with unique stacking could widen our understanding of structure-property relationships and in turn help us design high-performance semiconductors based on DA complexes. In this Account, we focus on discussing organic DA complexes as a new class of semiconducting materials, including their design, growth methods, packing modes, charge-transport properties, and structure-property relationships. We have also fabricated and investigated devices based on these binary crystals. This interdisciplinary work combines techniques from the fields of self-assembly, crystallography, condensed-matter physics, and theoretical chemistry. Researchers have designed new complex systems, including donor and acceptor compounds that self-assemble in feasible ways into highly ordered cocrystals. We demonstrate that using this crystallization method can easily realize ambipolar or unipolar transport. To further improve device performance, we propose several design strategies, such a...

A Facile Molecular Machine: Optically Triggered Counterion Migration by Charge Transfer of Linear Donor‐π‐Acceptor Phosphonium Fluorophores

“…[29] Thedication 9 shows two 31 Ps ignals (d = 23.4 and 22.0 ppm) because of the presence of two inequivalent Pn uclei, which demonstrate distinct long-range magnetic coupling ( 4 J P-P = 9.9 Hz). [30] Thec ompounds demonstrate high thermal stability according to TGA analysis ( Figure S2); with aminimum weight loss up to 300 8 8Cfor selected salts (2,4,5,8). [30] Thec ompounds demonstrate high thermal stability according to TGA analysis ( Figure S2); with aminimum weight loss up to 300 8 8Cfor selected salts (2,4,5,8).…”

“…[1] Thus,i ti sn ot surprising that donor-acceptor compounds hold aprominent position in materials science [2] and have been extensively used in organic electronics,i np articular for the development of organic electroluminescent devices, [3] solar cells, [4] field-effect transistors, [5] and nonlinear optical materials. [1] Thus,i ti sn ot surprising that donor-acceptor compounds hold aprominent position in materials science [2] and have been extensively used in organic electronics,i np articular for the development of organic electroluminescent devices, [3] solar cells, [4] field-effect transistors, [5] and nonlinear optical materials.…”

Mixed stack charge transfer crystals: Crossing the neutral-ionic borderline by chemical substitution

“…Mixed stack CT crystals are then characterized by an intriguing phenomenology that includes multiple competing phases, divergent response, and anomalous metallic states [9]. From the perspective of materials research, several application oriented aspects are being pursued, that span from organic semiconductivity and photovoltaic [10,11], to ultrafast photoswitching [12], to ferroelectrics [13], to cite a few.…”

Organic Cocrystals: Beyond Electrical Conductivities and Field‐Effect Transistors (FETs)

“…Hydrogen bonds are stable and can present good orientation to help predict the structural consequences much more easily. [1,37,42,43] [1,37,42,43] …”

“…[4] However,t here are long-standing critical problems in this research field. [5,36] There are some excellent reviews about organic D-A complexes for novel organic electronics [37] and techniques/ methods of the preparation and characterization of organic cocrystals,a sw ell as some applications of cocrystals before 2016, [38a] thus in this Minireview,w eo nly make ab rief summary focusing on recent development and applications (except electrical conductivities and field-effect transistors (FETs)) of organic cocrystals including reducing the ACQ effect, tuning light emission, ferroelectricity and multiferroics, optical waveguides,a nd stimuli-responsiveness.W ea lso provide ad iscussion on current achievements,l imitations and perspectives.F inally,w et ry to aim at providing some useful instructions for further investigation of organic cocrystals. Secondly,t he relationships between crystal structures and the resulting performance,between the charge-transfer degree within cocrystals and the lattice stability, [33] optoelectronic,and photophysical properties, [34,35] as well as the mechanism of electronic interaction between building blocks remain elusive, [5] all of which greatly impedes regulating the properties of the cocrystals.T he effective tuning of cocrystals properties to give the desired functions by designing and controlling the stoichiometric ratio,m olecular stacking mode,o rientation, crystal phase and morphology is still at an early stage and remains achallenge.…”