Chemically Driven Interfacial Coupling in Charge-Transfer Mediated Functional Superstructures

Abstract

Organic charge-transfer superstructures are enabling new interfacial electronics, such as organic thermoelectrics, spin-charge converters, and solar cells. These carbon-based materials could also play an important role in spin-based electronics due to their exceptionally long spin lifetime. However, to explore these potentials a coherent design strategy to control interfacial charge-transfer interaction is indispensable. Here we report that the control of organic crystallization and interfacial electron coupling are keys to dictate external stimuli responsive behaviors in organic charge-transfer superstructures. The integrated experimental and computational study reveals the importance of chemically driven interfacial coupling in organic charge-transfer superstructures. Such degree of engineering opens up a new route to develop a new generation of functional charge-transfer materials, enabling important advance in all organic interfacial electronics. KEYWORDS: Nanoferroics, organic crystallization, materials design, and multifuctionality T he mixing of conductivity and ferroic orders in functional materials could lead to numerous technological advances, such as ferroic field-effect transistors and magnetoelectric tunnel junctions. 1−4 However, the ferroic orders are related to the interaction of localized electrons while the conduction is determined by the movement of electrons; thus, simultaneous conducting and ferroic orders remains challenging in conventional materials. Materials-by-design and assembly principle provides a unique and exciting opportunity, as it allows us to design novel multifunctional organic materials that combine two or more physical properties in the same crystal lattice, which are difficult or impossible to achieve in continuous inorganic crystalline solids. Organic charge transfer (CT) assemblies, consisting of an electron donor and acceptor with π-electron orbitals, can possess both charge and spin orders due to the largely delocalized π-electrons and the exchange interaction. 5,6 Over the past decades, numerous materials have been designed toward the development of functional CT complexes. 7,8 Recently, room-temperature multiferroicity in centimeter-sized crystalline charge-transfer superstructures, consisting of polymer−fullerene complexes, was achieved by the self-organization and molecular-packing induced charge order-driven ferroic coupling. 9 To take advantage of the complexity and tunability of this new class of organic functional materials, a comprehensive understanding of the relationship between structure and properties is important.Interfacial engineering has been widely used to tune the electronic and optical behaviors of polymer−fullerene-based CT devices, and materials-by-design criteria exhibit a strong dependence on their structural architecture as demonstrated by both experimental 10−14 and theoretical 15−19 studies. Typically, longer side chain lengths of polymers lead to higher fullerene mobility and thus a larger scale of phase separation that reduces the ...

Tunable two-dimensional interfacial coupling in molecular heterostructures

“…In this context, the urgent demand of flexible nanoelectronics and optoelectronics calls for a novel generation of organic heterostructures held by vdW forces for both vertical and horizontal orientation 6 , 7 . Among the organic complexes, the superior optoelectronic properties and the lack of interlayer screening effect for the 2D donor and acceptor CT molecular crystals, as well as the charge density wave induced long-range vdW force in the polarized structure, is a promising candidate to enable 2D CT molecular heterostructures with tunable optical–electronic–magnetic coupling behavior at the atomic level 8 – 17 .…”

Organic Donor‐Acceptor Cocrystals for Multiferroic Applications

“…[4][5][6] More importantly, the controllable polar dimerization by the longrange supramolecular ordering interactions and spin density wave within tightly packed CT lattices in CTC has offered a promising pathway to endow them with ferroelectric or ferromagnetic properties. [72][73] For instance, the canonical mixed-stack CT system, tetrathiafulvalene (TTF) with halogenated quinones, e. g., TTF • chloranil (TTF • CA), undergoes a ferroelectric phase transition (ionic/ferroelectric phase) owing to the molecular displacement and rearrangement of the molecularcharge distribution along the CT chain. [24,[74][75] Besides, CT crystals with ferroelectric Curie temperature above room temperature based on a pyromellitic diimide-based acceptor and derivatives of naphthalene-, pyrene-and TTF-based donors have also been developed, which is critical for the practical application.…”

“…[33] Another typical C 60 -based CT multiferroics system is the family of thiophene-based compounds, where thiophene acts as the electron-donating moiety. [29][30]32,72,77] For instance, by co- assembling thiophene donor and C acceptor together into athree-dimensional CTC with a hierarchical organization and long-range noncovalent interactions (segregated-stack), a remarkable anisotropic magnetization and room temperature multiferroicity can be achieved. [29] In this system, the ferromagnetism likely originates from the unpaired spin alignment within charged thiophene nanowires induced by the charge transfer.…”

“…[30] Similar phenomena are also observed in the donor-acceptor segregated-stack CT cocrystals based on fullerene and other thiophene-based derivatives. [72,77] To be mentioned, a magnetoelastic character can also be realized in this polythiophene (P3HT) • C 60 system, where the saturation magnetization varies inversely with the applied static compression stress. Such external mechanical field-dependent magnetization is the result of the coupling between magnetization and macroscopic deformation mediated by charge density waves.…”

Coarse graining a non-Markovian collisional model

“…Recent theoretical [7][8][9][10][11][12][13][14][15] and experimental [16][17][18][19][20][21][22][23][24][25] works have demonstrated how to use the so-called collisional models to simulate generic non-unitary dynamics [7,8] and, specifically, to better understand the emergence of non-Markovian effects [9][10][11][12][13][14][15]. Collisional models are those in which the environment is made of particles that randomly collide with the system, usually one at a time, generating non-unitary dynamics.…”