Supramolecular Design of Donor-Acceptor Complexes via Heteroatom Replacement toward Structure and Electrical Transporting Property Tailoring

Structural effect of NIR-II absorbing charge transfer complexes and its application on cysteine-depletion mediated ferroptosis and phototherapy

Second near-infrared (NIR-II) absorbing organic photothermal agents (PTAs) usually suffer from laborious and time-consuming synthesis; therefore, it is of importance to develop a simple and easy-to-handle method for the preparation of NIR-II PTAs. Charge-transfer complexes (CTCs) can be easily used to construct NIR-II absorbing PTAs, although the relationship between their molecular structure and photophysical properties is yet to be uncovered. Herein, three kinds of electron donors with different substitutions (chloroethyl, ethyl, and methyl) were synthesized and assembled with electron-deficient F4TCNQ to afford corresponding CTC nanoparticles (Cl-F4, Et-F4, and Me-F4 NPs). The large energy gap (>0.61 eV) between HOMO of the donor and LUMO of the acceptor made the CTCs exhibit high charge transfer (>0.93) and dramatic differences in photophysical properties. Additionally, Et-F4 NPs possess the highest NIR-II absorption ability and best photothermal effect because of different packing modes (mass extinction coefficient of 11.0 L g^-1 cm^-1 and photothermal conversion efficiency of 40.2% at 1060 nm). The mixed stacking mode formed strong charge-transfer absorption bands, indicating that the photophysical properties of CTCs can be tailored by changing the molecular structure and aggregate behaviors. Furthermore, Et-F4 NPs with cyano groups could specifically react with cysteine to block the intracellular biosynthesis of GSH and result in ROS accumulation and ferroptosis. Et-F4 NPs possess outstanding antitumor efficacy for the combined actions of NIR-II triggered photothermal killing effect and ferroptosis in vivo.

Functional Carbazole-Fullerene Complexes: A New Perspective of Carbazoles Acting as Nano-Octopus to Capture Globular Fullerenes

Fullerene host-guest constructs have attracted increasing attention owing to their molecular-level hybrid arrangements. However, the usage of simple carbazolic derivatives to bind with fullerenes is rare. In this research, three novel carbazolic derivatives, containing a tunable bridging linker and carbazole units for the capturing of fullerenes, are rationally designed. Unlike the general concave-convex interactions, fullerenes could interact with the planar carbazole subunits to form 2-dimensional hexagonal/quadrilateral cocrystals with alternating stacking patterns of 1 : 1 or 1 : 2 stoichiometry, as well as the controllable fullerene packing modes. At the meanwhile, good electron-transporting performances and significant photovoltaic effects were realized when a continuous C_60⋅⋅⋅ C₆₀ interaction channel existed. The results indicate that the introduction of such carbazolic system into fullerene receptor would provide new insights into novel fullerene host-guest architectures for versatile applications.

Fast Delayed Emission in New Pyridazine-Based Compounds

Three novel donor-acceptor molecules comprising the underexplored pyridazine (Pydz) acceptor moiety have been synthesized and their structural, electrochemical and photophysical properties thoroughly characterized. Combining Pydz with two phenoxazine donor units linked via a phenyl bridge in a meta configuration (dPXZMePydz) leads to high reverse intersystem crossing rate k RISC = 3.9 · 106 s-1 and fast thermally activated delayed fluorescence (TADF) with <500 ns delayed emission lifetime. Efficient triplet harvesting via the TADF mechanism is demonstrated in OLEDs using dPXZMePydz as the emitter but does not occur for compounds bearing weaker donor units.

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

The recent progress of charge-transfer complexes (CTCs) for application in many fields, such as charge transport, light emission, nonlinear optics, photoelectric conversion, and external stimuli response, makes them promising candidates for practical utility in pharmaceuticals, electronics, photonics, luminescence, sensors, molecular electronics and so on. Multicomponent CTCs have been gradually designed and prepared as novel organic active semiconductors with ideal performance and stability compared to single components. In this review, we mainly focus on the recently reported development of various charge-transfer complexes and their performance in field-effect transistors, light-emitting devices, lasers, sensors, and stimuli-responsive behaviors.

Fast Crystallization-Deposition of Orderly Molecule Level Heterojunction Thin Films Showing Tunable Up-Conversion and Ultrahigh Photoelectric Response

Molecular cocrystals have received much attention for tuning physicochemical properties in pharmaceutics, luminescence, organic electronics, and so on. However, the effective methods for the formation of orderly cocrystal thin films are still rather limited, which have largely restricted their photofunctional and optoelectronic applications. In this work, a fast crystallization-deposition procedure is put forward to obtain acridine (AD)-based cocrystals, which are self-assembled with three typical isophthalic acid derivatives (IPA, IPB, and TMA). The obtained donor-acceptor cocrystal complexes exhibit an adjustable energy level, wide range of photoluminescence color, and rotational angle-dependent polarized emission. The orderly and uniform cocrystal thin films further present tunable one-/two-photon up-conversion and different semiconductor properties. Particularly, AD-TMA cocrystal thin film shows a rare example of a molecule level heterojunction with the alternating arrangement of AD electronic acceptor layers and TMA electronic donor layers, and thus, provides a way for efficient mobility and separation of electron-hole pairs. A large on-off photocurrent ratio of more than 104 can be achieved for the AD-TMA thin film, which is higher than state-of-the-art molecular semiconductor systems. Therefore, this work extends the application scopes of orderly cocrystal thin film materials for future luminescent and optoelectronic micro-/nanodevices.

Nucleation Control-Triggering Cocrystal Polymorphism of Charge-Transfer Complexes Differing in Physical and Electronic Properties

Binary charge-transfer complex polymorphs composed of perylene and 4,8-bis(dicyanomethylene)-4,8-dihydrobenzo-[1,2-b:4,5-b']-dithiophene (DTTCNQ) were synthesized separately via a simple artificial nucleation-tailoring method, in both macroscopic and microscopic cocrystal engineering manners. The two polymorphs were testified to be independently thermosalient in the solid state, and the specific self-assembly derived from homogeneous or heterogeneous nucleation by assistance of governable thermodynamic/kinetic drive, leading to a change in the ordered p-n stacking structure. The as-prepared polymorphic microcrystals afforded a significantly varied (opto)electronic property: high n-type transporting and good photoresponsivity for β-complex, and ambipolar transporting with ignorable photoresponsivity for α-complex, attributing to the different charge-transfer and supramolecular alignment. This work provides us a new route to the exploitation of donor-acceptor complex family, making it possible to develop functional materials and devices based on variable supramolecular binary structures.

Pentacene derivative/DTTCNQ cocrystals: alkyl-confined mixed heterojunctions with molecular alignment and transport property tuning

Soluble pentacene-based complexes were successfully prepared and short contact interactions induced alignment driving forces to eliminate C/S disorders. Cocrystal packing and charge transport properties were tailored by adjusting the solvent.

Organic cocrystals are formed via the self-assembly of donor and acceptor constituents, which are mixed together through weak noncovalent interactions. Although they reveal unique physical features, their synthesis still faces major drawbacks for the introduction of more potential semiconductors. Herein, we first report soluble pentacene derivative (TMTES-P) based complexes, with suitable alkyl terminal groups, enabling the location of 4,8-bis(dicyanomethylene)-4,8-dihydrobenzo[1,2-b:4,5-b′]-dithiophene (DTTCNQ) in the crystal lattice, thereby allowing the cocrystallization of a binary system on demand. To our surprise, via varying growth conditions, molecular disorders could be removed due to existing short-contacts as the locking force, and even the carrier charge could be changed. This organic donor–acceptor system presents unconventional insights: charge polarity control over (opto)electronic devices with a supramolecular driving force as the directional alignment guide.