Manipulating intermolecular interactions for ultralong organic phosphorescence

Ultralong organic phosphorescence(UOP)materials have received considerable attention in the field of organic optoelectronics due to their long lifetime,high exciton utilization,large Stokes shift,and so on.Great advancements have been achieved through manipulating intermolecular interactions for high-performance UOP materials in recent years.This review will discuss the influence of various intermolecular interactions,includingπ-πinteractions,n-πinteractions,halogen bonding,hydrogen bonding,coordinative bonding,and ionic bonding on phosphorescent properties at room temperature,respectively.We summarize the rule of manipulating intermolecular interactions for UOP materials with superior phosphorescent properties.This review will provide a guideline for developing new UOP materials with superior phosphorescent properties for potential applications in organic electronics and bioelectronics.

Asymmetric side-chain engineering of organic semiconductor for ultrasensitive gas sensing

Molecular structure of organic semiconductor plays a critical role in determining the performance and functionality of organic electronic devices,by optimizing the electrical,optical and physicochemical properties.Substituted alkyl chains are fundamental units in tailering the solubility and assemblability,among which the asymmetric properties have been reported as key element for controlling the packing motifs and intrinsic charge transport.Here,we expanded the scope of molecular asymmetry dependent sensing features based on a new series of naphthalene diimides(NDI)-based derivatives substituted with a same branching alkyl chain but various linear-shaped alkyl chains(Cn-).A clear molecular stacking change,from head-to-head bilayer to head-to-tail monolayer packing model,is observed based on the features of anisotropic molecular interactions with the change in the chain length.Most importantly,a unique LUMO level shift of 0.17 eV is validated for NDI-PhC4,providing a record sensitivity up to 150%to 0.01 ppb ammonia,due to the desired molecular reactivity and device amplification properties.These results indicate that asymmetric side-chain engineering opens a route for breath healthcare.

Organic molecular aggregates:From aggregation structure to emission property

Organic molecular aggregates have attracted widespread attention over the past decade owing to their unique optoelectronic properties in the aggregate state,which mainly involves the effects of aggregation structure as well as molecular packing mode.Although many examples of H-and J-aggregates defined by molecular exciton model have been found,there are also other types of unconventional aggregates,especially for aggregation-induced emission(AIE)system.In this review,the recent progress of some examples of basic and novel aggregate forms,as well as coassembled forms,presenting distinctive optical features,such as optical waveguide and polarization emission,polymorph-dependent emission and stimuli-responsive luminescence are presented.The systematic insight into the relationship between the aggregation structure and emission property is discussed.Guidelines are therefore anticipated and will direct the future preprogramming molecular design so as to fine-tune the emission feature through a specific aggregation model for developing organic molecular aggregates with desirable optoelectronic properties.

Negative effect on molecular planarity to achieve organic ternary memory: triphenylamine as the spacer

Adjusting the spacers between the electron-acceptor and the elector-donor is important to design organic ternary memory material but rarely reported. In this paper, two small molecules, ZIPGA and ZIPCAD with benzene ring or triphenylamine as the spacers, were designed and synthesized to fabricate memory devices. The A1/ZIPGA/indium-tin oxide （ITO） device showed ternary characteristics, whereas A1/ZIPCAD/ITO had no obvious memory characteristics. Density functional theory calculation, X-ray diffraction （XRD） and atomic force microscopy （AFM） were employed to interpret the different memory properties. ZIPGA thin film has the closer intermolecular packing and flatter surface morphology than ZIPCAD film, which was favorable to the electron migration. This work demonstrates the importance of spacers and reveals that triphenylamine may be not a good spacer in design of new memory material.

Single-bond-linked oligomeric donors for high performance organic solar cells

The effective design and synthesis of novel small-molecule donors(SMDs) is extremely essential for the in-depth study of the scientific problems of bulk heterojunction morphology and the improvement of photovoltaic performance in organic solar cells(OSCs). Importantly, developing a series of donors with different conjugated central donor(D) units is a remarkable strategy to obtain high-performance donors. Herein, two acceptor-donor-donor-acceptor(A-D-D-A) type oligomeric donors 2DTBDT and2DTBDT-2T with two dithieno[2,3-d:2,3-d’]benzo[1,2-b:4,5-b’]dithiophene(DTBDT) as D units, without and with bithiophene as the π bridge respectively are designed and synthesized successfully. The central linked-DTBDT unit can provide a larger conjugated plane and promote π electron delocalization, which can effectively improve π-π interactions between donors and regulate the crystallinity. And we found that the π bridge provided 2DTBDT-2T with 12.31% efficiency that is already a high efficiency in OSCs,whereas 2DTBDT with merely 3.63% efficiency, both with 2,2-((2Z,2 Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2,"3 ’:4,5 ]thieno[2,3 :4,5]pyrrolo[3,2-g]thieno-[2,3 :4,5]thieno[3,2-b]indole,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile(Y6) as the acceptor. We conjecture that the main reason for the different device performance may be ascribed to the different molecular stacking orientation of the oligomeric donors and morphology features of the donors:Y6 blend films. Compared to the predominant face-on orientation of the 2DTBDT neat film, the 2DTBDT-2T neat film performed a preferential edge-on orientation, which obtained a smoother surface, stronger crystallinity and more uniform phase separation in the 2DTBDT-2T:Y6 blend films with nanofiber structure, which delivered higher and more balanced carrier mobilities, the more efficient exciton dissociation and reduced biomolecule recombination, therefore obtaining better power conversion efficiencies(PCEs). We speculate that the transformation of molecular stacking orientation of oligomeric donors is possibly due to that π bridge extended and twisted the molecular structure of 2DTDBT-2T, resulting in an edge-on orientation relative to the substrate. These findings demonstrate that the single-bond-linked donor strategy is an alternative method to design the donors towards high-performance OSCs.

Photodimerization-induced transition of helixes to vesicles based on coumarin-12-crown-4

Rational construction of fine-tuning and precisely controllable topological nanostructures based on supramolecular self-assembly system remains a challenge.Herein,coumarin-12-crown-4(1)as a building block was synthesized by one-pot method and showed reversible high stereo-selective photodimerization(anti-head-to-head dimer(anti-HH-1):syn-head-to-head dimer(syn-HH-1)=10.8:1)and photocleavage.Helical nanobelts were formed by the self-assembly of 1 through asymmetrical H-bonds,which were in concordance with the crystal state superstructure.Upon irradiation with 365 nm light,these nanobelts transformed into nanoballs which were constructed by three building blocks.Further,we investigated the photoreaction of 1 and got two pure covalent dimers(anti-HH-1 and syn-HH-1).The anti-HH-1 selfassembled into hollow micro-vesicles.The transformation of superstructures based on photo-controlled multiple blocks shines a light to the research on the relationship between molecules and superstructures.