Growth onset of perylene-based nanocrystals

The wide application of organic nanocrystals requires a deeper understanding of their nucleation mechanisms. In particular, the onset of nucleation still needs to be elucidated, although tremendous efforts have already been made in both experimental and simulation studies. In this research, we conduct molecular dynamics (MD) simulations, supported by quantum mechanical (DFT) calculations, to understand the mechanisms of the nucleation onset of organic perylene nanocrystals. Our DFT calculations indicate that face-to-face and face-to-edge molecular stacking can ultimately lead to the formation of a herringbone-style perylene nanocrystal. On the other hand, the results of MD simulations show the formation of clusters, which continues with the crystal nucleation in the form of unidirectional or multidirectional growth, depending on the feeding rate of perylene molecule in vacuum. This research helps to better understand the control of the growth of organic nanocrystals in modern nanotechnology.

Metal Complexes of π-Expanded Ligands (8): Cold Crystallization of bis[2-[(octylimino)methyl]-1-pyrenolato-N,O] copper(II) by Thermal Analyses, Magnetic Studies, and FT-IR

Molecules exhibiting cold crystallization, an exothermic phenomenon in heating following supercooling, can be used as a heat-storing material. On the other hand, examples in non-polymers are still few. To test metal complexes as potential compounds for heat-storage materials, a salicylaldiminato-typed copper(II) complex, bis[2-[(octylimino)methyl]-1-pyrenolato-N,O] copper(II) 1(Cu), which had two different coloured forms and a characteristic long alkyl chain, exhibited complicated thermal behaviour including cold crystallization. The long alkyl chain was a steric barrier to molecular stacking, leading to the supercooled state. Besides, the two polymorphs were characterized by IR spectra studies and magnetic susceptibility.

A comprehensive nano-interpenetrating semiconducting photoresist toward all-photolithography organic electronics

Owing to high resolution, reliability, and industrial compatibility, all-photolithography is a promising strategy for industrial manufacture of organic electronics. However, it receives limited success due to the absence of a semiconducting photoresist with high patterning resolution, mobility, and performance stability against photolithography solution processes. Here, we develop a comprehensive semiconducting photoresist with nano-interpenetrating structure. After photolithography, nanostructured cross-linking networks interpenetrate with continuous phases of semiconducting polymers, enabling submicrometer patterning accuracy and compact molecular stacking with high thermodynamic stability. The mobility reaches the highest values of photocrosslinkable organic semiconductors and maintains almost 100% after soaking in developer and stripper for 1000 min. Owing to the comprehensive performance, all-photolithography is achieved, which fabricates organic inverters and high-density transistor arrays with densities up to 1.1 × 105 units cm−2 and 1 to 4 orders larger than conventional printing processes, opening up a new approach toward manufacturing highly integrated organic circuits and systems.

Design of All-Small-Molecule Organic Solar Cells Approaching 14% Efficiency via Isometric Terminal Alkyl Chain Engineering

Morphology is crucial to determining the photovoltaic performance of organic solar cells (OSCs). However, manipulating morphology involving only small-molecule donors and acceptors is extremely challenging. Herein, a simple terminal alkyl chain engineering process is introduced to fine-tune the morphology towards high-performance all-small-molecule (ASM) OSCs. We successfully chose a chlorinated two-dimension benzo[1,2-b:4,5-b′]dithiophene (BDT) central unit and two isomeric alkyl cyanoacetate as the end-capped moieties to conveniently synthesize two isomeric small-molecule donors, namely, BT-RO-Cl and BT-REH-Cl, each bearing linear n-octyl (O) as the terminal alkyl chain and another branched 2-ethylhexyl (EH) as the terminal alkyl chain. The terminal alkyl chain engineering process provided BT-RO-Cl with 13.35% efficiency and BT-REH-Cl with 13.90% efficiency ASM OSCs, both with Y6 as the electron acceptor. The successful performance resulted from uniform phase separation and the favorable combination of face-on and edge-on molecular stacking of blended small-molecule donors and acceptors, which formed a fluent 3D transport channel and thus delivered high and balanced carrier mobilities. These findings demonstrate that alkyl chain engineering can finely control the morphology of ASM OSCs, and provides an alternative for the optimal design of small-molecule materials towards high-performance ASM OSCs.

Both Symmetric and Asymmetric Electro-Optic Dynamic Behavior with SSD (Smectic Single Domain) Liquid Crystals

SSD-liquid crystal panels’ retardation switching dynamic behaviors have been investigated from their in-plane and out-of-plane retardation switching behaviors. In-plane-only and a mixture between in-plane and out-of-plane retardation switching behaviors are highly related to the initial smectic liquid crystal molecular stacking configurations. With uniformly stacked configuration, a completely symmetric retardation switching, as well as light throughput behavior, was obtained. With a slight twisted stacking configuration, the retardation switching behavior is dependent on the applied electric field strength, which may change the initial molecular stacking configuration, resulting in either symmetric or asymmetric retardation switching. When the molecular stacking has twisted heavily, the obtained retardation switching showed asymmetric behavior regardless of the applied electric field strength.

Unusual piezochromic fluorescence of a distyrylpyrazine derivative crystals: phase transition through [2 + 2] photocycloaddition under UV irradiation

The piezochromic fluorescence (FL) of a distyrylpyrazine derivative, 2,3-diisocyano-5,6-distyrylpyrazine (DSP), was investigated in this study. Depending on the recrystallization method, DSP afforded two different crystals with green and orange FL emission. The orange color FL emission crystal (O-form) was easily converted to the green color FL emission one (G-form) by manual grinding. The G-form was also converted to a slightly different orange color FL emission crystal (RO-form) by a weak UV irradiation. When the RO-form was ground again, the G-form was regenerated. The FL colors changed between the G- and RO-forms over several ten times by repeated mechanical grinding and UV irradiation. The FL, UV–visible, 1H-NMR and XRD results showed that the O (or RO)-to-G transformation induced by mechanical stress results from the change of degree of molecular stacking from dense molecular stacking structure to relatively loose molecular stacking structure, whereas the G-to-RO reconversion by UV irradiation results from return to dense molecular stacking structure again due to lattice movement (lattice slipping) allowed by photocycloaddition in solid-state.

Comprehensive understanding of the structure-stacking property correlation to achieve high-performance ternary data-storage devices

Two small-molecule isomers with consistent functional units exhibit total different molecular stacking modes, rendering the memory behaviours from traditional binary memory to typical ternary memory.

Ala–Ala dipeptides with a semi-perfluoroalkyl chain: chirality driven molecular packing difference and self-assembly driven chiral transfer

The chirality of amino acids triggered the chiral molecular stacking of dipeptides and, eventually, transferred to the semi-perfluoroalkyl chain.