Langmuir-Blodgett Thin Films of Diketopyrrolopyrrole-Based Amphiphiles

Near Infrared-II Excited Triplet Fusion Upconversion with Anti-Stokes Shift Approaching the Theoretical Limit

The anti-Stokes shift represents the capacity of photon upconversion to convert low-energy photons to high-energy photons. Although triplet exciton-mediated photon upconversion presents outstanding performance in solar energy harvesting, photoredox catalysis, stereoscopic 3D printing, and disease therapeutics, the interfacial multistep triplet exciton transfer leads to exciton energy loss to suppress the anti-Stokes shift. Here, we report near infrared-II (NIR-II) excitable triplet exciton-mediated photon upconversion using a hybrid photosensitizer consisting of lead sulfide quantum dots (PbS QDs) and new surface ligands of thiophene-substituted diketopyrrolopyrrole (Th-DPP). Under 1064 nm excitation, this photon upconversion revealed a record-corrected upconversion efficiency of 0.37% (normalized to 100%), with the anti-Stokes shift (1.07 eV) approaching the theoretical limit (1.17 eV). The observation of this unexpected result is due to our discovery of the presence of a weak interaction between the sulfur atom on Th-DPP and Pb2+ on the PbS QDs surface, facilitating electronic coupling between PbS QDs and Th-DPP, such that the realization of triplet exciton transfer efficiency is close to 100% even when the energy gap is as small as 0.04 eV. With this premise, this photon upconversion as a photocatalyst enables the production of standing organic gel via photopolymerization under 1064 nm illumination, displaying NIR-II photon-driven photoredox catalysis. This research not only establishes the foundation for enhancing the performance of NIR-II excitable photonic upconversion but also promotes its development in photonics and photoredox catalysis.

Supramolecular Control of Photonic Response and Sensing of Nitricoxide using Iron(III) Corrole Monolayers and Their Stacks

In this work, we assemble amphiphilic iron(III) corroles at air-water interfaces into well-defined quasi-two-dimensional molecular monolayers and theirs stacks for sensing of nitric oxide (NO). For this purpose, we use the Langmuir-Blodgett (LB) technique, which allows varying the packing density of iron(III) corroles anchored to the aqueous subphase via one molecular side. The stacks of ten down to three molecular monolayers on the front and back sides of the substrates are sufficiently optically dense to detect NO binding to the layers photometrically. This sensing with few layers demonstrates the potential for electronic detection, where very thin surface functionalizations enable efficient electronic communication between the layer and the (semi)conductor. Despite increasing optical densities, the spectral responses to NO exposure become smaller with increasing packing density until the collapse point of the monolayers is reached. This demonstrates that the highest molecular efficiency for binding and detection of NO is achieved at the smallest packing densities. This finding is relevant to all molecular sensor films with axial binding of analytes to the sensor molecules and demonstrates the advantage of sensor molecule assembly into monolayers on water-air interfaces using the LB technique.

A Novel Donor-Acceptor Thiophene-Containing Oligomer Comprising Dibenzothiophene-S,S-dioxide Units for Solution-Processable Organic Field Effect Transistor

A π-conjugated thiophene-containing oligomer with a D-A-D-A-D (D: donor, A: acceptor) architecture, namely, 2,6-bis{[4-(7-n-hexylthiophen-2-yl)thiophen-2-yl]-(dibenzothiophene-5,5-dioxide-3,3΄-diyl)}-bis((2-ethyl-hexyl)oxy)benzo[1,2-b:4,5-b’]dithiophen (BDT(DBTOTTH)₂), was synthesized by Stille coupling reactions. There are obvious shifts in the Ultraviolet-visible (UV-vis) and photoluminescence (PL) spectra of the thin film relative to its solution, indicating the existence of the π-π stacking in the solid state of the oligomer BDT(DBTOTTH)₂. The optical band gap of the oligomer determined from its absorption onset in UV-Vis spectra is 2.25 eV. It agrees with the value of 2.29 eV determined from the cyclic voltammetry (CV) measurement. Its highest occupied and lowest unoccupied molecular orbital (HOMO/LUMO) energy levels, which were calculated from its onset of oxidation and reduction waves in CV curve, are −5.51 and −3.22 eV, respectively. The oligomer is a P-type semiconductor material with a good thermal stability and solubility, which can be used to fabricate organic field effect transistors (OFETs) by the spin coating technique. The OFET with n-octadecanylltrichlorosilane (OTS)-modified SiO₂ dielectric layer exhibited a mobility of 1.6 × 10⁻³ cm²/Vs.

Layer-by-Layer Assembly of Monolayer Films Precisely Controlled by LB Technology to Realize Low-Energy Consumption and High-Stability Ternary Data-Storage Devices

Organic semiconductor devices with low energy consumption and excellent stability are highly desirable. Controlling the intermolecular alignment orientation by designing the molecular structure or optimization of the film preparation process is an alternative way to achieve this goal. In this paper, a new idea was proposed to realize the formation of an aligned monomolecular layer and multimolecular layer thin films on the electrode substrate by controlling the surface pressure of molecular layer on the liquid surface by LB technology. An amphiphilic π-conjugated D-A molecule was synthesized, and the influence of spin coating and LB technology on intermolecular ordered stacking in the film and the electrical memory performance were investigated. The results demonstrated that the film fabricated by LB technology has some advantages compared with that fabricated by spin-coating method, such as higher crystallinity, lower surface roughness and better-organized monomolecular and multimolecular layer, which significantly promoted the performance of the electrical memory device with lower power consumption and longer stability.

Langmuir-Blodgett Films of Diketopyrrolopyrroles with Tunable Amphiphilicity

In this work, we present the formation of H- and J-aggregates of amphiphilic centrosymmetric diketopyrrolopyrroles containing aliphatic or aromatic amino groups. The inherent amphiphilicity of these dyes predestines their assembly at interfaces to form ordered supramolecular structures. In this work, we employed the Langmuir-Blodgett (LB) technique to generate, manipulate, and deposit such supramolecular structures. The aforementioned amines provide an additional means to control the formation of the supramolecular assemblies. In the resulting LB films, both H- and J-aggregates of the dyes can be realized, leading to very broad absorption spectra. In contrast to many reports on H- and J-aggregates, the interactions between the symmetric diketopyrrolopyrroles are controlled via interface assembly and π-stacking and not by dipolar interactions. We show that in the case of the aliphatic, but not for the aromatic amine functionalization, the usage of an acidic subphase enables the transition from H- to J-aggregate-dominated LB films via an increase in the surface pressure during deposition.

Controlling n-Type Molecular Doping via Regiochemistry and Polarity of Pendant Groups on Low Band Gap Donor-Acceptor Copolymers

We demonstrate the impact of the type and position of pendant groups on the n-doping of low-band gap donor–acceptor (D–A) copolymers. Polar glycol ether groups simultaneously increase the electron affinities of D–A copolymers and improve the host/dopant miscibility compared to nonpolar alkyl groups, improving the doping efficiency by a factor of over 40. The bulk mobility of the doped films increases with the fraction of polar groups, leading to a best conductivity of 0.08 S cm^–1 and power factor (PF) of 0.24 μW m^–1 K^–2 in the doped copolymer with the polar pendant groups on both the D and A moieties. We used spatially resolved absorption spectroscopy to relate commensurate morphological changes to the dispersion of dopants and to the relative local doping efficiency, demonstrating a direct relationship between the morphology of the polymer phase, the solvation of the molecular dopant, and the electrical properties of doped films. Our work offers fundamental new insights into the influence of the physical properties of pendant chains on the molecular doping process, which should be generalizable to any molecularly doped polymer films.

Behavior of Muscle-Derived Stem Cells on Silica Nanostructured Substrates

The aim of the present work was to evaluate the responses of rat muscle-derived stem cells (rMDSCs) to growth on silica nanostructured substrates (SN) with nanoscale topographic surfaces. SN of different sizes (SN-60, SN-150, SN-300, SN-500, and SN-700) were prepared using silica nanoparticles with sizes of 60-700 nm. The prepared SN showed roughness at the nanoscale level. The total number of adherent cells on SN increased with increasing nanoscale level and incubation time. The rMDSCs attached to SN-500 and SN-700 were extensively flattened, whereas those grown on SN-60, SN-150, and SN-300 were more rounded. The rank order of the cell length and height of attached rMDSCs at 5 d on different surfaces was SN-60 ≈ SN-150 >> SN-300 > SN-500 > SN-700 > glass. Compared with rMDSCs grown on SN-60, SN-150, or SN-300, those attached to SN-500 and SN-700 exhibited a distinct morphology with filopodial extensions and stronger expression of focal adhesion, integrin, and actin. An evaluation of the gene expression of adhered rMDSCs showed that rMDSCs grown on SN-300 exhibited a higher environmental stress response than those grown on glass or SN-700. Collectively, our data provide fundamental insight into the cellular response and gene expression of rMDSCs grown on nanostructured substrates.

Preparation and High Photocurrent Generation Enhancement of Self-Assembled Layered Double Hydroxide-Based Composite Dye Films

Understanding photocurrent conversion of layered double hydroxide (LDH) materials will be a key step in the future application of these materials to light-capturing molecular devices. In the present study, ultrathin nickel-iron layered double hydroxide/dye (NF-LDH/dye) Langmuir-Blodgett (LB) semiconductor films were prepared using an LB device and deposited on an indium tin oxide (ITO) substrate as a photoanode. The photoelectric conversion efficiency of the prepared LB semiconductor film materials was tested. A comparative experiment was performed to effectively explore the photoelectric conversion performances of the LB semiconductor film materials. Specifically, the NF-LDH cast film electrode, the dye cast film electrode, and an ultrathin composite LB film electrode were used as typical samples to explore photoelectric conversion performances. The electrochemical workstation was used to study the photocurrent density, linear scanning voltammetry curve, and electrochemical impedance spectroscopy of LB film electrodes with different layers. The results show that the film electrode cast by LDH alone or dye alone produces weak photocurrent. The photoelectric conversion efficiency of the LB film electrode is enhanced due to the different dyes' molecular structures and/or aggregations on the surface of LDH with various morphological patterns. The combined NF-LDH/dye composite LB film photoelectrode can generate a photocurrent that is 2-5 times stronger than the raw material, and the stable use efficiency is more than 92%. Present obtained composite LB films demonstrated a uniform morphology and good photoelectric conversion ability. This work provides a useful reference for the field of LDH semiconductor optoelectronic devices and solar cells.