Self-organization of a sulfonamido-porphyrin in Langmuir monolayers and Langmuir-Blodgett films

Porous crystalline materials for memories and neuromorphic computing systems

Porous crystalline materials usually include metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs) and zeolites, which exhibit exceptional porosity and structural/composition designability, promoting the increasing attention in memory and neuromorphic computing systems in the last decade. From both the perspective of materials and devices, it is crucial to provide a comprehensive and timely summary of the applications of porous crystalline materials in memory and neuromorphic computing systems to guide future research endeavors. Moreover, the utilization of porous crystalline materials in electronics necessitates a shift from powder synthesis to high-quality film preparation to ensure high device performance. This review highlights the strategies for preparing porous crystalline materials films and discusses their advancements in memory and neuromorphic electronics. It also provides a detailed comparative analysis and presents the existing challenges and future research directions, which can attract the experts from various fields (e.g., materials scientists, chemists, and engineers) with the aim of promoting the applications of porous crystalline materials in memory and neuromorphic computing systems.

Oriented Growth of Thin Films of Covalent Organic Frameworks with Large Single-Crystalline Domains on the Water Surface

It has been a longstanding challenge to rationally synthesize thin films of organic two-dimensional (2D) crystals with large single-crystalline domains. Here, we present a general strategy for the creation of 2D crystals of covalent organic frameworks (COFs) on the water surface, assisted by a charged polymer. The morphology of the preorganized monomers underneath the charged polymer on the water surface and their diffusion were crucial for the formation of the organic 2D crystals. Thin films of 2D COFs with an average single-crystalline domain size of around 3.57 ± 2.57 μm² have been achieved, and their lattice structure, molecular structure, and grain boundaries were identified with a resolution down to 3 Å. The swing of chain segments and lattice distortion were revealed as key factors in compensating for the misorientation between adjacent grains and facilitating error corrections at the grain boundaries, giving rise to larger single-crystalline domains. The generality of the synthesis method was further proved with three additional 2D COFs. The oriented single-crystalline domains and clear grain boundaries render the films as model materials to study the dependence of the vertical conductivity of organic 2D crystals on domain sizes and chemical structures, and significant grain boundary effects were illustrated. This study presents a breakthrough in the controlled synthesis of organic 2D crystals with structural control at the molecular level. We envisage that this work will inspire further investigation into the microstructure-intrinsic property correlation of 2D COFs and boost their application in electronics.

Fluorescence Spectroscopy of Porphyrins and Phthalocyanines: Some Insights into Supramolecular Self-Assembly, Microencapsulation, and Imaging Microscopy

The molecular interactions of anionic tetrasulfonate phenyl porphyrin (TPPS) with poly(amido amine) (PAMAM) dendrimers of generation 2.0 and 4.0 (G2 and G4, respectively) forming H- or J-aggregates, as well as with human and bovine serum albumin proteins (HSA and BSA), were reviewed in the context of self-assembly molecular complementarity. The spectroscopic studies were extended to the association of aluminum phthtalocyanine (AlPCS4) detected with a PAMAM G4 dendrimer with fluorescence studies in both steady state and dynamic state, as well as due to the fluorescence quenching associated to electron-transfer with a distribution of lifetimes. The functionalization of TPPS with peripheral substituents enables the assignment of spontaneous pH-induced aggregates with different and well-defined morphologies. Other work reported in the literature, in particular with soft self-assembly materials, fall in the same area with particular interest for the environment. The microencapsulation of TPPS studies into polyelectrolyte capsules was developed quite recently and aroused much interest, which is well supported and complemented by the extensive data reported on the Imaging Microscopy section of the Luminescence of Porphyrins and Phthalocyanines included in the present review.

Cycloaddition of CO2 to epoxides using di-nuclear transition metal complexes as catalysts

Cycloaddition of CO₂ to epoxides was carried out selectively using di-nuclear Cu(ii), Co(ii) or Ni(ii)/n-Bu₄NI catalyst system with high turnover frequency.

Optical spectroscopy and photochemistry of porphyrins and phthalocyanines

Studies of excited singlet and triplet states of porphyrins and phthalocyanines in organized media of reverse micelles, vesicles, monolayers, and Langmuir-Blodgett films along with more complex supramolecular organizates with proteins and dendrimers, are reported. Self-assembly in these systems was followed by imaging and temporal fluorescence techniques.

Synthesis and structural characterization of a new self-assembled disulfide linked meso-tetrakis-porphyrin macromolecular array

The synthesis of a new self-assembled porphyrin macrostructure based on disulfide bonds, is presented. This constitutes a new way to directly connect porphyrins in macromolecular arrays, to complement the usual methods of intermolecular hydrogen bonds and metal coordination bonding.

Enhanced optical and nonlinear optical responses in a polyelectrolyte templated Langmuir-Blodgett film

Optical and nonlinear optical properties like fluorescence and second harmonic generation (SHG) of molecular materials can be strongly influenced by the mode of assembly of the molecules. The Langmuir-Blodgett (LB) technique is an elegant route to the controlled assembly of molecules in ultrathin films, and complexation of ionic amphiphiles in the Langmuir film by polyions introduced in the aqueous subphase provides a simple and efficient access to further control, stabilization, and optimization. The monolayer LB film of the hemicyanine-based amphiphile, N-n-octadecyl-4-[2-(4-(N,N-ethyloctadecylamino)phenyl)ethenyl]pyridinium possessing a "tail-head-tail" structure, shows fluorescence as well as SHG response. The concomitant enhancement of both of these linear and nonlinear optical attributes is achieved through templating with the polyanion of carboxymethylcellulose. Brewster angle and atomic force microscopy reveal the influence of polyelectrolyte templating on the morphology of the Langmuir and LB films. Polarized absorption and fluorescence spectroscopy provide insight into the impact of complexation with the polyelectrolyte on the orientation and deaggregation of the hemicyanine headgroup leading to fluorescence and SHG enhancement in the LB film.

Interfacial assemblies of atypical amphiphilic porphyrins: hydrophobicity/hydrophilicity of substituents, annealing effects, and supramolecular chirality

Interfacial molecular assemblies of eight atypical amphiphilic porphyrins, substituted with hydrophobic or hydrophilic substituents but without long alkyl chains on their molecular skeletons, have been investigated in terms of supramolecular chiralty generation and amplification. It is found that all of the originally organized interfacial molecular assemblies display very weak or undetectable supramolecular chirality. Interestingly, for those porphyrins bearing hydrophilic substituents, it is found that their molecular assemblies display distinct supramolecular chirality when applying a thermal annealing treatment. In contrast, for those bearing hydrophobic substituents, the formed assemblies remain achiral after similar treatment. This investigation suggests that the hydrophobicity/hydrophilicity of the substituents of the atypical amphiphilies could affect the occurrence of the interfacial mirror symmetry breaking substantially. It discloses that, although some of the interfacial assemblies are superficially achiral, a thermal annealing treatment could endow them with evident supramolecular chirality.

Fluorescence enhancement in Langmuir-Blodgett films: role of amphiphile structure, orientation, and assembly

Suppression of self-quenching of fluorescence emission in supramolecular systems is of fundamental interest in the design and development of novel optical materials. While a number of molecular design and assembly strategies have been formulated for the fabrication of molecular crystals with enhanced light emission, parallel explorations based on systematic approaches in the domain of molecular ultrathin films are rare. We have investigated Langmuir-Blodgett films of amphiphilic molecules bearing the same hemicyanine choromophore headgroup but with different possibilities of attachment of the octadecyl hydrocarbon chain, under different deposition conditions. Fluorescence spectroscopy studies indicate enhanced light emission in the derivative with a "tail-head-tail" structure. The observed trends are attributed to the amphiphile structure, nature of deposition, and the chromophore orientations revealed through polarized absorption spectra of the films. The study suggests a simple design strategy toward realization of molecular ultrathin films with enhanced light emission.

Acidification and assembly of porphyrin at an interface: counterion matching, selectivity, and supramolecular chirality

The interfacial diprotonation and assemblies of a free-base achiral porphyrin, 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)-21H,23H-porphine, on various acidic subphases were investigated. It has been shown that the compound could be diprotonated in situ on an acidic subphase and can form assemblies. The interfacially organized supramolecular assemblies were transferred onto a solid substrate, and the assemblies showed supramolecular chirality. Interestingly, the supramolecular chirality of the assemblies of the diprotonated species showed a counterion-dependent behavior. For the assemblies fabricated from the aqueous HCl subphases, a strong Cotton effect (CE) could be observed, although the porphyrin itself is achiral. When an aqueous HBr solution was used as the subphase, the assemblies showed a weak CE, whereas no CE could be detected for the assemblies formulated from the HNO3 or HI subphase. Interestingly, when a mixture of HBr and NaCl, or HNO3 and NaCl, was employed as the subphase, the formed assemblies displayed chiral features similar to those fabricated on the HCl subphase, suggesting that the Cl(-) could be preferentially visualized in terms of supramolecular chirality, although the system itself is composed of achiral species. On the basis of the experimental facts and a theoretical calculation, an explanation with regard to the different sizes of the counterions and the distinct binding affinities of the counteranions to the diprotonated porphyrin species has been proposed. Our findings provide new insights into the assembly of the diprotonated porphyrins as well as the interfacially occurring symmetry breaking.

Fluorescence lifetime imaging study of a thin protein layer on solid surfaces

Understanding the fundamental interactions between proteins and solid surfaces is essential in the area of implantable medical devices. Fluorescence methods offer the sensitivity required to study the formation of the initial thin protein layers that mediate biocompatibility of materials. Thin protein layers (bovine serum albumin labelled with 1-anilino-8-naphthalenesulfonate, BSA-ANS) deposited on several surfaces (glass, silicon, stainless steel, polystyrene, and silver island film) were studied using confocal frequency domain Fluorescence Lifetime Imaging Microscopy (FLIM) and single-point multifrequency lifetime analysis techniques. FLIM provides spatial information about both fluorophores located on the surface and physicochemical parameters of the surface microenvironment. The average fluorescence lifetimes (tau(av)) of the adsorbed BSA-ANS generated by the contact between a protein solution and the material surface were measured by the multifrequency modulation and phase shift. Results indicate that tau(av) values of the albumin complexes on the surfaces (approximately 12 ns) are, in general, shorter than tau(av) found in the bulk solution (approximately 14 ns). For some surfaces, like polystyrene and silver island film the differences in tau(av) of the adsorbed BSA-ANS were found to be much greater. The differences in fluorescence lifetimes may indicate structural changes in the BSA protein induced by contact with the surface.

Imaging proteins in vivo using fluorescence lifetime microscopy

Fluorescence lifetime imaging (FLIM) represents a key optical technique for imaging proteins and protein interaction in vivo. We review the principles and recent advances in the application of the technique, instrumentation and molecular probe development.