Structure-dependent thermochromism of PAZO thin films: theory and experiment

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

Chitosan functionalized poly (ε-caprolactone) nanoparticles for amphotericin B delivery

Switching resonance character within merocyanine stacks and its impact on excited-state dynamics

Characterization of pitches by ultrasonic method—I. Apparatus and preliminary results

Compared to bis(alkoxy) group para‐substituted para‐phenylene (p‐phenylene) widely used as spacer, the isomer ortho‐substituted p‐phenylene is rarely studied in constructing organic optoelectronic materials. In this manuscript, bis(hexyloxy) group ortho‐substituted p‐phenylene was used to construct hybrid thienylene‐phenylene polymer poly(EDOT‐o‐BE). The density functional theory study indicated the dihedral angles between thienylene and phenylene are 15° for ortho‐substituted EDOT‐o‐BE and 10° for para‐substituted EDOT‐p‐BE. Poly(EDOT‐o‐BE) exhibits the little potential difference between cathodic (0.61 V) and anodic (0.65 V) peaks even at the high potential scan rate, different from bis(alkoxy) para‐substituted control polymer poly(EDOT‐p‐BE). Moreover, the free‐standing poly(EDOT‐o‐BE) film displays better stability than poly(EDOT‐p‐BE) due to the little degradation of molecular chains. Compared to poly(EDOT‐p‐BE), poly(EDOT‐o‐BE) possesses higher ionic transport and different molecular aggregation. These results indicate the positions of side chains have important influence on the properties of conjugated polymer, including molecular configuration, aggregation state, film quality, electrochemical behavior and optical absorption.

In the past few years, the renormalized excitonic model (REM) approach was developed as an efficient low-scaling ab initio excited state method, which assumes the low-lying excited states of the whole system are a linear combination of various single monomer excitations and utilizes the effective Hamiltonian theory to derive their couplings. In this work, we further extend the REM calculations for the evaluations of first-order molecular properties (e.g. charge population and transition dipole moment) of delocalized ionic or excited states in molecular aggregates, through generalizing the effective Hamiltonian theory to effective operator representation. Results from the test calculations for four different kinds of one dimensional (1D) molecular aggregates (ammonia, formaldehyde, ethylene and pyrrole) indicate that our new scheme can efficiently describe not only the energies but also wavefunction properties of the low-lying delocalized electronic states in large systems.

Chalcogenide phase-change materials (PCMs) are widely applied in electronic and photonic applications, such as non-volatile memory and neuro-inspired computing. Doped Sb2Te alloys are now gaining increasing attention for on-chip photonic applications, due to their growth-driven crystallization features. However, it remains unknown whether Sb2Te also forms a metastable crystalline phase upon nanoseconds crystallization in devices, similar to the case of nucleation-driven Ge-Sb-Te alloys. Here, we carry out ab initio simulations to understand the changes in optical properties of amorphous Sb2Te upon crystallization and post annealing. During the continuous transformation process, changes in the dielectric function are highly wavelength-dependent from the visible-light range towards the telecommunication band. Our finite-difference time-domain simulations based on the ab initio input reveal key differences in device output for color display and photonic memory applications upon tellurium ordering. Our work serves as an example of how multiscale simulations of materials can guide practical photonic phase-change applications.

For almost 100 years molecular aggregates have attracted considerable scientific attention, because their electronically excited states feature interesting collective effects that result in photophysical properties that differ significantly from those of the monomeric building blocks. This concerns the delocalization of the excitation energy over many molecules in the aggregate, the redistribution of oscillator strength causing spectral shifts and changes of the fluorescence lifetimes, and changes of the spectral bandwidths of the electronic transitions. These effects result from the intermolecular interactions between the building blocks that lead to the formation of delocalized electronically excited states, commonly referred to as Frenkel excitons or molecular excitons, that can be considered as the elementary electronic excitations of molecular assemblies. Next to arousing scientific interest, these features made molecular aggregates interesting candidates for applications in the fields of sensing, light harvesting, and catalysis. Given the large body of work that addresses molecular aggregates and the information that has been accumulated in the course of time, this review attempts to provide a guide for the readers to follow the literature and to summarize the key results obtained on such systems. After recapitulating the generic photophysical properties of molecular aggregates for various geometrical arrangements, we restricted the illustrative examples to molecular aggregates that self-assemble into tubular structures. This particular choice is motivated by the fact that in nature the secondary structural elements in the most efficient photosynthetic light harvesting antenna systems feature predominantly structural motifs with cylindrical symmetry. This has boosted a wealth of research on biomimetic tubular aggregates that serve as model systems for the development of light-harvesting antenna structures for artificial photosynthesis. Since the strengths of the intermolecular interactions are imposed by the arrangement of the monomers with respect to each other, information about the morphology of the aggregates is encoded in the spectral signatures, which are in the focus of this contribution. The purpose of this review is to bring together the general results about cylindrical molecular aggregates of this large literature.

Experimental eosinophilia: VIII. Cellular responses to altered globulins within cutaneous tissue

Photopolymerization of 4-vinylbenzoate and m- and p-phenylenediacrylates in hydrotalcite interlayers

Non-conjugated luminescent materials (NCLMs) have attracted much attention in the fields of bioimaging, optoelectronic devices and sensing technologies due to their unique photophysical properties, excellent biocompatibility and environmental sustainability. However, NCLMs molecules usually lack conventional luminescent groups and exhibit aggregation-induced luminescence only at high concentrations or in the solid state, which is attributed to changes in molecular conformation and intermolecular stacking, resulting in luminescent phenomena such as aggregationinduced luminescence (AIE), concentration-enhanced luminescence, excitation-dependent luminescence, and generalized phosphorescence. It has been shown that electron-rich groups, aggregation of electron leaving domains and spatial conjugation (TSC)-induced molecular conformational rigidity in NCLMs play a crucial role in luminescence. The aim of this review is to systematically investigate the photoluminescence mechanisms of NCLMs and to study the relationship of these mechanisms with molecular structures, aggregation states and environmental factors, with special focus on AIE, cluster-triggered emission (CTE), and crosslink-enhanced emission (CEE). This review establishes a theoretical foundation for the rational design and development of NCLMs, offers novel insights into their luminescence mechanisms, and broadens the scope of their potential practical applications.

Understanding how molecular aggregation influences nonlinear optical properties is essential for advancing organic fluorophores in imaging, sensing, and photonic applications. However, the relationship between the molecular aggregation and the magnitude of nonlinear two-photon absorption cross-section remains underexplored. Here, we systematically investigate the aggregation-dependent two-photon absorption properties of the fluorophore TPAPhCN by tuning the degree of aggregation. We observe a steady increase in the two-photon absorption cross-section as the fluorophore evolves from the single molecular state to the highly aggregated state. It is found that two-photon absorption signal emerges at an early stage of aggregation that is not observable by one-photon excitation. This divergence between the nonlinear and linear optical responses enables the construction of a dual-mode optical signature, allowing TPAPhCN to function as a self-reporting probe for each aggregation state. This work presents a sensitive and structure-responsive platform for precise aggregation-state sensing in complex environments and opens new opportunities for applications in materials diagnostics and intelligent optical sensing systems.

Strengthened near-IR two-photon absorption induced emission of ESIPT chromophores by molecular aggregation

Molecular orientation within azopolymer thin films is important for their nonlinear optical properties and photonic applications. We have used optical second-harmonic generation (SHG) to study the molecular orientation of Layer-by-Layer (LbL) films of a cationic polyelectrolyte (poly(allylamine hydrochloride)) and an anionic polyelectrolyte containing azochromophore side groups (MA-co-DR13) on a glass substrate. The SHG measurements indicate that there is a preferential orientation of the azochromophores in the film, leading to a significant optical nonlinearity. However, both the signal strength and its anisotropy are not homogeneous throughout the sample, indicating the presence of large orientational domains. This is corroborated with Brewster angle microscopy. The average SHG signal does not increase with film thickness, in contrast to some reports in the literature, indicating an independent orientational order for successive bilayers. Analyzing the SHG signal as a function of the input and output polarizations, a few parameters of the azochromophore orientational distribution can be deduced. Fitting the SHG signal to a simple model distribution, we have concluded that the chromophores have an angular distribution with a slight in-plane anisotropy and a mean polar angle ranging from 45° to 80° with respect to substrate normal direction, with a relatively large width of about 25°. These results show that SHG is a powerful technique for a detailed investigation of the molecular orientation in azopolymer LbL films, allowing a deeper understanding of their self-assembling mechanism and nonlinear optical properties. The inhomogeneity and anisotropy of these films may have important consequences for their applications in nonlinear optical devices.

ConspectusAqueous organic assemblies, including molecular aggregates (MAs), conjugated polymer nanoparticles (PNPs), and their hybrids, have emerged as versatile soft materials for solar light harvesting, photocatalysis, and bioimaging. Such assemblies form through spontaneous self-organization processes, including hydrophobic collapse and multichromophoric packing, resulting in strong interunit coupling and morphology-dependent light-matter interactions. In aqueous environments, hydration shells and structural flexibility further modulate exciton delocalization, energy relaxation, and charge transfer. As a result, both MAs and PNPs exhibit complex excited-state landscapes, featuring bright and dark excitonic states, unconventional relaxation pathways, and long-lived collective excited states, which are distinct from those of the molecules in dilute solution or crystalline films.Advanced ultrafast spectroscopic techniques are employed to elucidate these excited-state processes, allowing us to correlate morphology, packing, and interunit interactions with exciton localization and delocalization, energy funneling, vibration-mediated relaxation, energy transfer, charge transfer, and charge separation across femtosecond to nanosecond time scales. In MAs, gradual aggregation and controlled structural modification tune exciton delocalization and relaxation, enabling the identification of several dark and bright excitonic manifolds, as well as long-lived charge-separated states in selected aqueous donor-acceptor assemblies. In PNPs, multichromophoric polymer chains confined within hydrated nanoparticles exhibit rapid energy redistribution, stochastic localization, and ultrafast energy funneling into collective excited states that are spatially and energetically distinct from those in MAs or films. These relaxation pathways can be precisely controlled by altering particle size and chromophore density. Analysis reveals the efficient energy and charge transfer processes from these unique excited states, which can be modulated through host-guest interactions and coupling to inorganic nanostructures.By comparing MAs, PNPs, and their hybrids within a unified spectroscopic framework, this Account highlights how excited-state dynamics evolve as organic chromophores transition from molecules to MAs and ultimately to nanoconfined PNPs, and how their morphology, packing geometry, intermolecular interactions, and interfacial coupling govern excited-state populations and energy flow. Advanced ultrafast spectroscopic methods enable direct correlation between nanoscale structure and excited-state dynamics, offering a design principle for aqueous organic assemblies, in which excited-state dynamics are deliberately engineered for functional photonic, optoelectronic, and light-harvesting applications.