J-type Aggregates Research Articles

Two-Dimensional Supramolecular Polymorphism in Cyanine H- and J-Aggregates.

We designed a new cyanine dye 1, with two pedant rod-like groups, capable of forming two distinct two-dimensional (2D) supramolecular polymorphs in methylcyclohexane; an H-type aggregate (Agg-H2) and a J-type aggregate (Agg-J). Importantly, these two polymorphs were not accessed through polymerization events, and instead through the thermal transformation of a third particle-like polymorph (Agg-H1) formed by the anti-cooperative assembly of 1. While Agg-H2 is generated upon cooling the solution of Agg-H1 by a thermoreversible polymorph transition, the Agg-J was obtained through a hidden pathway by combining sonication and cooling to the Agg-H1 solution. This is the first report on the obtention of H- and J-type cyanine polymorphs that in turn could be isolated in solid-state to render two new 2D photoactive materials. This paper unveils new strategies for designing 2D supramolecular polymers using calamitic residues, but also undercovers relevant aspects of pathway complexity and polymorph transitions that might be crucial for developing novel photonic systems.

A Donor-Acceptor Molecular Octopus and the CLICK Procedure in Columnar Liquid Crystal Phases.

Two star-shaped mesogens with a (meso-tetraphenylporphinato) zinc (II) core and bithiophene conjugated arms with 3,4,5-trisdodecyloxyphenyl periphery were synthesized. One of these molecules was decorated with four fullerenes via an aliphatic spacer. This is the sterically overcrowded compound with an octapodal morphology. The other star lacks the fullerenes and provides free space between the conjugated arms. This mesogen does not aggregate in solution, but in solid state it forms a hexagonal columnar and a highly ordered oblique helical columnar phase, while the octopus molecule assembles in an amorphous solid. Photophysical studies of the octapodal compound in solution and the solid thin film reveal the formation of J-type aggregates, in which the interaction between donors (porphyrin) and acceptors (fullerene) dominates leading to absorption bands in the NIR region of the spectra. The mixture of both compounds results in a self-assembly which is called the Click procedure. Fullerenes of the octopus nanosegregate in the pockets of the star mesogens generating hexagonal columnar structures with a regular stacking along the columnar axis. Thus providing free space is a tool to control the competition between supramolecular interactions and nanosegregation. Such liquid-crystalline donor-acceptor structures may play a role in future LC photovoltaic applications.

NIR laser-activated phthalocyanine loaded lipid nanoparticles targeting M2 macrophage for improved photoacoustic imaging-guided photothermal therapy

The development of novel phototheranostic agents with significant potential in bioimaging-guided therapy is highly desirable for precise tumor therapy. Herein, NIR laser-activated ruthenium phthalocyanine (PcRu) loaded sub-30 nm targeting lipid nanoparticles (α-PcRu-NPs) were fabricated for photoacoustic imaging (PAI)-guided photothermal therapy (PTT). Due to the formation of J-type aggregation of PcRu in the core of the nanostructure, the α-PcRu-NPs exhibited high stability, efficient NIR absorption, reduced singlet oxygen generation, high photothermal activity, and intense photoacoustic signal. With the M2 macrophage target peptide (M2pep) modification and small size of α-PcRu-NPs, in vivo evaluations reveal that α-PcRu-NPs can specifically target and deeply penetrate the tumor foci. Under a high contrast PAI guidance with α-PcRu-NPs (744 nm, 0.35 μW), it also realizes superior photothermal therapy (PTT) for breast cancer under 670 nm laser irradiation (0.5 W/cm2). The prominent therapeutic efficacy of α-PcRu-NP-based PTT not only directly kills tumor cells, but also enhances the immune response by promoting dendritic cell maturation and increasing cytotoxic T cell infiltration. Thus, this work broadens the applications of phthalocyanine derivatives as phototheranostics in the PAI-guided PTT field.

Distinct vibrational motions promote disparate excited-state decay pathways in cofacial perylenediimide dimers.

A complex interplay of structural, electronic, and vibrational degrees of freedom underpins the fate of molecular excited states. Organic assemblies exhibit a myriad of excited-state decay processes, such as symmetry-breaking charge separation (SB-CS), excimer (EX) formation, singlet fission, and energy transfer. Recent studies of cofacial and slip-stacked perylene-3,4:9,10-bis(dicarboximide) (PDI) multimers demonstrate that slight variations in core substituents and H- or J-type aggregation can determine whether the system follows an SB-CS pathway or an EX one. However, questions regarding the relative importance of structural properties and molecular vibrations in driving the excited-state dynamics remain. Here, we use a combination of two-dimensional electronic spectroscopy, femtosecond stimulated Raman spectroscopy, and quantum chemistry computations to compare the photophysics of two PDI dimers. The dimer with 1,7-bis(pyrrolidin-1'-yl) substituents (5PDI2) undergoes ultrafast SB-CS from a photoexcited mixed state, while the dimer with bis-1,7-(3',5'-di-t-butylphenoxy) substituents (PPDI2) rapidly forms an EX state. Examination of their quantum beating features reveals that SB-CS in 5PDI2 is driven by the collective vibronic coupling of two or more excited-state vibrations. In contrast, we observe signatures of low-frequency vibrational coherence transfer during EX formation by PPDI2, which aligns with several previous studies. We conclude that key electronic and structural differences between 5PDI2 and PPDI2 determine their markedly different photophysics.

Effect of dipolar state on J-type aggregation of acceptor group modified pyrene-based push-pull systems

The present work demonstrates the ground and excited state aggregation behavior of two pyrene-based push–pull systems (Pyr-MC and Pyr-PyA) both in solid and solution state. The UV–Vis spectra of these molecules show a unique broaden spectral pattern at lower energy region (400–600 nm) in both H2O and solid state. Further, along with the local (intense) emission band, a new (less intense) band is appeared at higher wavelength region (∼550 nm) in water, which is due to the formation of aggregates. Interestingly, it is the lowest energy emission out of all previously reported emission by pyrene derivatives. The experimental results suggest the formation of J-type aggregation in solid and solution. The average lifetime of these molecules is also measured in different solvents. Intriguingly, the ground/excited state J-type aggregation in solid and solution are similar in nature in spite of different mode of intermolecular interactions, and are supported by experimental results. The dipolar state plays an important role on the J-type aggregation process. The QTAIM (quantum theory of atom in molecule) theoretical framework is applied to analyze and understand the properties of molecules in terms of the distribution of electrons and the topological features of the electron density within a molecule. Importantly, bond paths provide information about the nature of chemical bonds, including their strength and directionality.

Influence of subphase temperature on Langmuir layers and thin films of A3B-type porphyrine derivative

The influence of aqueous subphase temperature on the formation and stability of floating layers of 5-(4-hydroxyphenyl)-10,15,20-tris(4-hexadecyloxyphenyl)porphyrin (P-OH) was investigated using the Langmuir technology. It was found that the increase in the subphase temperature from 1 to 40 °C leads to a loosening of floating layers (an increase in the area per molecule in the floating layer by ∼15% and a decrease in the surface compression modulus by more than two times). The stability of floating layers (i.e., the ability of a floating layer to maintain its area under the action of a constant compressive force) decreases with increasing subphase temperature. It has been shown that the most stable floating layers are formed at subphase temperatures lower than 30 °C. Monolayer films on solid substrates were obtained using the Langmuir-Schafer technique at subphase temperatures of 1, 10, 20, 30, and 40 °C. The surface relief of these films was studied by atomic force microscopy (AFM). The AFM analysis revealed that the films transferred from the aqueous subphase at a temperature of 20 °C had the highest continuity and the lowest roughness. The absorption spectra of the floating layers were obtained, in which a bathochromic shift of the Soret band and Q-bands were registered (by 19 nm at 20 °C) in comparison with chloroform solution spectrum. This shift is a consequence of the strong intermolecular π–π* interaction, resulting in the formation of J-type aggregates. The Soret band in the spectra of the floating layers shifted from 436 to 441 nm with an increase in subphase temperature from 1 to 40 °C. In the absorption spectra of thin films (8 transfers), the indicated shifts of absorption bands as well as a broadening of the Soret band are preserved. The results of this work can be used in the targeted creation of film samples with specific structure and properties.

Pyrobacteriopheophorbide-a derivatives possessing various hydrophilic esterifying groups at the C17-propionate residues for photodynamic therapy.

Aiming at the application to photodynamic therapy, natural bacteriochlorophyll-a was converted to chemically stable free-base derivatives possessing different kinds of hydrophilic C17-propionate residues. These semi-synthetic bacteriochlorins were found to have self-assembling ability in an aqueous environment and formed stable J-type aggregates in a cell culture medium containing 0.2% DMSO. The electronic absorption spectra of all the sensitizers showed Qy absorption maxima at 754 nm in DMSO as their monomeric states, while a drastic shift of the red-most bands to ca. 880 nm was observed in the aqueous medium. The circular dichroism spectra in the medium showed much intense signals compared to those measured in DMSO, supporting the formation of well-ordered supramolecular structures. By introducing hydrophilic side chains, the bacteriochlorin sensitizers could be dispersed in the aqueous medium as their J-aggregates without the use of any surfactants. Cellular uptake efficiencies as well as photodynamic activities were evaluated using human cervical adenocarcinoma HeLa cells. Among the 11 photosensitizers investigated, the best result was obtained for a charged derivative possessing trimethylammonium terminal (17-CH2CH2COOCH2CH2N+(CH3)3I-) and photocytotoxicity of EC50 = 0.09 μM was achieved by far-red light illumination of 35 J/cm2 from an LED panel (730 nm).

Polymer-Chain Aggregation-induced Electrical Gating at the H- and J-aggregate P3HT

This research explores how aggregation influences the electrical behavior at both the planar - heterojunction poly(3-hexylthiophene) (P3HT)/SiO2 and P3HT/ZnO nanocrystal (NC) interfaces. The formation of H- and J-type aggregates leads to distinct molecular ordering and packing structures, manifesting as changes in threshold voltage shifts (electrical gating) as well as absorption and luminescence properties. Ultrasound irradiation (sonication) significantly alters the molecular arrangement in P3HT, favoring the formation of H-aggregates over the typically formed J-aggregates. In pristine P3HT, J-aggregates facilitate efficient exciton movement and electrical generation, resulting in higher photocurrents compared to sonicated-P3HT, which predominantly forms H-aggregates. Field-effect transistors (FETs) based on sonicated P3HT exhibit a more positive threshold voltage and increased mobility, indicating the presence of more mobile charge carriers, even in the absence of an applied voltage. In interfaces with ZnO NC, pristine P3HT demonstrates a considerable shift in threshold voltage under illumination, attributed to electron trapping. Conversely, sonicated P3HT interfaced with ZnO NC shows less electron trapping and minimal change in threshold voltage. This study underscores how the type of aggregate (H or J) in P3HT significantly dictates light-induced electrical gating. Ultrasound irradiation (sonication), while enhancing mobility by improving crystallinity, leads to a decrease in photocurrent efficiency in H-aggregates compared to the J-aggregates present in pristine-P3HT.

Boosting Excited-State Energy Transfer by Anchoring Dipole Orientation in Binary Thermally Activated Delayed Fluorescence/J-Aggregate Assemblies.

Förster resonance energy transfer (FRET) has been widely applied in fluorescence imaging, sensing and so on, while developing useful strategy of boosting FRET efficiency becomes a key issue that limits the application. Except optimizing spectral properties, promoting orientation factor (κ2) has been well discussed but rarely utilized for boosting FRET. Herein, we constructed binary nano-assembling of two thermally activated delayed fluorescence (TADF) emitters (2CzPN and DMAC-DPS) with J-type aggregate of cyanine dye (C8S4) as doping films by taking advantage of their electrostatic interactions. Time-resolved spectroscopic measurements indicated that 2CzPN/Cy-J films exhibit an order of magnitude higher kFRET than DMAC-DPS/Cy-J films. Further quantitative analysing on kFRET and kDET indicated higher orientation factor (κ2) in 2CzPN/Cy-J films play a key role for achieving fast kFRET, which was subsequently confirmed by anisotropic measurements. Corresponding DFT/TDDFT calculation revealed strong "two-point" electrostatic anchoring in 2CzPN/Cy-J films that is responsible for highly orientated transitions. We provide a new strategy for boosting FRET in nano-assemblies, which might be inspired for designing FRET-based devices of sensing, imaging and information encryption.

Induced Chirality in Canthaxanthin Aggregates Reveals Multiple Levels of Supramolecular Organization.

Carotenoids tend to form supramolecular aggregates via non-covalent interactions where the chirality of individual molecules is amplified to the macroscopic level. We show that this can also be achieved for non-chiral carotenoid monomers interacting with polysaccharides. The chirality induction in canthaxanthin (CAX), caused by heparin (HP) and hyaluronic acid (HA), was monitored by chiroptical spectroscopy. Electronic circular dichroism (ECD) and Raman optical activity (ROA) spectra indicated the presence of multiple carotenoid formations, such as H- and J-type aggregates. This is consistent with molecular dynamics (MD) and density functional theory (DFT) simulations of the supramolecular structures and their spectroscopic response.

Solvent Geometry Regulated J- and H-Type Aggregates of Photoswitchable Organogelator: Phase-Selective Thixotropic Gelation and Oil Spill Recovery.

We demonstrate supramolecular polymerization and formation of 1D nanofiber of azobenzene based organogelator (AZO-4) in cyclic hydrocarbon solvents (toluene and methylcyclohexane). The AZO-4 exhibits J- and H-type aggregates in toluene: MCH (9 : 1) and MCH: toluene (9 : 1) respectively. The type of aggregate was governed by the geometry of the solvents used in the self-assembly process. The J-type aggregates with high thermal stability in toluene is due to the enhanced interaction of AZO-4 π- surface with the toluene π-surface, whereas H-aggregate with moderate thermal stability in MCH was due to the interruption of the cyclic hydrocarbon in van der Waals interactions of peripheral chains of AZO-4 molecule. The light induced reversible photoisomerization is observed for both J- and H-aggregates. The macroscopic property revealed spontaneous and strong gelation in toluene preferably due to the strong interactions of the AZO-4 nanofibers with the toluene solvent molecules compared to the MCH. The rheological measurements revealed thixotropic nature of the gels by step-strain experiments at room temperature. The thermodynamic parameter (ΔHm) of gel-to-sol transition was determined for all the gels to get more insight into the gelation property. Furthermore, the phase selective gelation property was extended to the oil spill recovery application using diesel/water and petrol/water mixture.

Synthesis of cyanated Naphthalene diimide−Hydroazaacenes: Amphoteric-redox, low-lying LUMO, bright-red emission, aggregation and aromaticity evaluation

Herein we explored the synthesis and functionalization of NDI-hydroazaacenes, via two routes, at both the peripheries along the long-axis of the molecules. For the first time, we successfully performed cyanation reactions at the hydroazaacenes without the use of Pd-catalyst, enabling straightforward access to symmetric and asymmetrically substituted molecules. We also accessed NDI-hydroazaacenes with shorter substituents at the axial-positions allowing us to realize the single crystal data, which interestingly revealed π-stacked dimers with slipped orientation with the axial groups self-sorted in a syn-syn and anti-anti fashion. The tetracyano-substituted NDI-hydroazaacene showed a DFT predicted LUMO of −4.34 eV, which makes it the most electron-deficient hydroazaacene reported till date. In addition, we explored the amphoteric-redox properties of the NDI-hydroazaacene by generating radical anion/dianion and radical cation states. The molecules showed interesting J-type aggregation with concomitant color change from pink to blue in solution. Further, the molecules exhibited bright-red emission with quantum yields of 29–72 %. Computational studies showed the aromaticity/antiaromaticity can be subtly modulated by the substituents (H/Br/CN) on the rings.

Electronically and geometrically complementary perylenediimides for kinetically controlled supramolecular copolymers.

The synthesis of 3,4,9,10-benzo[d,e]isoquinolino[1,8-g,h]quinoline-tetracarboxylic diimide (BQQDI) 1 endowed with peripheral trialkoxybenzamide fragments is reported and its self-assembling features investigated. The peripheral benzamide moieties generate metastable monomeric species that afford a kinetically controlled supramolecular polymerization. The electron-withdrawing character of 1 in comparison with previously reported PDIs 2, together with the similar geometry, makes this dye an optimal candidate to perform seeded supramolecular copolymerization yielding four different supramolecular block copolymers. Whilst heteropolymers poly-1-co-2a, poly-2a-co-1 and poly-1-co-2b present an H-type arrangement of the monomeric units, heteropolymer poly-2b-co-1, prepared by seeding the chiral, metastable monomers of 2b with achiral seeds of 1, produces chiral, J-type aggregates. Interestingly, the monosignated CD signal of pristine poly-2b changes to a bisignated CD signal most probably due to the formation of columnar domains around the seeds of 1 which implies the blocky nature of the supramolecular copolymers formed.

Pathway complexity in aqueous J-aggregation of an ionic BODIPY amphiphile

An ionic BODIPY amphiphile exhibited kinetic-controlled and thermodynamic-controlled aggregation pathways in water, which led to the formation of two J-type aggregates with distinct spectroscopic properties and morphologies.

Narcissistic self-sorting in Zn(II) porphyrin derived semiconducting nanostructures.

The narcissistic self-sorted phenomenon is explicitly attributed to the structural similarities in organic molecules. Although such relevant materials are rarely explored, self-sorted structures from macrocyclic π-conjugated-based p- and n-type organic semiconductors facilitate the increase of exciton dissociation and charge separation in bulk heterojunction solar cells. Herein, we report two extended π-conjugated derivatives consisting of zinc-porphyrin-linked benzothiadiazole acting as an acceptor (PB) and anthracene as a donor (PA). Despite having the same porphyrin π-conjugated core in PA and PB, variations in donor and acceptor moieties make the molecular packing form one-dimensional (1D) self-assembled nanofibers via H- and J-type aggregates. Interestingly, a dissimilar aggregate of PA and PB exists as a mixture (PA + PB), promoting narcissistic self-sorted structures. Electrochemical impedance investigation reveals that the electronic characteristics of self-sorting assemblies are influenced by the difference in electrostatic potentials for PA and PB, resulting in a transitional electrical conductivity of 0.14 S cm-1. Therefore, the design of such materials for the fabrication of effective photovoltaics is promoted by these extraordinary self-sorted behaviors in comparable organic π-conjugated molecules.

Structure and isomerization behavior relationships of new push-pull azo-pyrrole photoswitches.

A family of stilbenyl-azopyrroles compounds 2a-d and 3a-d was efficiently obtained via a Mizoroki-Heck C-C-type coupling reaction between 2-(4'-iodophenyl-azo)-N-methyl pyrrole (1a) and different vinyl precursors. The influence of the π-conjugated backbone and the effect of the pyrrole moiety were correlated with their optical properties. Studies via UV-Visible spectrophotometry revealed that the inclusion of EWG or EDG favors a red-shift of the main absorption band in these azo compounds compared with their non-substituted analogues. Furthermore, there is a clear influence between the half-life of the Z isomer formed by irradiation with white light and the push-pull behavior of the molecules. In several cases, the stilbenyl-azopyrroles led to the formation of J-type aggregates in binary MeOH : H2O solvents, which are of interest for water compatible applications.

Low band gap semiconducting covalent organic framework films with enhanced photocatalytic hydrogen evolution

A contrasting photocatalytic mechanism was observed for semiconducting covalent organic frameworks (COFs). J-type aggregation favors exciton migration in the powder state, while charge transport governs the photocatalytic activity in the films.

Effect of aggregation configuration of molecular fluorophore CZA on photoluminescence properties of carbon dots

The effect of aggregation configuration of molecular fluorophore citrazinic acid (CZA) on the photoluminescence (PL) properties of carbon dots (CDs) has been investigated using first-principles method. The structural stability of all aggregates has been analyzed, and the results show that the most stable structures are J-type CZA aggregates with head-to-tail configurations and the CZA/CD aggregates are bonded by replacing H atoms on the CD edges with de-OH from the pyridine ring of CZA. The luminescent properties of CZA/CD aggregates are mainly affected by the binding modes and binding sites. When the sites belong to electron-donating groups, electron-withdrawing groups or sp2 domain, the PL spectra of CDs are shifted and the luminescent intensities are significantly enhanced. The results suggest that covalently bonded CZA/CD aggregates are responsible for the high fluorescence quantum yield of CD. Moreover, the distance between the centers of the two pyridine rings in H-type CZA dimers less than 3.5 Å is prone to π-π stacking, leading to fluorescence quenching of aggregates. The present work is helpful in understanding the effect of molecular fluorophores on the PL properties of CDs and provides theoretical guidance for the controllable synthesis of CDs.

Naphthalene Diimide-Based Orange Emitting Luminogen: A Fluorometric Probe for Thiol Sensing through the Click Reaction.

Fluorometric sensors have gained considerable attention in various fields, including environmental monitoring, biomedical research, and clinical diagnostics. This article delineates the fabrication of an orange emitting naphthalene diimide (NDI) derivative consisting of maleimide moiety (NDI-mal) for fluorometric sensing of thiols. Spherical shaped organic nanoparticles (∼100-150 nm) were constructed by NDI-mal in dimethyl sulfoxide (DMSO)/dimethylformamide (DMF)-water through J-type aggregation. NDI-mal displayed self-assembly driven aggregation-induced emission (AIE) through excimer formation at λem= 588 nm at fw = 99 vol % DMSO/DMF-water. Naphthyl residue at both terminals of NDI-mal facilitates intramolecular charge transfer (ICT) from the donor naphthyl residue to the acceptor NDI core. The fluorescence intensity of NDI-mal fluorescent organic nanoparticles (FONPs) got quenched in the presence of thiols due to thiol-maleimide adduct formation (Michael addition). NDI-mal FONPs selectively probed thiol functionalized small molecules (4-aminothiophenol), biomolecules (glutathione (GSH)), and proteins (reduced BSA) with high sensitivity having a limit of detection of 15.3 nM, 6.0 nM, and 9.2 ng/mL, respectively. Importantly, thiol sensing was selective against analogous small molecules, biomolecules, and proteins devoid of thiol moieties. Cellular imaging demonstrated selective diagnosis of cancer cells by NDI-mal FONPs through quenching of its emission upon interaction with thiols in B16F10 cells due to the high abundance of GSH in cancer cells compared to NIH3T3 cells. NDI-mal FONPs emitted their native fluorescence inside cells subjected to reactive oxygen species mediated thiol oxidation via Fenton's reaction. Notably, GSH-maleimide adduct formation by NDI-mal FONPs displayed notable therapeutic efficacy against cancer cells having ∼2.4-fold higher killing of B16F10 in comparison to NIH3T3 cells possibly through oxidative stress induced apoptosis owing to the depletion in the GSH level. Thus, NDI-mal AIE-gen successfully emerged as a selective and sensitive probe toward thiols through thiol-maleimide click chemistry with therapeutic ability against cancer cells in the absence of systematic intervention.

Electron-Withdrawing Substituents Allow Boosted NIR-II Fluorescence in J-Type Aggregates for Bioimaging and Information Encryption.

Developing molecular fluorophores with enhanced fluorescence in aggregate state for the second near-infrared (NIR-II) imaging is highly desirable but remains a tremendous challenge due to the lack of reliable design guidelines. Herein, we report an aromatic substituent strategy to construct highly bright NIR-II J-aggregates. Introduction of electron-withdrawing substituents at 3,5-aryl and meso positions of classic boron dipyrromethene (BODIPY) skeleton can promote slip-stacked J-type arrangement and further boost NIR-II fluorescence of J-aggregates via increased electrostatic repulsion and intermolecular hydrogen bond interaction. Notably, NOBDP-NO2 with three nitro groups (-NO2 ) shows intense NIR-II fluorescence at 1065 nm and high absolute quantum yield of 3.21 % in solid state, which can be successfully applied in bioimaging, high-level encoding encryption, and information storage. Moreover, guided by this electron-withdrawing substituent strategy, other skeletons (thieno-fused BODIPY, aza-BODIPY, and heptamethine cyanine) modified with -NO2 are converted into J-type aggregates with enhanced NIR-II fluorescence, showing great potential to convert aggregation caused emission quenching (ACQ) dyes into brilliant J-aggregates. This study provides a universal method for construction of strong NIR-II emissive J-aggregates by rationally manipulating molecular packing and establishing relationships among molecular structures, intermolecular interactions, and fluorescence properties.