Impact of Packing Geometry on Excimer Characteristics and Mobility in Perylene Bisimide Polycrystalline Films.

Efficient exciton transport is essential for high-performance optoelectronics. Considerable efforts have been focused on improving the exciton mobility in organic materials. While it is feasible to improve mobility in organic systems by forming well-ordered stacks, the formation of trap states, particularly the lower-lying states referred to as excimers, remains a significant challenge to enhancing mobility. The mobility of excimer excitons intricately depends on the strength of excitonic coupling in terms of Förster-type diffusive exciton transfer processes. Given that the formation and mobility of excimer excitons are highly sensitive to molecular arrangements (packing geometries), conducting comprehensive investigations into the structure-property relationship in organic systems is crucial. In this study, we prepared three types of polycrystalline films of perylene bisimide (PBI) by varying substituents at the imide and bay positions, which allowed us to tailor the properties of excimer excitons and their mobility based on packing geometries and excitonic coupling strengths. By utilizing femtosecond transient absorption spectroscopy, we observed ultrafast excimer formation in the higher coupling regime, while in the lower coupling regime, the transition from Frenkel to excimer excitons occurs with a time constant of 500 fs. Under high pump-fluence, exciton-exciton annihilation processes occur, indicating the diffusion of excimer excitons. Intriguingly, employing a three-dimensional diffusion model, we derived a diffusion constant that is 3000 times greater in the high coupling regime than in the low coupling regime. To investigate the optoelectronic properties in the form of a bulk system, we fabricated n-type organic field effect transistors and obtained 8000 times higher mobility in the high coupling regime. Furthermore, photocurrent measurements enable us to investigate the charge carrier transport by mobile excimer excitons, suggesting a 230-fold improvement in external quantum efficiency with tightly packing PBI molecules compared to the low coupling regime. These findings not only offer valuable insights into optimizing organic materials for optoelectronic devices but also unveil the intriguing potential of exciton migration within excimers.

V-Shaped Tröger Oligothiophenes Boost Triplet Formation by CT Mediation and Symmetry Breaking.

A new family of molecules obtained by coupling Tröger's base unit with dicyanovinylene-terminated oligothiophenes of different lengths has been synthesized and characterized by steady-state stationary and transient time-resolved spectroscopies. Quantum chemical calculations allow us to interpret and recognize the properties of the stationary excited states as well as the time-dependent mechanisms of singlet-to-triplet coupling. The presence of the diazocine unit in Tröger's base derivatives is key to efficiently producing singlet-to-triplet intersystem crossing mediated by the role of the nitrogen atoms and of the almost orthogonal disposition of the two thiophene arms. Spin-orbit coupling-mediated interstate intersystem crossing (ISC) is activated by a symmetry-breaking process in the first singlet excited state with partial charge transfer character. This mechanism is a characteristic of these molecular triads since the independent dicyanovinylene-oligothiophene branches do not display appreciable ISC. These results show how Tröger's base coupling of organic chromophores can be used to improve the ISC efficiency and tune their photophysics.

π-Extended Hexapyrrolylbenzenes: Exploring Charge-Transfer Phenomena in Donor-Acceptor Propellers.

A family of propeller-shaped donor-acceptor hexapyrrolylbenzenes (HPBs) were designed and synthesized by sequential nucleophilic substitution of hexafluorobenzene with π-extended pyrroles. In particular, four hybrids were obtained, containing various combinations of electron-rich and electron-poor acenaphthylene-fused pyrroles. Additionally, to probe the efficiency of ortho transfer interactions, a system was designed containing unique donor and acceptor subunits spatially separated with four unfunctionalized pyrroles. DFT calculations showed propeller-shaped geometries of all HPB molecules and separation of frontier molecular orbitals between donor and acceptor subunits. Steady-state and time-resolved photophysical measurements revealed charge-transfer (CT) character of the emission with strong positive dependence on solvent polarity. The principal CT pathway involves ortho-positioned pairs of donors and acceptors and requires bending of the acceptor in the excited state.

Aromatic-bridged and meso-meso-linked BF2-smaragdyrin dimers exhibit fast decays in polar solvents by symmetry-breaking charge transfer.

Symmetry-breaking charge transfer is one of the key process in photosynthetic reaction centers and specific artificial optoelectronic devices such as dye-sensitized solar cells. Here we report the synthesis of aromatic-bridged BF2-smaragdyrin dimers, meso-free BF2-smaragdyrin, and its meso-meso-linked BF2-smaragdyrin dimer. The decays of S1-states of these dimers are accelerated with an increase in solvent polarity and a decrease in the distance between the two BF2-smaragdyrin units, suggesting symmetry-breaking charge transfer. The fluorescence lifetimes of the dimers become shortened in polar solvents. However, ultrafast transient absorption spectroscopy do not detect charge-separated ion pairs. On the basis of these results, we conclude that the decays of the excited states of the BF2-smaragdyrin dimers are accelerated by solvation-induced symmetry-breaking charge transfer, depending on the degree of the electronic interaction between the smaragdryin units as a rare case for porphyrinoids. The degree of charge transfer is larger for dimers with larger electronic interactions.

5-Thiaporphyrinium cation: effect of sulphur incorporation on excited state dynamics.

We synthesised thionium-ion embedded aromatic porphyrinoids: a free-base 5-thiaporphyrinium cation and its zinc complex. The sulphur atom effectively participates in the macrocyclic π-conjugation. Fluorescence quantum yields of thiaporphyrinium cations were lower than 1% unlike oxaporphyrinium cations. Detailed photophysical analysis and DFT calculations clarified the vibrational mode regarding the out-of-plane motion of the sulphur atom induced ultrafast quenching of the excited state in comparison to the corresponding oxaporphyrinium cations.

Pyrene-Bridged Expanded Carbaporphyrin Nanobelts.

Two belt-like expanded carbaporphyrins (NB1 and NB2) were prepared via a one-pot procedure that involves a [6 + 3] condensation between a pyrene-bearing tetrapyrrole precursor (2) and pentafluorobenzaldehyde, followed by oxidation. Single crystal X-ray diffraction analyses revealed that NB1 and NB2 both contain six dipyrromethene moieties and three bridging pyrene units. In the structure of NB1, there are two vertically orientated pyrene units and one transverse orientated pyrene unit; however, in NB2 all three pyrene units are vertically orientated. The structural differences between NB1 and NB2 are reflected in their respective physical properties as revealed by proton NMR, UV-vis, and fluorescence spectroscopies. In contrast to all-carbon nanobelts, NB1 and NB2 contain multiple pyrrolic nitrogen donors that could serve as potential metal coordination sites. As a test of this possibility, NB2 was used to prepare an unprecedented Zn complex containing 7 Zn2+ metal centers connected by a network of bridging atoms, as confirmed by a single crystal X-ray diffraction analysis. To the best of our knowledge, this is the first example of a belt-like molecular system that can coordinate multiple metal ions both along the backbone and within its central cavity.

In Vivo Evaluation of Gamma-Irradiated and Heparin-Immobilized Small-Diameter Polycaprolactone Vascular Grafts with VEGF in Aged Rats.

The effectiveness of small-diameter vascular grafts depends on their antithrombogenic properties and ability to undergo accelerated endothelialization. The extreme hydrophobic nature of poly(ε-caprolactone) (PCL) hinders vascular tissue integration, limiting its use in medical implants. To enhance the antithrombogenicity of PCL as a biomaterial, we grafted 2-aminoethyl methacrylate (AEMA) hydrochloride onto the PCL surface using gamma irradiation; developed a biodegradable heparin-immobilized PCL nanofibrous scaffold using gamma irradiation and N-(3-dimethylaminopropyl)-N'-ethyl carbodiimide hydrochloride/N-hydroxysuccinimide reaction chemistry; and incorporated vascular endothelial growth factor (VEGF) into the scaffold to promote vascular endothelial cell proliferation and prevent thrombosis on the vascular grafts. We assessed the physicochemical properties of PCL, heparin-AEMA-PCL (H-PCL), and VEGF-loaded heparin-AEMA-PCL (VH-PCL) vascular grafts using scanning electron microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, toluidine blue O staining, and fibrinogen adsorption and surface wettability measurement. In addition, we implanted the vascular grafts into 24-month-old Sprague Dawley rats and evaluated them for 3 months. The H-PCL and VH-PCL vascular grafts improved the recovery of blood vessel function by promoting the proliferation of endothelial cells and preventing thrombosis in clinical and histological evaluation, indicating their potential to serve as functional vascular grafts in vascular tissue engineering.

Tuning the aromatic backbone twist in dipyrrolonaphthyridinediones.

This communication describes the photophysical behavior of three analogs of cyclophane bearing the dipyrrolonaphthyridinedione (DPND) core. In these molecules, intersystem crossing (ISC) can be successfully induced by distinct changes in the deviation from planarity within the DPND core, allowing at the same time the emission maximum to shift from the green to red region of the visible spectrum without any synthetic modifications of the chromophore structure. This finding may build the foundation for a new paradigm for inducing ISC-type transitions within other centrosymmetric and planar cross-conjugated chromophores.

Naphthalimide-Fused Dipyrrins: Tunable Halochromic Switches and Photothermal NIR-II Dyes.

A family of tunable halochromic switches is developed using a naphthalimide-fused dipyrrin as the core π-conjugated motif. Electronic properties of these dipyrrins are tuned by substitution of their alpha and meso positions with aryl groups of variable donor-acceptor strength. The first protonation results in a conformational change that enhances electronic coupling between the dipyrrin chromophore and the meso substituent, leading to halochromic effects that occasionally exceed 200 nm and switch the absorption between the near-infrared (NIR)-I and NIR-II ranges. A NIR-II photothermal effect, switchable by acid-base chemistry is demonstrated for selected dipyrrins. Further protonation is possible for derivatives bearing additional amino groups, leading to up to four halochromic switching step. The most electron-rich dipyrrins are also susceptible to chemical oxidation, yielding NIR-absorbing radical cations and closed-shell dications.

Enhanced Immunomodulation, Anti-Apoptosis, and Improved Tear Dynamics of (PEG)-BHD1028, a Novel Adiponectin Receptor Agonist Peptide, for Treating Dry Eye Disease.

Dry eye disease (DED) is characterized by impaired tear dynamics, leading to complex pathophysiological conditions. (PEG)-BHD1028, a peptide agonist to AdipoRs, was evaluated as a potential therapeutic agent for DED based on the reported physiological function of adiponectin, including anti-inflammation and epithelial protection. Therapeutic effects of (PEG)-BHD1028 were evaluated in experimentally induced EDE with 0.001%, 0.01%, and 0.1% (PEG)-BHD1028 in mice and 0.1%, 0.2%, and 0.4% in rabbits for 10 days. In the rabbit study, 0.05% cyclosporine was also tested as a comparator. The results from the mouse study revealed significant improvement in tear volumes, tear breakup time (TBUT), inflammation, and corneal severity score (CSS) within 10 days at all (PEG)-BHD1028 concentrations. In the rabbit study, the tear volume and TBUT significantly increased in (PEG)-BHD1028 groups compared with vehicle and 0.05% cyclosporine groups. The CSS, apoptosis rate, and corneal thickness of all (PEG)-BHD1028 and 0.05% cyclosporine groups were significantly improved relative to the vehicle group. The immune cell counts of 0.2% and 0.4% (PEG)-BHD1028 treated groups were significantly lower than those of the vehicle group. These results represent the potential of (PEG)-BHD1028 as an effective therapeutic agent for DED.

Therapeutic Efficacy of Artificial Skin Produced by 3D Bioprinting.

The skin protects the body from external barriers. Certain limitations exist in the development of technologies to rapidly prepare skin substitutes that are therapeutically effective in surgeries involving extensive burns and skin transplantation. Herein, we fabricated a structure similar to the skin layer by using skin-derived decellularized extracellular matrix (dECM) with bioink, keratinocytes, and fibroblasts using 3D-printing technology. The therapeutic effects of the produced skin were analyzed using a chimney model that mimicked the human wound-healing process. The 3D-printed skin substitutes exhibited rapid re-epithelialization and superior tissue regeneration effects compared to the control group. These results are expected to aid the development of technologies that can provide customized skin-replacement tissues produced easily and quickly via 3D-printing technology to patients.

Multiple Porous Synthetic Bone Graft Comprising EngineeredMicro-Channel for Drug Carrier and Bone Regeneration.

Due to high demand but limited supply, there has been an increase in the need to replace autologous bone grafts with alternatives that fulfill osteogenic requirements. In this study, two different types of bone grafts were tested for their drug carrying abilities along with their osteogenic properties. Two different types of alendronate-loaded bone grafts, Bio-Oss (bovine bone graft) and InRoad (biphasic synthetic bone graft) were observed to see how different concentrations of alendronate would affect the sustained release to enhance osteogenesis. In this study, defected ovariectomize-induced osteoporotic rat calvarias were observed for 28 days with three different concentrations of alendronate (0 mg, 1 mg, 5 mg) for both Bio-Oss and InRoad. A higher concentration (5 mg) allowed for a more controlled and sustained release throughout the 28-day comparison to those of lower concentrations (0 mg, 1 mg). When comparing Bio-Oss and InRoad through histology and Micro-CT, InRoad showed higher enhancement in osteogenesis. Through this study, it was observed that alendronate not only brings out robust osteogenesis with InRoad bone grafts, but also enhances bone regeneration in an alendronate-concentration-dependent manner. The combination of higher concentration of alendronate and multiple porous bone graft containing internal micro-channel structure of InRoad resulted in higher osteogenesis with a sustained release of alendronate.

Effects of Gamma Radiation-Induced Crosslinking of Collagen Type I Coated Dental Titanium Implants on Osseointegration and Bone Regeneration.

This study aimed to compare two methods of crosslinking collagen type I on implanted titanium surfaces, that is, using glutaraldehyde (GA) or gamma-rays (GRs), in a beagle dog model. For in vivo experiments, implants were allocated to three groups and applied to mandibular bone defects in beagle dogs; Group SLA; non-treated Sandblasted, large grit, acid-etched (SLA) implants, Group GA; SLA implants coated with GA crosslinked collagen type I, Group GR; SLA surface implants coated with collagen type I and crosslinked using 25 kGy of 60Co gamma radiation. New bone µCT volumes were obtained, and histologic and histometric analyses were performed in regions of interest. The GR group had significantly better new bone areas (NBAs) and bone to implant contact (BIC) results than the SLA group (p < 0.05), but the GA and GR groups were similar in this respect. New bone volumes and inter-thread bone densities (ITBD) were non-significantly different in the three groups (p > 0.05). Within the limits of this study, gamma-ray collagen crosslinking on titanium implants can be considered a substitute for glutaraldehyde crosslinking.

Charge-Delocalized State and Coherent Vibrational Dynamics in Rigid PBI H-Aggregates.

Herein, the ultrafast photoinduced dynamics and vibrational coherences for two perylenebisimide (PBI) H-aggregates showcase the formation of the excimer state and the delocalized radical anion state in the excited state, respectively. Using femtosecond transient absorption (fs-TA) and time-resolved impulsive stimulated Raman scattering (TR-ISRS) measurements, we unveiled excited-state dynamics of PBI H-aggregates in two aspects: (1) the intermolecular interactions between PBI units in H-aggregates induce the formation of new excited states, excimer and delocalized radical anion states, and (2) the intermolecular out-of-plane along the aggregate axis and the PBI core C═C stretch Raman modes can be a crucial indicator to understand the coherent exciton dynamics in H-aggregates. Notably, those excited-state Raman modes showed stationary peak positions during the excited-state dynamics. TR-ISRS analysis provides insights into the excited-state vibrational coherences concerning the formation of the excimer and charge-delocalized state in each aggregate system.

Modeling Electron-Transfer Degradation of Organic Light-Emitting Devices.

The operational lifetime of organic light-emitting devices (OLEDs) is governed primarily by the intrinsic degradation of the materials. Therefore, a chemical model capable of predicting the operational stability is highly important. Here, a degradation model for OLEDs that exhibit thermally activated delayed fluorescence (TADF) is constructed and validated. The degradation model involves Langevin recombination of charge carriers on hosts, followed by the generation of a polaron pair through reductive electron transfer from a dopant to a host exciton as the initiation steps. The polarons undergo spontaneous decomposition, which competes with ultrafast recovery of the intact materials through charge recombination. Electrical and spectroscopic investigations provide information about the kinetics of each step in the operation and degradation of the devices, thereby enabling the building of mass balances for the key species in the emitting layers. Numerical solutions enable predictions of temporal decreases of the dopant concentration in various TADF emitting layers. The simulation results are in good agreement with experimental operational stabilities. This research disentangles the chemical processes in intrinsic electron-transfer degradation, and provides a useful foundation for improving the longevity of OLEDs.

An Electron-Accepting aza-BODIPY-Based Donor-Acceptor-Donor Architecture for Bright NIR Emission.

A bright near-infrared (NIR) fluorescent molecule was developed based on the donor-acceptor-donor (D-A-D) approach using an aza-BODIPY analog called pyrrolopyrrole aza-BODIPY (PPAB) as an electron-accepting chromophore. Directly introducing electron-donating triphenylamine (TPA) to develop a D-A-D structure caused redshifts of absorption and emission of PPAB into the NIR region with an enhanced fluorescence brightness of up to 5.2×104  m-1 cm-1 , whereas inserting a phenylene linker between the TPA donor and the PPAB acceptor induced solvatochromic behavior in emission. Transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge-transfer state in the former case and the contribution of the dark charge-separated state to the excited state in the latter case. The bright D-A-D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7 % and a low amplified spontaneous emission threshold of ca. 80 µJ cm-2 , indicating the high potential for NIR optoelectronic applications.

A Light-Harvesting/Charge-Separation Model with Energy Gradient Made of Assemblies of meta-Pyridyl Zinc Porphyrins.

Self-assembly of porphyrins is a fascinating topic, not only for mimicking chlorophyll assemblies in photosynthetic organisms, but also for the potential of creating molecular-level devices. Herein, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct 1 H NMR spectrum in CDCl3 , which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the 1 H NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin-ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs.

Dual Emission of a Free-Base 5-Oxaporphyrinium Cation from its cis- and trans-NH Tautomers.

Replacement of the meso methine carbon atoms of porphyrins with heteroatoms is a powerful strategy for tuning their optical and electronic properties. In particular, 5-oxaporphyrin is an attractive target due to its importance as an intermediate in heme catabolism. In this work, we describe the synthesis and properties of a free-base 5-oxaporphyrinium cation, which was prepared by the ring-closure of a bilindione with trifluoromethanesulfonic anhydride. This free-base 5-oxaporphyrinium cation exhibits dual fluorescence originating from its unique NH tautomerism. In contrast to normal porphyrins, the cis form of the 5-oxaporphyrinium cation is more stable than the trans form due to the effective delocalization of its positive charge. We thus demonstrate here that meso-modified heteroporphyrins enable the manipulation of NH tautomerism in porphyrinic macrocycles.

Different types of agricultural land use drive distinct soil bacterial communities.

Biogeographic patterns in soil bacterial communities and their responses to environmental variables are well established, yet little is known about how different types of agricultural land use affect bacterial communities at large spatial scales. We report the variation in bacterial community structures in greenhouse, orchard, paddy, and upland soils collected from 853 sites across the Republic of Korea using 16S rRNA gene pyrosequencing analysis. Bacterial diversities and community structures were significantly differentiated by agricultural land-use types. Paddy soils, which are intentionally flooded for several months during rice cultivation, had the highest bacterial richness and diversity, with low community variation. Soil chemical properties were dependent on agricultural management practices and correlated with variation in bacterial communities in different types of agricultural land use, while the effects of spatial components were little. Firmicutes, Chloroflexi, and Acidobacteria were enriched in greenhouse, paddy, and orchard soils, respectively. Members of these bacterial phyla are indicator taxa that are relatively abundant in specific agricultural land-use types. A relatively large number of taxa were associated with the microbial network of paddy soils with multiple modules, while the microbial network of orchard and upland soils had fewer taxa with close mutual interactions. These results suggest that anthropogenic agricultural management can create soil disturbances that determine bacterial community structures, specific bacterial taxa, and their relationships with soil chemical parameters. These quantitative changes can be used as potential biological indicators for monitoring the impact of agricultural management on the soil environment.

Porphyrin-Ryleneimide Hybrids: Tuning of Visible and Near-Infrared Absorption by Chromophore Desymmetrization.

Unsymmetrically fused porphyrins containing one or two naphthalimide subunits were prepared in modular syntheses relying on electron-rich and electron-poor pyrrole building blocks. These new chromophores show progressive changes in their electron-deficient character, while retaining comparably small optical and electrochemical band gaps. The intrinsic curvature and extended optical absorption of these systems make them of interest as mono- and difunctional components of multichromophoric assemblies.