Near-infrared two-photon absorption and excited state dynamics of a fluorescent diarylethene derivative

Near-infrared two-photon absorption and excited state dynamics of a fluorescent diarylethene (fDAE) derivative were investigated by time-resolved absorption and fluorescence spectroscopies. Prescreening with quantum chemical calculation predicted that a derivative with methylthienyl groups (mt-fDAE) in the closed-ring isomer has a two-photon absorption cross-section larger than 1000 GM, which was experimentally verified by Z-scan measurements and excitation power dependence in transient absorption. Comparison of transient absorption spectra under one-photon and simultaneous two-photon excitation conditions revealed that the closed-ring isomer of mt-fDAE populated into higher excited states deactivates following three pathways on a timescale of ca. 200 fs: (i) the cycloreversion reaction more efficient than that by the one-photon process, (ii) internal conversion into the S1 state, and (iii) relaxation into a lower state (S1' state) different from the S1 state. Time-resolved fluorescence measurements demonstrated that this S1' state is relaxed to the S1 state with the large emission probability. These findings obtained in the present work contribute to extension of the ON-OFF switching capability of fDAE to the biological window and application to super-resolution fluorescence imaging in a two-photon manner.

Photocatalytic CO2 Reduction Using an Osmium Complex as a Panchromatic Self-Photosensitized Catalyst: Utilization of Blue, Green, and Red Light

The photocatalytic reduction of carbon dioxide (CO2) represents an attractive approach for solar-energy storage and leads to the production of renewable fuels and valuable chemicals. Although some osmium (Os) photosensitizers absorb long wavelengths in the visible-light region, a self-photosensitized, mononuclear Os catalyst for red-light-driven CO2 reduction has not yet been exploited. Here, we discovered that the introduction of an Os metal to a PNNP-type tetradentate ligand resulted in the absorption of light with longer-wavelength (350-700 nm) and that can be applied to a panchromatic self-photosensitized catalyst for CO2 reduction to give mainly carbon monoxide (CO) with a total turnover number (TON) of 625 under photoirradiation (λ≥400 nm). CO2 photoreduction also proceeded under irradiation with blue (λ0=405 nm), green (λ0=525 nm), or red (λ0=630 nm) light to give CO with >90 % selectivity. The quantum efficiency using red light was determined to be 12 % for the generation of CO. A catalytic mechanism is proposed based on the detection of intermediates using various spectroscopic techniques, including transient absorption, electron paramagnetic resonance, and UV/Vis spectroscopy.

Phosphorus(V) Tetraazaporphyrin with an Intense, Broad CT Band in the Near-IR Region

In phosphorus tetraazaporphyrins (PTAPs), the Q- and charge-transfer (CT) bands appear as a result of configuration interaction between their excited states. On the basis of this concept, a PTAP with an intense, broad CT band in the near-IR region has been rationally designed and realized by introducing eight diphenylaminophenyl (dPAP) groups. The order of the CT and Q-bands in ascending energy was supported by magnetic circular dichroism (MCD) spectroscopy and theoretical calculations. An intense two-photon absorption was also found in the deep near-IR region.

Two-photon absorption properties of simple neutral Ir(III) complexes

A series of neutral Ir(2-phenylpyridine)3 derivatives substituted on the para-position of the pyridyl ligands with a π-conjugated substituent possessing different donor abilities has been prepared. Their two-photon absorption properties have been determined using the Z-scan technique. Such simple iridium(III) neutral complexes, which are easy to synthesize, show good two-photon absorption activity, with relevant TPA cross sections (the best is 750 GM), giving rise to multifunctional chromophores, since they present also high second-order NLO properties.

Enhanced near infrared-to-visible upconversion in the CaTiO3:Yb3+/Er3+ phosphor via the host lattice modification using co-doping of Mg2+ ions

The CaTiO3:Er3+/Yb3+ upconversion phosphor was synthesized using a simplified co-precipitation method and the effect of Mg2+ ion co-doping was investigated on the structural and optical properties focusing on the near-infrared (NIR)-to-visible upconversion. The introduction of Mg2+ ions into the host lattice produced substantial changes in the crystal structure, grain size, and absorption, thus leading to the enhancement in upconversion emission intensities. X-ray diffraction (XRD) analysis indicated the formation of polycrystalline CaTiO3-Ca4Ti3O10 composite crystals and an increase in the crystallite size was observed upon increasing the Mg2+ ion concentration in the samples. Elemental analysis by energy dispersive spectroscopy (EDS) suggested the substitution of Ca2+ ions by Mg2+ ions in the CaTiO3 host lattice. Moreover, a change in the Yb3+/Er3+ ratio from 0.25 to 1.1 indicated the redistribution of the Er3+ or Yb3+ ions caused by the Mg2+ ions. These lattice deformations further resulted in an improved absorption of Er3+ ions, exhibiting a ∼3-fold enhancement in the upconversion emission intensity (at the excitation intensity of ∼1 W cm-2).

Intramolecular Singlet Fission in Pentacene Oligomers via an Intermediate State

Intramolecular singlet fission (iSF) is an efficient strategy of multiexciton generation via a singlet exciton splitting into a correlated triplet pair in one organic molecule with more than two chromophores. Propeller-shaped iptycene-linked triisopropylsilyl(TIPS)-ethynyl functionalized pentacene oligomers (pent-monomer, pent-dimer, and pent-trimer) were synthesized, and the iSF dynamics of pent-dimer and -trimer were monitored by a visible-near-IR transient absorption (TA) spectroscopy. Quantum yields of the triplet pair, ∼80%, of both estimated by near-IR TA spectral analysis are in good agreement with the results of global analysis and triplet sensitization experiments. The iSF rate of pent-trimer is slightly faster than that of pent-dimer even with one more chromophore site. The unexpectedly weak difference indicates the existence of an intermediate process to realize iSF. The intermediate process might be determined by through-bond electronic coupling of the homoconjugation bridge in the pentacene oligomers. Our results suggest the importance of the rigid bridge to the fast iSF rate and the elongated lifetime of the correlated triplet pair in pentacene oligomers.

Unveiling a new aspect of oxocarbons: open-shell character of 4- and 5-membered oxocarbon derivatives showing near-infrared absorption

Oxocarbon derivatives consisting of 4- and 5-membered rings, referred to as croconaine and squaraine dyes and regarded as closed-shell molecules, are found to have an intermediate open-shell character from the experimental results of ¹H-NMR, ESR spectroscopy, SQUID magnetometric analysis, and X-ray crystallography. We employed two chalcogenopyrylium moieties with O and S chalcogen atoms as substitutions on oxocarbons. The singlet-triplet energy gaps (ΔE _S-T) associated with the degree of diradical nature are smaller for croconaines than for squaraines and smaller for thiopyrylium than for pyrylium groups. The diradical nature impacts the electronic transition energy that decreased with a decreasing degree of diradical contribution. They exhibit substantial two-photon absorption in the region over 1000 nm. The diradical character y of the dye was determined experimentally from the observed one- and two-photon absorption peaks and the triplet energy level. The present finding provides new insight into diradicaloids with the contribution of non-Kekulé oxocarbon and also showcases the correlation between the electronic transition energy and their diradical character.

Oxidative Cyclodehydrogenation of Trinaphthylamine: Selective Formation of a Nitrogen-Centered Polycyclic π-System Comprising 5- and 7-Membered Rings

We describe a new type of nitrogen-centered polycyclic scaffold comprising a unique combination of 5-, 6-, and 7-membered rings. The compound is accessible through an intramolecular oxidative cyclodehydrogenation of tri(1-naphthyl)amine. To the best of our knowledge this is the very first example of a direct 3-fold cyclization of a triarylamine under oxidative conditions. The unusual ring fusion motif is confirmed by X-ray crystallography and the impact of cyclization on the electronic and photophysical properties is investigated both experimentally and theoretically based on density-functional theory (DFT) calculations. The formation of the unexpected product is rationalized by detailed mechanistic studies on the DFT level. The results suggest the cyclization to occur under kinetic control via a dicationic mechanism.

Importance of steric bulkiness of iridium photocatalysts with PNNP tetradentate ligands for CO2 reduction

A series of Ir complexes has been developed as multifunctional photocatalysts for CO₂ reduction to give HCO₂H selectively. The catalytic activities and photophysical properties vary widely across the series, and the bulky group insertion resulted in the formation of HCO₂H and CO with the catalyst turnover number of >10 400.

Triplet-triplet annihilation photon upconversion from diphenylhexatriene and ring-substituted derivatives in solution

We report that diphenylhexatriene (DPH) and its ring-substituted derivatives act as emitter molecules in triplet-triplet annihilation photon upconversion (TTA-UC). A palladium porphyrin derivative, meso-tetraphenyl-tetrabenzoporphine palladium complex (PdTPBP), which acts as a sensitiser in TTA-UC, and DPH derivatives were dissolved in tetrahydrofuran (THF). The solution showed blue-green to green UC emission under photoexcitation at 640 nm in a nitrogen atmosphere. The UC quantum efficiency (η_UC) values of the DPHs were estimated, with (E,E,E)-1,6-bis[4-(di-2-picolylamino)phenyl]hexa-1,3,5-triene (pico DPH) showing the highest. In addition, the quantum yields of triplet energy transfer (TET) and triplet-triplet annihilation (TTA), which are elementary processes in TTA-UC, were estimated, as well as the triplet lifetimes of each DPH derivative. The results indicate that the TTA process governs the value of η_UC.

From 2,5-Diformyl-1,4-dihydropyrrolo[3,2-b]pyrroles to Quadrupolar, Centrosymmetric Two-Photon-Absorbing A-D-A Dyes

An original approach has been developed for the insertion of formyl substituents at positions 2 and 5 of 1,4-dihydropyrrolo[3,2-b]pyrroles by conversion of thiazol-2-yl substituents. The synthetic utility of these formyl groups was investigated, and a series of centrosymmetric A−π–D−π–A frameworks were constructed. The two-photon absorption of the quadrupolar pyrrolo[3,2-b]pyrrole possessing two dicyanovinylidene flanking groups is attributed to an S₀ → (S₁) → S₄ transition which has a large TPA cross-section (1300 GM) for a molecule of this size.

X ray spectroscopy on 𝚵− atoms (J-PARC E03, E07 and future)

X-ray spectroscopy of hadronic atoms is a powerful method to study strong interaction between hadrons and nuclei. At J-PARC, we have conducted two experiments, J-PARC E07 and E03, for hadronic atoms with a doubly strange hyperon, Ξ−, aiming at the world-first detection of their X-rays. The first measurement is performed as a byproduct of J-PARC E07 experiment with the hybrid emulsion technique. The second one, J-PARC E03, is a dedicated experiment for detection of Ξ− Fe atom X rays. The preliminary results and the present status of E07 and E03 are shown in this article. Future prospects of Ξ−-atomic X-ray spectroscopy are also discussed. A new measurement has been proposed for detecting Ξ− C atom X rays, where a novel Ξ− tracking method will be applied to realize an improved signal to noise ratio.

Preparation status of missing-mass spectroscopy for 𝚵 hypernuclei with S-2S magnetic spectrometer

J-PARC E70 experiment measures the missing-mass of Ξ hypernuclei (12ΞBe) in Hadron Experimental Facility at J-PARC. We aim to reach the best missing-mass resolution of 2 MeV/c2 in FWHM with a new magnetic spectrometer S-2S. The high-resolution spectroscopy of Ξ hypernuclei will play an important role to understand the unknown ΞN interaction. The experiment will start at the beginning of 2023. This article presents the preparation status.

A Highly Durable, Self-Photosensitized Mononuclear Ruthenium Catalyst for CO2 Reduction

A novel mononuclear ruthenium (Ru) complex bearing a PNNP-type tetradentate ligand is introduced here as a self-photosensitized catalyst for the reduction of carbon dioxide (CO2). When the pre-activation of the Ru complex by reaction with a base was carried out, an induction period of catalyst almost disappeared and the catalyst turnover numbers (TONs) over a reaction time of 144 h reached 307 and 489 for carbon monoxide (CO) and for formic acid (HCO2H), respectively. The complex has a long lifespan as a dual photosensitizer and reduction catalyst, due to the sterically bulky and structurally robust (PNNP)Ru framework. Isotope-labeling experiments under 13CO2 atmosphere indicate that CO and HCO2H were both produced from CO2.

Kinetics of photon upconversion by triplet-triplet annihilation: a comprehensive tutorial

This perspective article provides a comprehensive but organized tutorial introduction of the kinetics related to photon upconversion (UC) by triplet-triplet annihilation (TTA) (TTA-UC). The field of TTA-UC is multi-disciplinary and rapidly growing with the involvement of researchers from diverse backgrounds. TTA-UC consists of a series of tangled photophysical processes, so a solid understanding of the kinetic features and consequences is important to develop and evaluate materials for TTA-UC. This tutorial starts with an introduction of the standard model of TTA-UC along with the assumptions used in the model. The essential concept of the spin statistics for TTA and how this concept is related to the singlet branching ratio, which directly affects the efficiency of UC, are then explained through step-by-step analyses. Using these foundations, solutions for the steady-state behaviors are derived, featuring the universal curve that describes the excitation intensity dependence of the UC quantum yield for any sample type. Various useful functions for analyzing experimental data are also introduced and summarized. The transient behaviors of TTA-UC are then discussed along with their equations, and the usefulness for analyzing transient experimental data is explained using examples. In this article, self-consistent derivations and relevant references are provided for an easy understanding of the advanced discussion and analyses.

Quadrupolar Dyes Based on Highly Polarized Coumarins

The fluorescence and other photophysical parameters of highly polarized, quadrupolar bis-coumarins possessing an electron-rich pyrrolo[3,2-b]pyrrole bridging unit are highly dependent on the linking position between both chromophores. Delocalization of the LUMO on the entire π-system results in intense emission and strong two-photon absorption.

Molecular crystalline capsules that release their contents by light

Here, we present single crystalline capsules of a photoresponsive molecule produced by simple recrystallization from organic solutions without direct human processing. During the crystal growth process, a movie was taken of the capsule taking in the organic solution. The capsules responded rapidly (<1 s) to the UV light stimuli and released the captured solution or solute. In principle, they can take in any substance dissolved in organic solvents, and their size can be controlled. Moreover, the capsule can be broken by multi-photon excitation using a near-infrared laser within the biological window. Furthermore, because the molecular packing in the crystal is unidirectional, the response can be controlled by the polarization of the light. This study shows the new potential of photoresponsive molecules.

Evaluation of anatomical references for locating the course of the posterior superior alveolar artery for dental implant surgery

This retrospective cohort study aimed to identify the best anatomical reference for predicting the posterior superior alveolar artery (PSAA) location. Computed tomographic images of 90 maxillary sinuses were evaluated. We studied five references, including the alveolar crest, maxillary sinus floor, zygomatoalveolar crest, hard palate and soft palate, and measured the distances between them and the PSAA. Variations in the distance were evaluated by the standard deviation and coefficient of variation (CV). The zygomatoalveolar crest was an unstable reference, owing to its high standard deviation and CV. The smallest CV was for the distance between the alveolar crest and PSAA, although the distance was smaller in edentulous jaws than dentulous jaws. The distance between the sinus floor and PSAA was larger in male and edentulous patients. The PSAA was detected in 40.0%, 44.4%, 54.4% and 56.7% of the sinus walls at the first and second premolar and the first and second molar positions, respectively. At these tooth positions, the respective heights above the hard palate were 11.2 ± 4.9, 8.2 ± 4.9, 6.2 ± 2.8 and 8.1 ± 2.9 mm. The hard palate was the most stable reference for predicting the location of the PSAA, irrespective of sex, age and dentition.

Anion-Responsive Molecules That Exhibit Switching of Two-Photon Optical Properties

Two-photon-excited fluorescent probes are important for two-photon microscopy for biomedical studies. In contrast to the many examples of probes for cationic species, such as metal ions, there have been fewer reports on the control of two-photon optical properties by anions because in such systems it is difficult to control the associated π-electronic states. This Minireview summarizes anion-responsive molecules that exhibit changes in two-photon optical properties and describes their molecular design and anion-response mechanisms, which are driven by changes in covalent bonds and noncovalent interactions. Results from a recent study of two-photon systems, where geometries and optical properties are modulated by anion binding, are also discussed.

THU0099 THE TIME REQUIRED TO ESCALATE THE DOSAGE OF METHOTREXATE TO THERAPEAUTIC LEVELS AFFECTS THE TREATMENT SUCCESS ACHIEVED DURING PHASE I OF THE TREATMENT ALGORITHM FOR RHEUMATOID ARTHRITIS RECOMMENDED BY THE EUROPEAN LEAGUE AGAINST RHEUMATISM

Background:

In the treatment of rheumatoid arthritis (RA), methotrexate (MTX) monotherapy is undoubtedly the most cost-effective therapy available. However, no clear evidence exists for the adopted method of MTX usage, except for guidelines that have been formulated using empirical knowledge.

Objectives:

We aimed to retrospectively evaluate the treatment method used to administer MTX in order to identify factors influencing the success rate of MTX treatment in phase I of the European League Against Rheumatism (EULAR) recommendation in the treatment algorithm of RA.

Methods:

A total of 520 RA patients were considered for inclusion in this study, of whom 183 were eligible as they had been treated with MTX monotherapy from 2013 to 2018. The exclusion criteria included the following: unknown MTX prescription details (200 cases), deviation from the treatment algorithm i.e. use of a combination of conventional synthetic disease-modifying antirheumatic drugs (csDMARDs) before MTX therapy (4 cases), and a long duration of MTX escalation that deviated from the treat-to-target concept (133 cases).

Patients who received csDMARD monotherapy (including switching between csDMARDs) prior to MTX monotherapy were not excluded.

The primary outcome was failed MTX monotherapy with transition to phase II.

The escalation time to the required maximum therapeutic dose of MTX and the lower limit of the required maintenance therapeutic dose that resulted in successful MTX monotherapy was determined using the receiver operating characteristic (ROC) curve. Accordingly, previous results obtained from ROC curve analyses were categorized into two groups for regression analysis: patients who tolerated MTX monotherapy and those who failed MTX monotherapy.

We performed a regression analysis on the background factors observed during their first visit to our department and two previously identified factors. The background factors included prognostically unfavourable factors related to joint destruction despite RA treatment (i.e. rheumatoid factor [RF] levels, anti-citrullinated peptide antibody [ACPA] levels, acute phase reactant levels, swollen joint counts, joint damage, and disease activity).

Results:

The background factors that were statistically different were age at onset, RF levels, ACPA levels, current dose and continuity of MTX therapy, glucocorticoid (GC) use, and time until first DMARD use. After this analysis, we determined to exclude GC use from subsequent analyses as it was found to be statistically different between age groups.

Using the ROC analysis, we found that the escalation time to the maximum dose of MTX was 2.07 weeks. Further, logistic regression analysis was used to analyse each of the previously reported statistically significant factors. Statistical differences were observed in the age at onset and the escalation time of initial MTX induction therapy.

We also performed a backward stepwise logistic regression analysis on the previous two factors and conventional risk factors related to joint destruction with RA treatment. Statistical difference was observed in the escalation time of initial MTX induction therapy.

Furthermore, propensity score matching was performed by analysing the previously mentioned influencing factors and prognostically unfavourable factors of joint destruction using a backward stepwise logistic regression analysis. We identified statistical difference in the escalation time of MTX induction therapy (odds ratio: 1.957 [95% confidential interval: 1.036-3.697], p=.039).

Conclusion:

These results suggest that rapid escalation to the required MTX therapeutic dose, within 2.07 weeks, during initial RA treatment can shorten the time required to achieve the treatment target. By doing this, RA patients on MTX therapy in phase I may achieve a greater treatment responsive. Thus, the short escalation time is an important factor influencing successful MTX monotherapy in the RA treatment algorithm.

Disclosure of Interests:

None declared

Switching of Two-Photon Optical Properties by Anion Binding of Pyrrole-Based Boron Diketonates through Conformation Change

Two-photon absorption (TPA) dyes with intense fluorescence can be used to detect small chemical species and as sensors and bioimaging probes for specific analytes. Various TPA dyes responding to a number of external stimuli have been reported. Among them, biologically important anionic species have not been used as agents to control TPA properties because their direct electronic influences on the transition dipole moments of dyes are typically small. In this study, dipyrrolyldiketone BF₂ complexes substituted with π-extended units exhibited efficient TPA properties that could be regulated by conformation changes induced by anion binding. The TPA intensity decreased to 1/5 of the original intensity upon anion binding, which was much larger than that observed for one-photon absorption. Anion detection was achieved by a change in the emission intensity of spatially resolved spots of two-photon-excited fluorescence (TPEF) in the sample. Experimental and theoretical studies were performed to understand the mechanism of the TPA property control and showed that the drastic changes in the transition dipole moments upon conformation changes between the straight and bending forms of the π-electronic systems caused the TPA and TPEF intensities drop.

Chalcone-based molecules: Experimental and theoretical studies on the two-photon absorption and molecular first hyperpolarizability

Five chalcone-based molecules denominated by C-3 ((E)-1-(4-methoxyphenyl)-3-phenylprop-2-en-1-one), C-4 ((E)-1,3-bis(4-methoxyphenyl)prop-2-en-1-one), C-5 ((E)-1-(benzo[d][1,3]dioxol-5-yl)-3-(4-methoxyphenyl)prop-2-en-1-one), C-6 ((E)-3-(naphthalen-1-yl)-1-phenylprop-2-en-1-one) and C-7 ((E)-1-(4-methoxyphenyl)-3-(naphthalen-1-yl)prop-2-en-1-one) were synthesized by Claisen-Schmidt reaction in solution of NaOH in water/ethanol 2:1. The aldehydes used were benzaldehyde, anisaldehyde, and β-naphthaldehyde, while the used ketones were acetophenone, p-methoxyacetophenone, and 3,4-methylenedioxyacetophenone. Z-scan and hyper-Rayleigh scattering techniques were used to study the nonlinear optical properties of these compounds in dichloromethane medium. By using Z-scan technique with femtosecond pulses, two-photon absorption cross-sections (σ^TPA) were determined, while the first molecular electronic hyperpolarizabilities (β^HRS) were evaluated by the hyper-Rayleigh scattering technique, with picosecond pulses. From the recorded two-photon absorption spectra, it was identified that compound C-7 presented the highest σ^TPA, regarding the HOMO-LUMO transition, with a value of 40 GM, while C-6 achieved the lowest value for the same transition with 13 GM. Concerning the values of the first molecular hyperpolarizability, compound C-4 presented the highest value, 38 × 10^-30 cm⁴ statvolt^-1, while C-3 presented the lowest β^HRS value of about 16 × 10^-30 cm⁴ statvolt^-1. Time-dependent density functional theory calculations were used to simulate the one- and two-photon absorption spectra, as well to predict the theoretical value of β^HRS in dichloromethane and vacuum medium.

Triplet-triplet annihilation upconversion through triplet energy transfer at a nanoporous solid-liquid interface

We report the triplet-triplet annihilation (TTA) upconversion (UC) through triplet energy transfer (TET) from a sensitiser fixed on a solid surface to free emitters dissolved in solution. A carboxylic-acid derivative of Pt-porphyrin was used as the sensitiser fixed on an amino-treated surface of continuous nanoporous glass without aggregation. UC emission was observed under photoexcitation of 532 nm for porphyrin-fixed glass immersed in an emitter solution of 9,10-diphenylanthracene (DPA), showing that TET occurs through the solid-liquid interface. The dynamics of TET was analysed through both phosphorescence decay of the sensitiser and UC emission rise from the emitter. Two TET components with different rate constants were found, slower than diffusion-controlled reactions in solution by 1-2 orders of magnitude. Nevertheless, the solid surface TET rates were fast enough to obtain a high quantum yield over the solid-liquid interface. By melting DPA and soaking it into sensitiser-fixed porous glass, we fabricated an all-solid system enabling TTA-UC through the bulk interface.

Solid-State, Near-Infrared to Visible Photon Upconversion via Triplet-Triplet Annihilation of a Binary System Fabricated by Solution Casting

Herein, triplet-triplet annihilation upconversion (TTA-UC) from near-infrared (NIR, 785 nm) to visible (yellow, centered at 570 nm) regions has been demonstrated in the binary solid of condensed chromophores. Microparticles of the binary solid comprising rubrene as a matrix (emitter) and π-extended Pd-porphyrin as a dopant (sensitizer) in a mole ratio of 1000:1 were obtained by solution casting. Excitation intensity dependence and quantum yield (QY) of the upconverted emission were characterized for individual particles under a microscope and revealed a low threshold intensity (∼100 mW/cm²) as compared to the solution and moderate UC-QY (∼0.5%) in the NIR range. The factors contributing to the UC-QY were investigated by time-resolved and steady-state spectroscopies. It was found that the intersystem crossing of the sensitizer, triplet energy transfer, and TTA occurred efficiently in the binary solid, and the fluorescence QY of the emitter governed the UC-QY.

First molecular electronic hyperpolarizability of series of π-conjugated oxazole dyes in solution: an experimental and theoretical study

In this work, we report for the first time, the experimental and theoretical first molecular electronic hyperpolarizability of eleven π-conjugated oxazoles compounds in toluene medium, by using the hyper-Rayleigh scattering (HRS) technique.

Perylenetetracarboxy-3,4:9,10-diimide derivatives with large two-photon absorption activity

Perylenetetracarboxy-3,4:9,10-diimides with large TPA cross-sections.

Synergetic Effects of Triplet-Triplet Annihilation and Directional Triplet Exciton Migration in Organic Crystals for Photon Upconversion

In condensed solids, triplet exciton migration and succeeding triplet-triplet annihilation (TTA) are major bottleneck processes for efficient photon upconversion (UC) using sunlight excitation. We theoretically investigated the reaction times of TTA and the triplet-triplet energy transfer (TTET) as the elementary processes of triplet exciton migration in organic crystals of two molecular species: 9,10-diphenylanthracene (DPA) and its double-strapped alkyl  derivative (C7-sDPA) as the models of a recently reported crystalline system of TTA-UC by Kamada et al. The reaction times calculated based on Marcus theory clarified that the dimensionality of TTET and synergetic effects of TTA and TTET are responsible for the high UC quantum yield as well as their triplet lifetimes.

Near infrared two-photon-excited and -emissive dyes based on a strapped excited-state intramolecular proton-transfer (ESIPT) scaffold

Strapped acceptor–π–donor–π–acceptor type fluorophores exhibit intense near infrared emission, together with near infrared two-photon absorption.

Fluorophores that can undergo excited-state intramolecular proton transfer (ESIPT) represent promising scaffolds for the design of compounds that show red-shifted fluorescence. Herein, we disclose new near infrared-emissive materials based on a dialkylamine-strapped 2,5-dithienylpyrrole as an ESIPT scaffold. The introduction of electron-accepting units to the terminal positions of this scaffold generates acceptor–π–donor–π–acceptor (A–π–D–π–A) type π-conjugated compounds. Following the ESIPT, the electron-donating ability of the core scaffold increases, which results in a substantially red-shifted emission in the NIR region, while increasing the oscillator strength. The electron-accepting units play a vital role to achieve intense and red-shifted emission from the ESIPT state. The strapped dialkylamine chain that forms an intramolecular hydrogen bond is also essential to induce the ESIPT. Moreover, an extended A–π–D–π–A skeleton enables two-photon excitation with the NIR light. One of the derivatives that satisfy these features, i.e., borylethenyl-substituted 5, exhibited an intense NIR emission in polar solvents such as acetone (λ_em = 708 nm, Φ_F = 0.55) with a strong two-photon-absorption band in the NIR region.

Real-time detection and discrimination of visual perception using electrocorticographic signals

OBJECTIVE

Several neuroimaging studies have demonstrated that the ventral temporal cortex contains specialized regions that process visual stimuli. This study investigated the spatial and temporal dynamics of electrocorticographic (ECoG) responses to different types and colors of visual stimulation that were presented to four human participants, and demonstrated a real-time decoder that detects and discriminates responses to untrained natural images.

APPROACH

ECoG signals from the participants were recorded while they were shown colored and greyscale versions of seven types of visual stimuli (images of faces, objects, bodies, line drawings, digits, and kanji and hiragana characters), resulting in 14 classes for discrimination (experiment I). Additionally, a real-time system asynchronously classified ECoG responses to faces, kanji and black screens presented via a monitor (experiment II), or to natural scenes (i.e. the face of an experimenter, natural images of faces and kanji, and a mirror) (experiment III). Outcome measures in all experiments included the discrimination performance across types based on broadband γ activity.

MAIN RESULTS

Experiment I demonstrated an offline classification accuracy of 72.9% when discriminating among the seven types (without color separation). Further discrimination of grey versus colored images reached an accuracy of 67.1%. Discriminating all colors and types (14 classes) yielded an accuracy of 52.1%. In experiment II and III, the real-time decoder correctly detected 73.7% responses to face, kanji and black computer stimuli and 74.8% responses to presented natural scenes.

SIGNIFICANCE

Seven different types and their color information (either grey or color) could be detected and discriminated using broadband γ activity. Discrimination performance maximized for combined spatial-temporal information. The discrimination of stimulus color information provided the first ECoG-based evidence for color-related population-level cortical broadband γ responses in humans. Stimulus categories can be detected by their ECoG responses in real time within 500 ms with respect to stimulus onset.

Enhanced phosphorescence properties of a Pt-porphyrin derivative fixed on the surface of nano-porous glass

Room-temperature phosphorescence of a Pt-porphyrin derivative was enhanced in quantum yield and lifetime by fixing it on the surface of nanometer-scale pores of porous glass.

Efficient Cycloreversion Reaction of a Diarylethene Derivative in Higher Excited States Attained by Off-Resonant Simultaneous Two-Photon Absorption

Off-resonant excitation of the closed-ring isomer of a photochromic diarylethene derivative at 730 nm induced the efficient cycloreversion reaction with a yield of ∼20%, while the reaction yield was only 2% under one-photon excitation at 365 nm. Excitation wavelength dependence of the one-photon cycloreversion reaction yield under steady-state irradiation in a wide wavelength range showed that the specific electronic state leading to the large cycloreversion reaction yield, which is originally forbidden in the optical transition but partially allowed owing to the low symmetry of the molecule, is spectrally overlapped with the electronic state accessible by the allowed one-photon optical transition in the UV region. Femtosecond transient absorption spectroscopy also revealed that the off-resonant two-photon excitation preferentially pumped the molecule into the specific state, leading to the 10-fold enhancement of the cycloreversion reaction.

Passive functional mapping guides electrical cortical stimulation for efficient determination of eloquent cortex in epilepsy patients

Electrical cortical stimulation (ECS) is often used in presurgical evaluation procedures for patients suffering from pharmacoresistant epilepsy. Real-time functional mapping (RTFM) is an alternative brain mapping methodology that can accompany traditional functional mapping approaches like ECS. In this paper, we present a combined RTFM/ECS system that aims to exploit the common ground and the advantages of the two procedures for improved time/effort effectiveness, patients' experience and safety. Using the RTFM and ECS data from four patients who suffer epilepsy, we demonstrate that the RTFM-guided ECS procedure hypothetically reduces the number of electrical stimulations necessary for eloquent cortex detection by 40%.