Optical, third order non-linear optical and electrochemical properties of dipolar, centrosymmetric and C2v organoimido polyoxometalate derivatives

A family comprising seven arylimido-polyoxometalate (POM) hybrid chromophores (three of which are new), with linear dipolar,C 2vand linear centrosymmetric geometries have been synthesised and studied by electronic absorption spectroscopy, electrochemistry, Z-scans (two photon absorption, TPA) and computation (DFT/TD-DFT). These reveal that POM acceptor units are an effective basis for TPA materials: the centrosymmetric bis-POM chromophores produce significant cross sections (δup to 82 GM) from a single aryl bridge, a similar performance to larger dipolar π-systems combining carbazole or diphenylamino donors with the imido-POM acceptor. DFT/TD-DFT calculations indicate strong communication between POM and organic components is responsible for the linear and non-linear optical behaviour of these compounds, while electrochemical measurements reveal class II mixed valence behaviour resulting from an interplay of through-bond and through-space effects

Immersive Surgical Anatomy of the Frontotemporal-Orbitozygomatic Approach.

The frontotemporal-orbitozygomatic (FTOZ) approach is widely used for accessing anterolateral lesions in skull base surgery. Many studies have described the technique and quantified the surgical exposure and freedom provided by the FTOZ approach. However, few studies have provided a detailed analysis of the technique and surgical landmarks using three-dimensional (3D) models. In this study, we aimed to create a collection of volumetric models (VMs) and stereoscopic media on the step-by-step surgical technique of the FTOZ approach using cadaveric dissections. The FTOZ approach was divided into eight major steps: positioning, incision of the skin, dissection of scalp flap, mobilization of the temporalis muscle, dissection of periorbita, craniotomy, drilling of basal structures, and dural opening. The MacCarty keyhole and inferior orbital fissure are major surgical landmarks that were referenced for the six bony cuts. Photogrammetry and structured light scanning were used to construct high-resolution VMs. We illustrated the two-piece FTOZ craniotomy, followed by the one-piece and three-piece FTOZ craniotomies. Stereoscopic images, videos, and VMs were produced for each step of the surgical procedure. In addition, the mini-orbitozygomatic (MOz) and orbitopterional (OPt) approaches were considered and described as possible alternatives to the FTOZ approach. Recent advances in 3D technology can be implemented in neurosurgical practice to further enhance our spatial understanding of neurovascular structures. Surgical approaches should be carefully selected and tailored according to the patient's unique pathology and needs

Efekt protonace na dynamiku excitovaného stavu pyrimidinových chromoforů

The effect of protonation on the photophysics and especially on the excited state dynamics of two pyrimidine chromophores, bearing the A-(pi-D)(2) and A-(pi-D)(3) structure, is studied by means of fs-ps and ns time resolved fluorescence spectroscopy. Three different acids, namely camphorsulphonic (CSA), acetic (AcOH) and trifluoroacetic acid (TFA) were used. The chromophores bear the pyrimidine electron deficient heterocycle as electron-withdrawing group, used as protonation site, as well as diphenylamino electron donors. Protonation is revealed through the emergence of red-shifted absorption and fluorescence bands accompanied by a quenching of the fluorescence of the neutral molecules. Time-resolved dynamics reveal that protonation with CSA and TFA do not influence the excited state lifetime of the chromophores, pointing to a static quenching process. On the other hand, the lifetime is decreased upon protonation with AcOH. Further investigation based on the Stern-Vollmer plots showed that addition of AcOH leads to both dynamic and static quenching.Byl studován efekt protonace na fotofyziku dvou pyrimidinových chromoforů prostřednictvím fluorescenční spektroskopie. Byly využity tři kyseliny, kafrsulfonová, octová a trifluoroctová

Fotofyzikální a protonační time-resolved studie donor-akceptorového rozvětveného systému s pyridinovými akceptory

A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues, by means of ambient and low temperature steady state spectroscopy and femtosecond to nanosecond time-resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors, and acetylene pi-bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed intramolecular charge transfer state on the picosecond time scale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Forster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral toward the protonated species on the 1 ps time scale is revealed.Porovnávací studie fotofyzikálních vlastností oktupolárních pyridin-trifenylaminů s jejich kvadrupolárními a dipodálními analogy pomocí steady-state spektroskopie a femtosekundové až nanosekundové time-resolved fluorescenční spektroskopie při běžné a nízké teplotě. Látky byly studovány v rozpouštědlech s různou polaritou, byl studován také vliv přídavků kyseliny octové vedoucí k protonaci pyridinových skupin. Díky kontrolované protonaci vzorky vykazovaly širokopásovou emisi pokrývající téměř celé viditelné spektrum

Cooperative Self-Assembly Enables Two-Dimensional H-type Aggregation of a Sterically Crowded Perylene-Bisimide Dimer

Identifying the role of multiple cooperative supramolecular interactions and the working mechanism underlying the formation of sophisticated, well-defined self-assembled architectures is definitely a challenging and formidable task in understanding the complexity in chemical systems and engineering the properties of advanced materials. The topological design of multifunctional tectons, capable of self-organizing into patterned supramolecular assemblies comprising stacked aromatic molecules, is of particular importance because it can lead to the predictable emergence of controlled functions with tailored electronic properties. Herein, we provide spectroscopic, structural, and mechanistic insights on metal-ion-mediated self-assembly of a charged, amphiphilic perylene-bisimide (PBI) dimer S into two-dimensional (2D) arrays consisting of parallel columnar PBI stacks with a precise spatial arrangement and pattern behavior, using a readily accessible design strategy. The building block (S), a centrosymmetric PBI homodimer bearing a disulfonated trans-stilbene core, was designed to concurrently feature high complexation directionality with a strong binding affinity through multiple supramolecular interactions. In solvents that efficiently solvate PBI, e.g., chloroform, the zinc ion interacts strongly through electrostatic interactions with the negatively charged core of S, and with the πcloud of the stilbene moiety (cation-πinteractions) forming simple 1:1 adducts. In methanol, the findings manifest the efficient formation of well-defined aggregates with H-type excitonic coupling. A single-crystal X-ray structure reveals, despite the sterically crowded bay area of PBIs constituting S, an unprecedented pattern of 2D arrays comprising face-to-face, slipped π-stacked PBI interdimers that pack in parallel columns. This molecular arrangement explains the quenched fluorescence in solution, as well as the appearance of weak excimer-like fluorescence both in solution and crystals. The spectroscopic and structural findings converge to the conclusion that the development of aggregates in solution proceeds by a cooperative growth process driven by a collection of different supramolecular interactions, i.e., electrostatic (core of S), π-πstacking (terminal PBIs), and multiple C-H···π(bay substituents). A corresponding aggregation model fits satisfactorily the experimental data in solution and allows extracting the association constants and spectra of the equilibrated species. © Copyright © 2019 American Chemical Society

Branching effect on the linear and nonlinear optical properties of styrylpyrimidines

International audienceThis contribution aims at investigating the branching effect on the steady state, time resolved fluorescence and two-photon absorption (2PA) properties of dimethylamino and diphenylamino substituted styrylpyrimidine derivatives, by means of a combined experimental and theoretical study. In contrast to classical branched molecules with a triphenylamine central core and electron accepting groups at the periphery, here, branched molecules with reverse topology and different symmetries are examined, namely a styrylpyrimidine group is used as the electron withdrawing core and dimethylamino or diphenylamino donors are incorporated at the periphery. Besides, compared to the great majority of existing branched systems, the herein studied molecules do not have C3 symmetry. For this reason, the region of the linear and non-linear optical spectra of the two and three branched chromophores is actually similar. Interestingly, while the one-photon absorption spectra of one-branched systems versus two- or three-branched ones are spectrally shifted, there is almost no spectral shift in the main 2PA spectral region. Meanwhile, there is still an enhancement of both linear and nonlinear optical responses. Overall, here we developed a strategy that enhances the 2PA response while maintaining the spectral position. Specifically, 2PA cross section values as high as 500 GM have been obtained for the diphenylamino A–(π–D)3 molecule in dichloromethane

Triazine-Substituted Zinc Porphyrin as an Electron Transport Interfacial Material for Efficiency Enhancement and Degradation Retardation in Planar Perovskite Solar Cells

Motivated by the excellent electron-transfer capability of porphyrin molecules in natural photosynthesis, we introduce here the first application of a porphyrin compound to improve the performance of planar perovskite solar cells. The insertion of a thin layer consisting of a triazine-substituted Zn porphyrin between the TiO2 electron transport layer and the CH3NH3PbI3 perovskite film significantly augmented electron transfer toward TiO2 while also sufficiently improved the morphology of the perovskite film. The devices employing porphyrin-modified TiO2 exhibited a significant increase in the short-circuit current densities and a small increase in the fill factor. As a result, they delivered a maximum power conversion efficiency (PCE) of 16.87% (average 14.33%), which represents a 12% enhancement compared to 15.01% (average 12.53%) of the reference cell. Moreover, the porphyrin-modified cells exhibited improved hysteretic behavior and a higher stabilized power output of 14.40% compared to 10.70% of the reference devices. Importantly, nonencapsulated perovskite solar cells embedding a thin porphyrin interlayer showed an elongated lifetime retaining 86% of the initial PCE after 200 h, while the reference devices exhibited higher efficiency loss due to faster decomposition of CH3NH3PbI3 to PbI2. © 2018 American Chemical Society

Lithium Doping of ZnO for High Efficiency and Stability Fullerene and Non-fullerene Organic Solar Cells

We report on the effect of lithium doping of zinc oxide used as electron-transport layer in organic solar cells based on both fullerene and non-fullerene acceptors. The experimental and theoretical results indicate that lithium ions intercalated within the ZnO lattice as dopants replace interstitial zinc defects that act as trap states and give rise to a higher electron conductivity without significantly altering work function and valence band edge. The enhanced electron carrier extraction/collection efficiency, the suppressed bimolecular and interface trap-assisted recombination losses and the higher electron mobility of the photoactive blend synergistically contribute to the superior performance of PTB7-Th:PC71BM-based fullerene devices utilizing doped ZnO layers with an optimized lithium concentration of 5 wt %. Such devices increased their maximum PCE from 8.59% (average 8.05%) to 10.05% (average 9.53%) while, simultaneously, boosting their long-term stability. Moreover, non-fullerene solar cells based on the PTB7-Th:IT-4F blend exhibited PCEs up to 8.96% and maintained more than 80% of their initial efficiency after 1000 h storage in the dark upon using the lithium modified ZnO electron transport layer. © 2019 American Chemical Society

Triazine-Substituted Zinc Porphyrin as an Electron Transport Interfacial Material for Efficiency Enhancement and Degradation Retardation in Planar Perovskite Solar Cells

Motivated by the excellent electron-transfer capability of porphyrin molecules in natural photosynthesis, we introduce here the first application of a porphyrin compound to improve the performance of planar perovskite solar cells. The insertion of a thin layer consisting of a triazine-substituted Zn porphyrin between the TiO₂ electron transport layer and the CH₃NH₃PbI₃ perovskite film significantly augmented electron transfer toward TiO₂ while also sufficiently improved the morphology of the perovskite film. The devices employing porphyrin-modified TiO₂ exhibited a significant increase in the short-circuit current densities and a small increase in the fill factor. As a result, they delivered a maximum power conversion efficiency (PCE) of 16.87% (average 14.33%), which represents a 12% enhancement compared to 15.01% (average 12.53%) of the reference cell. Moreover, the porphyrin-modified cells exhibited improved hysteretic behavior and a higher stabilized power output of 14.40% compared to 10.70% of the reference devices. Importantly, nonencapsulated perovskite solar cells embedding a thin porphyrin interlayer showed an elongated lifetime retaining 86% of the initial PCE after 200 h, while the reference devices exhibited higher efficiency loss due to faster decomposition of CH₃NH₃PbI₃ to PbI₂