Engineering Metal Halide Perovskite Nanocrystals with BODIPY Dyes for Photosensitization and Photocatalytic Applications.

The sensitization of surface-anchored organic dyes on semiconductor nanocrystals through energy transfer mechanisms has received increasing attention owing to their potential applications in photodynamic therapy, photocatalysis, and photon upconversion. Here, we investigate the sensitization mechanisms through visible-light excitation of two nanohybrids based on CsPbBr3 perovskite nanocrystals (NC) functionalized with borondipyrromethene (BODIPY) dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP), named as NC@BDP and NC@I2-BDP, respectively. The ability of I2-BDP dyes to extract hot hole carriers from the perovskite nanocrystals is comprehensively investigated by combining steady-state and time-resolved fluorescence as well as femtosecond transient absorption spectroscopy with spectroelectrochemistry and quantum chemical theoretical calculations, which together provide a complete overview of the phenomena that take place in the nanohybrid. Förster resonance energy transfer (FRET) dominates (82%) the photosensitization of the singlet excited state of BDP in the NC@BDP nanohybrid with a rate constant of 3.8 ± 0.2 × 1010 s-1, while charge transfer (64%) mediated by an ultrafast charge transfer rate constant of 1.00 ± 0.08 × 1012 s-1 from hot states and hole transfer from the band edge is found to be mainly responsible for the photosensitization of the triplet excited state of I2-BDP in the NC@I2-BDP nanohybrid. These findings suggest that the NC@I2-BDP nanohybrid is a unique energy transfer photocatalyst for oxidizing α-terpinene to ascaridole through singlet oxygen formation.

The role of the oxime group in the excited state deactivation processes of indirubin.

The introduction of an oxime group into indirubin (INR) derivatives, including INROx, MINROx, and 6-BrINROx, and its impact on the spectral and photophysical properties of INR was investigated using a combination of fast-transient absorption (fs-TA/fs-UC) and steady-state fluorescence techniques. The oxime group introduces structural modifications that promote a rapid keto-enol tautomeric equilibrium and enhance the excited-state proton transfer (ESPT) process compared to its analogue, INR. In the oxime-indirubin derivatives investigated, the ESPT process is notably more efficient than what is observed in INR and indigo, occurring extremely fast (<1 ps) in all solvents, except for the viscous solvent glycerol. The more rapid deactivation mechanism precludes the formation of an intermediate species (syn-rotamer), as observed with INR. These findings are corroborated by time-dependent density functional theory (TDDFT) calculations. The work demonstrates that introducing an oxime group to INR, whether in nature or in the laboratory, results in an enhancement of its photostability.

Solvent-Driven Self-Organization of Meso-Substituted Porphyrins: Morphological Analysis from Fluorescence Lifetime Imaging Microscopy.

A morphological analysis of different thin films of meso-tetra-p-(di-p-phenylamino)phenylporphyrin, H2T(TPA)4P, was made by fluorescence lifetime imaging microscopy (FLIM) and scanning electron microscopy (SEM). A comprehensive study of H2T(TPA)4P was undertaken through UV/vis absorption and fluorescence techniques in different solvents, solvent mixtures and in thin films. In solution, occurrence of intramolecular energy transfer from the triphenylamine (TPA) moieties to the porphyrin core, with quenching efficiencies in the order of 94-97%, is observed. The energy transfer rate constants are determined assuming Förster's dipole-dipole and Dexter's electron exchange mechanisms. In drop-cast-prepared thin films, from samples with different solvent mixtures, the photoluminescence (PL) quantum yield (ΦPL) decreases ∼1 order of magnitude compared to the solution behavior. FLIM and SEM experiments showed the self-organization and morphology of H2T(TPA)4P in thin films to be highly dependent on the solvent mixture used to prepare the film. In chloroform, the solvent's evaporation results in the formation of elongated and overlapped microrod structures. Introduction of a cosolvent, namely, a polar cosolvent, promotes changes in the morphology of the self-assembled structures, with the formation of three-dimensional spherical structures and hollow spheres. H2T(TPA)4P dispersed in a polymer matrix shows enhanced ΦPL values when compared to the drop-cast films. FLIM images showed coexistence of three different states or domains: aggregated, interface, and nonaggregated or less-aggregated states. This work highlights the importance of FLIM in the morphological characterization of heterogeneous films, together with the photophysical characterization of nano- and microdomains.

The role of solvents and concentrations in the properties of oxime bearing A2B corroles.

A comprehensive study on the electronic spectral, photophysical and acid-base properties of phenyl- and methyl-oxime corrole derivatives and of triphenylcorrole (model corrole) has been performed, aiming to shed light on the existing species in the ground and excited states. Solvents and corrole concentration are found to govern the properties of the studied compounds and are determinants of their applicability in in vivo studies. In THF, the neutral corrole has two tautomeric forms (T1 and T2). In DMSO, the deprotonated form shows a characteristic long-wavelength Q band slightly shifted to blue when compared with the T1 tautomer and a higher fluorescence quantum yield. In ACN, with the increase of the corrole concentration formation of an aggregate due to homoconjugation (with dimer characteristics) is observed, and pioneeringly reported using UV-Vis and fluorescence studies and confirmed by carrying out titrations with TFA. The effect of the oxime group on the pK values of a corrole is found to influence the formation of a homoconjugate, namely by precluding its formation (at higher concentrations) when compared with the model corrole. TDDFT electronic quantum calculations support the experimental observations, namely the existence of tautomers and deprotonated species, with their respective electronic spectral features, further allowed proposing a structure for the homoconjugate complex in ACN. The characteristics of the oxime-corroles, namely a pK of ∼ 5, absorption and emission at ca. 650 nm and solvent dependent properties, make them good candidates for their use in biological systems either as probes, sensors, or as new sensitizers for photodynamic therapy.

Magnesium maintains the length of the circadian period in Arabidopsis.

The circadian clock coordinates the physiological responses of a biological system to day and night rhythms through complex loops of transcriptional/translational regulation. It can respond to external stimuli and adjust generated circadian oscillations accordingly to maintain an endogenous period close to 24 h. However, the interaction between nutritional status and circadian rhythms in plants is poorly understood. Magnesium (Mg) is essential for numerous biological processes in plants, and its homeostasis is crucial to maintain optimal development and growth. Magnesium deficiency in young Arabidopsis thaliana seedlings increased the period of circadian oscillations of the CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) promoter (pCCA1:LUC) activity and dampened their amplitude under constant light in a dose-dependent manner. Although the circadian period increase caused by Mg deficiency was light dependent, it did not depend on active photosynthesis. Mathematical modeling of the Mg input into the circadian clock reproduced the experimental increase of the circadian period and suggested that Mg is likely to affect global transcription/translation levels rather than a single component of the circadian oscillator. Upon addition of a low dose of cycloheximide to perturb translation, the circadian period increased further under Mg deficiency, which was rescued when sufficient Mg was supplied, supporting the model's prediction. These findings suggest that sufficient Mg supply is required to support proper timekeeping in plants.

Aggregation-Induced Emission Leading to White Light Emission in Diphenylbenzofulvene Derivatives.

The search for a unique molecular system able to efficiently emit in the total visible range of the electromagnetic spectra, i. e., white light emission (WLE), is a topic of intense research. We here show that aggregates formed by diphenylbenzofulvene (DPBF) derivatives are from two to four orders of magnitude more emissive than their monomers. From a simple strategy, involving structural modification of a DPBF propelled shape core, a close match with the pure white light emission coordinates is obtained with a combination of two derivatives in films, with featured solid-state emission, without involvement of D-A groups or energy transfer processes.

Tryptanthrin derivatives as efficient singlet oxygen sensitizers.

Halogenated tryptanthrin and aminotryptanthrin were synthesized from indigo or isatin precursors. Dibromo- and tetrabromo-tryptanthrin were obtained from indigo dyes following green chemistry procedures, through microwave-assisted synthesis in mild oxidation conditions. Spectral and photophysical properties of the compounds, including quantitative determination of all the different deactivation pathways of S1 and T1, were obtained in different solvents and temperatures. The triplet state (T1) has a dominant role on the photophysical properties of these compounds, which is further enhanced by the halogens at the fused-phenyl rings. Substitution with an amino group, 2-aminotryptanthrin (TRYP-NH2), leads a dominance of the radiative decay channel. Moreover, with the sole exception of TRYP-NH2, S1 ~ ~ > T1 intersystem crossing constitutes the dominant route, with internal conversion playing a minor role in the deactivation of S1 in all the studied derivatives. In agreement with tryptanthrin, emission of the triplet state of tryptanthrin derivatives (with exception of TRYP-NH2), was observed together with an enhancement of the singlet oxygen sensitization quantum yield: from 70% in tryptanthrin to 92% in the iodine derivative. This strongly contrasts with indigo and its derivatives, where singlet oxygen sensitization is found inefficient.

Aggregation-Induced Emission with Alkynylcoumarin Dinuclear Gold(I) Complexes: Photophysical, Dynamic Light Scattering, and Time-Dependent Density Functional Theory Studies.

Aggregation-induced emission (AIE) has gained a remarkable amount of interest in the past 20 years, but the majority of the studies are based on organic structures. Herein, three dinuclear gold(I) complexes, with the general formula [PPh2XPPh2-Au2-Coum2], where the Au(I) atom is linked to three different diphosphanes [PPh2XPPh2; DPPM for X = CH2 (1.1), DPPP for X = (CH2)3 (1.2), and DPPA for X = C≡C (1.3)] and the propynyloxycoumarin precursor (1, 4-methyl-substituted coumarin), have been synthesized. The compounds present AIE characteristics, AIEgens, with high luminescence quantum yields in the solid state when they are compared to dilute solutions. Photophysical studies (steady-state and time-resolved fluorescence) were obtained, with AIE being observed with the three gold(I) complexes in acetonitrile/water mixtures. This was further corroborated with dynamic light scattering measurements. Time-dependent density functional theory (TDDFT) electronic calculations show that the compounds have different syn and anti conformations (relative to the coumarin core) with 1.1 syn and 1.2 and 1.3 both anti. From time-resolved fluorescence experiments, the augment in the contribution of the longer decay component is found to be associated with the emission of the aggregate (AIE effect) and its nature (involving a dimer) rationalized from TDDFT electronic calculations.

Excited state deactivation mechanisms in Shikonin rationalized from its naphthoquinone parent structures.

Shikonin, a naphthoquinone dye, is a molecule of colour of natural origin, whose peculiar properties have not yet been fully rationalized. Its core structure consists of a di-hydroxy-naphthoquinone with an additional non-aromatic hydroxy group. From a comprehensive study involving fast spectroscopic techniques (fs-TA and fs-UC) and TDDFT electronic structure calculations on shikonin (Shk) and its derivatives 5-hydroxy-1,4-naphthoquinone (5HNQ), 5,8-diacetoxy-1,4-naphthoquinone (DiAc), 5,8-dihidroxy-1,4-naphthoquinone (DHNQ) and acetylshikonin, AcShk, it is shown that intramolecular excited state proton transfer (ESIPT) is present and is determinant in the deactivation of the hydroxy containing molecules. This is mirrored by the dominance of the internal conversion deactivation channel. In Shk, the non-aromatic hydroxy group determines the preferred conformer in both the ground- and excited-state, as reflected in the doubling of the fluorescence quantum yield value of this molecule relative to DHNQ. From fs-UC, a kinetic isotopic effect of 1.7 was obtained for DHNQ.

Cucurbituril hosts as promoters of aggregation induced emission of triphenylamine derivatives.

Three ligands bearing triphenylamine as a core and one, two or three acyclic polyamine chains, TPA1p, TPA2p and TPA3p, respectively, have been studied by potentiometric and photophysical (UV-Vis, steady-state and time-resolved fluorescence) techniques. The host-guest interaction with cucurbit[7]uril, CB7, has been investigated in aqueous solution showing aggregation induced emission behaviour when encapsulated into a CB7 cavity. From fluorescence emission it is revealed that the charged polyamine chains are the unit entering into CB7 and from the Job plots the stoichiometries are found to vary from 1 : 1 to 1 : 3 L : CB7 ratios. Interactions of the charged amines with the portals of CB7 restrict rotation of the benzene units in the triphenylamine backbone (free rotor effect), decreasing the radiationless internal conversion channel at the expense of the enhancement of fluorescence. Dynamic light scattering and resonance Rayleigh scattering experiments show that TPA3p-CB7 complexes involve formation of aggregates with a mean size of 126 ± 5 nm and a dispersity factor of 0.117, indicating a monodisperse distribution and supporting the important conclusions of this work: formation of emissive aggregates through the AIE effect.

Tuning J-aggregate Formation and Emission Efficiency in Cationic Diazapentacenium Dyes.

Enhancement of the luminescence efficiency of two new diazapentacenium salts (D1 and D2) of more than 55 for D1 and 22 times for D2) in poor solvents, acetonitrile and/or dichloromethane, was observed and rationalized as formation of emissive J-aggregates. Both compounds displaying 4-n-decylphenyl substituents at the 7,14-carbons and phenyl (D1) or 2,6-difluorophenyl (D2) substituents at the quaternary nitrogen atoms in 5,12-positions have been synthetized in a two-step procedure involving a two-fold Buchwald-Hartwig-type CN cross-coupling and an electrophilic Friedel-Crafts-type cyclization. The optical properties of the dicationic diazapentacenium salts in various solvents and in thin films have been investigated by steady-state and time-resolved absorption and photoluminescence spectroscopies. In thin films and in good solvents, isolated molecules coexist with aggregates. Nonetheless, D1 is seven times more emissive than D2, reflecting a higher J-aggregate contribution in the former.

Cationic Diazapentacenium Polymers Made in a Sequence of CN Cross Coupling Polymerization and Acid-Mediated Postpolymerization Cyclization.

Polycationic stepladder polymers containing 5,12-diazapentacenium bistriflate repeat units are made in a two-step sequence of a carbon-nitrogen cross coupling polymerization and subsequent postpolymerization cyclization. The deeply colored products show a rather weak conjugative interaction between the dicationic diazapentacenium repeat units along the polymer chains.

Endoplasmic reticulum-localized CCX2 is required for osmotolerance by regulating ER and cytosolic Ca2+ dynamics in Arabidopsis.

Ca2+ signals in plant cells are important for adaptive responses to environmental stresses. Here, we report that the Arabidopsis CATION/Ca2+ EXCHANGER2 (CCX2), encoding a putative cation/Ca2+ exchanger that localizes to the endoplasmic reticulum (ER), is strongly induced by salt and osmotic stresses. Compared with the WT, AtCCX2 loss-of-function mutant was less tolerant to osmotic stress and displayed the most noteworthy phenotypes (less root/shoot growth) during salt stress. Conversely, AtCCX2 gain-of-function mutants were more tolerant to osmotic stress. In addition, AtCCX2 partially suppresses the Ca2+ sensitivity of K667 yeast triple mutant, characterized by Ca2+ uptake deficiency. Remarkably, Cameleon Ca2+ sensors revealed that the absence of AtCCX2 activity results in decreased cytosolic and increased ER Ca2+ concentrations in comparison with both WT and the gain-of-function mutants. This was observed in both salt and nonsalt osmotic stress conditions. It appears that AtCCX2 is directly involved in the control of Ca2+ fluxes between the ER and the cytosol, which plays a key role in the ability of plants to cope with osmotic stresses. To our knowledge, Atccx2 is unique as a plant mutant to show a measured alteration in ER Ca2+ concentrations. In this study, we identified the ER-localized AtCCX2 as a pivotal player in the regulation of ER Ca2+ dynamics that heavily influence plant growth upon salt and osmotic stress.

Room-Temperature Phosphorescence and Efficient Singlet Oxygen Production by Cyclometalated Pt(II) Complexes with Aromatic Alkynyl Ligands.

The synthesis of five novel cyclometalated platinum(II) compounds containing five different alkynyl-chromophores was achieved by the reaction of the previously synthesized Pt-Cl cyclometalated compound (1) with the corresponding RC≡CH by a Sonogashira reaction. It was observed that the spectral and photophysical characteristics of the cyclometalated platinum(II) complexes (Pt-Ar) are essentially associated with the platinum-cyclometalated unit. Room-temperature emission of the Pt-Ar complexes was attributed to phosphorescence in agreement with DFT calculations. Broad nanosecond (ns)-transient absorption spectra were observed with decays approximately identical to those obtained from the emission of the triplet state. From the femtosecond-transient absorption (fs-TA) data, two main excited-state decay components were identified: one in the order of a few picoseconds was assigned to fast intersystem crossing to populate the triplet excited-state and the second (hundreds of ns) was associated with the decay of the transient triplet state. In general, efficient singlet oxygen photosensitization quantum yields were observed from the triplet state of these complexes.

Interactions and Supramolecular Organization of Sulfonated Indigo and Thioindigo Dyes in Layered Hydroxide Hosts.

Supramolecularly organized host-guest systems have been synthesized by intercalating water-soluble forms of indigo (indigo carmine, IC) and thioindigo (thioindigo-5,5'-disulfonate, TIS) in zinc-aluminum-layered double hydroxides (LDHs) and zinc-layered hydroxide salts (LHSs) by coprecipitation routes. The colors of the isolated powders were dark blue for hybrids containing only IC, purplish blue or dark lilac for cointercalated samples containing both dyes, and ruby/wine for hybrids containing only TIS. The as-synthesized and thermally treated materials were characterized by Fourier transform infrared, Fourier transform Raman, and nuclear magnetic resonance spectroscopies, powder X-ray diffraction, scanning electron microscopy, and elemental and thermogravimetric analyses. The basal spacings found for IC-LDH, TIS-LDH, IC-LHS, and TIS-LHS materials were 21.9, 21.05, 18.95, and 21.00 Å, respectively, with intermediate spacings being observed for the cointercalated samples that either decreased (LDHs) or increased (LHSs) with increasing TIS content. UV-visible and fluorescence spectroscopies (steady-state and time-resolved) were used to probe the molecular distribution of the immobilized dyes. The presence of aggregates together with the monomer units is suggested for IC-LDH, whereas for TIS-LDH, IC-LHS, and TIS-LHS, the dyes are closer to the isolated situation. Accordingly, while emission from the powder H2TIS is strongly quenched, an increment in the emission of about 1 order of magnitude was observed for the TIS-LDH/LHS hybrids. Double-exponential fluorescence decays were obtained and associated with two monomer species interacting differently with cointercalated water molecules. The incorporation of both TIS and IC in the LDH and LHS hosts leads to an almost complete quenching of the fluorescence, pointing to a very efficient energy transfer process from (fluorescent) TIS to (nonfluorescent) IC.

Deactivation Routes in Gold(I) Polypyridyl Complexes: Internal Conversion Vs Fast Intersystem Crossing.

An electronic spectral and photophysical characterization of three gold(I) complexes containing heterocyclic chromophores differing in the number and arrangement of pyridine rings (pyridine, bipyridine, and terpyridine, with the acronyms pD, bD, and tD respectively) was performed. Quantum yields of fluorescence, internal conversion and triplet state formation, together with the rate constants for singlet to triplet intersystem crossing, S1 ∼ ∼ ∼ S0 internal conversion and fluorescence were measured in order to equate the impact of fast triplet state formation on the amount of triplets formed. The results showed a correlation between the increase on the measured decay values of S1 (leading to the main formation of T1) and the increase in the charge transfer (CT) character of the lowest energy transition, as evaluated from the orthogonality of the frontier orbitals. The measured triplet state quantum yields range from ∼50-60% to 70%, whereas the intersystem crossing rate constants differ by almost 2 orders of magnitude, from 9.4 × 109 s-1 for tD to 8.1 × 1011 s-1 for bD. This constitutes an evidence for the existence of a correlation between the intersystem crossing and the internal conversion mechanisms.

Relationships between soil and leaf mineral composition are element-specific, environment-dependent and geographically structured in the emerging model Arabidopsis halleri.

Leaf mineral composition, the leaf ionome, reflects the complex interaction between a plant and its environment including local soil composition, an influential factor that can limit species distribution and plant productivity. Here we addressed within-species variation in plant-soil interactions and edaphic adaptation using Arabidopsis halleri, a well-suited model species as a facultative metallophyte and metal hyperaccumulator. We conducted multi-element analysis of 1972 paired leaf and soil samples from 165 European populations of A. halleri, at individual resolution to accommodate soil heterogeneity. Results were further confirmed under standardized conditions upon cultivation of 105 field-collected genotypes on an artificially metal-contaminated soil in growth chamber experiments. Soil-independent between- and within-population variation set apart leaf accumulation of zinc, cadmium and lead from all other nutrient and nonessential elements, concurring with differential hypothesized ecological roles in either biotic interaction or nutrition. For these metals, soil-leaf relationships were element-specific, differed between metalliferous and nonmetalliferous soils and were geographically structured both in the field and under standardized growth conditions, implicating complex scenarios of recent ecological adaptation. Our study provides an example and a reference for future related work and will serve as a basis for the molecular-genetic dissection and ecological analysis of the observed phenotypic variation.