Optical technologies allowing modulation of neuronal activity at high spatio-temporal resolution are becoming paramount in neuroscience. In this respect, azobenzene-based photoswitches are promising ...nanoscale tools for neuronal photostimulation. Here we engineered a light-sensitive azobenzene compound (Ziapin2) that stably partitions into the plasma membrane and causes its thinning through trans-dimerization in the dark, resulting in an increased membrane capacitance at steady state. We demonstrated that in neurons loaded with the compound, millisecond pulses of visible light induce a transient hyperpolarization followed by a delayed depolarization that triggers action potential firing. These effects are persistent and can be evoked in vivo up to 7 days, proving the potential of Ziapin2 for the modulation of membrane capacitance in the millisecond timescale, without directly affecting ion channels or local temperature.
Over the past few years the liquid scintillation technique employed for particle detection applications has undergone a significant technological breakthrough with the introduction of novel solvents ...tailored to address the concerns about toxicity, flammability and disposal problems associated with the scintillators of traditional formulation.
The increasing popularity of the new solvents in the realization of experimental set-ups of various degrees of size and complexity implies the need of a thorough study and characterization of the features of the corresponding scintillation mixtures, with the aim to approach eventually a level of understanding similar to that, very accurate, achieved throughout many years of research for the scintillators realized with conventional solvents.
In this general context, aim of this work is to illustrate the results of the fluorescence decay time and pulse shape discrimination measurements carried out on a set of scintillation mixtures realized using two of such novel solvents, i.e., linear alkylbenzene (LAB) and di-isopropylnaphthalene (DIN). The measurements have been performed either under particle or UV excitation of the scintillating solutions, which permitted to unravel the features both of the fast component and of the long tail forming the entire scintillation pulse.
Moreover, the particle characterization via β or α excitation allows also predicting the α⧸β pulse shape discrimination capability of the mixtures, a property of paramount significance for applications focused on the increasingly important field of low background detectors.
This paper reviews a series of photochromic systems belonging to the classes of spirooxazines, chromenes and arylethenes, which have been recently investigated in our laboratory. Temperature ...variations may have very significant and different effects on the behaviour of photochromic systems, which depend on their type of reversibility (T or P systems). For thermoreversible photochromic molecules, increasing the temperature increases the rate of the thermal bleaching reaction, thus decreasing light-stimulated colouration. For systems being both photochromic and thermochromic, such as spirooxazines and chromenes, a combination of the experimental data gathered from temperature effect studies can bring about a complete description of the kinetics and thermodynamics of the ground state reaction, in terms of activation energies, frequency factors, thermodynamic activation parameters, equilibrium constants of the ground state reaction. Lowering the temperature may either reduce a complex photochemical reaction, which yields several photoproducts, to a simpler one giving a single photoproduct, as observed for some chromenes, or transform a thermo- and photoreversible system into one which is only photoreversible, as found for some dipyrrolylperfluorocyclopentenes: thermal decolouration dominates bleaching at room temperature and above; whilst at low temperature thermostability and photoreversibility are established. For photoreversible systems, such as photochromic arylethenes, the quantum yields for both UV colouration, Φ
O→C, and visible decolouration, Φ
C→O, were found to depend on the temperature. An in depth understanding of the reaction mechanisms and the design of synthetic strategies for possible practical applications entail a careful analysis of all of these aspects.
► Temperature influences the spectrokinetic and mechanistic sides of photochromism. ► Thermochromism helps defining the thermodynamics of the photochromic reaction. ► Lowering the temperature may simplify a complex photochemical reaction. ► Temperature variations can transform a T and P photochromic system into a P one. ► The quantum yields of colouration and decolouration depend on the temperature.
•Proximity effects on photophysics and photochemistry of heteroaromatic ketones.•Excited state properties modulated by lowest triplet states n,π* or π,π* character.•Energetics and dynamics governed ...by the number and position of heteroaromatics.
Although the photophysics and photochemistry of aromatic carbonyl compounds have been extensively studied over several years, the interest in their photobehaviors is still alive and they continue to be investigated by exploiting advanced experimental and computational technologies. In this article complete series of pyridyl, di-pyridyl, thienyl, di-thienyl and thienyl-pyridyl ketones are reviewed, mainly from the spectroscopic and photochemical points of view. Properties and reactivity of their excited states have been investigated through stationary absorption and emission spectra, time resolved transient spectroscopy, dynamic luminescence techniques and computational methods. The results reported demonstrate that the photophysics and photochemistry of these molecules can be modulated by changing the rings linked to the carbonyl (pyridyl, thienyl, phenyl) and their linking position, as also the microenvironment where they are included. Of special importance are their properties of triplet photosensitizers and their ability in photogenerating free radicals. Enhancing or depressing such properties may be required in applications and this can be achieved by structure and environment changes.
A recently synthesized and structurally characterized bisdiarylethene containing a benzobis(imidazole) core substituted with two aniline moieties has been investigated from spectroscopic, ...thermodynamic, and photochemical points of view, using both experimental and theoretical tools. Due to the presence of four basic centers and of two photochromic diarylethenes in the molecular structure, the solutions of this compound change color upon acid addition and/or UV irradiation. Neutralization and/or visible irradiation lead to bleaching. In a water/dioxane (1/1, v/v) mixture, pK a values and absorption spectra of the open and closed neutral and protonated species, as well as quantum yields of the photochromic cyclization and cycloreversion processes, have been determined at selected pH/H 0 values by spectrophotometric and photostationary spectrokinetic methods. Time-dependent density functional theory simulations have been carried out and provide insight into the protonation sites and photochromic properties. The results show that the four acidity constants overlap within a restricted pH/H 0 interval (4.5/–1.5) generating spectra of the colorless and colored forms that progressively shift toward the red. The possibility of continuously tuning the color of the solutions by external stimuli, such as irradiation and acidification, generates a multiswitchable acidichromic and photochromic material.
Spirooxazines are well-known photochromic dyes that, upon proper illumination, convert between uncolored/coloured forms. In order to take advantage of their photoswitchable properties, one strategy ...is represented by their encapsulation in transparent host matrices, like polymers, which may improve the performance of the material, thanks to a major protection from oxidative degradation, or induce a variation of the optical properties, since the photochromic systems are affected by the surrounding environment. The fine-tuning and the strict control of the photochromic behaviour of the polymeric films is extremely appealing for several purposes, going from optical switches to sensors and light harvesting devices.
One of the most elegant ways to exploit the photochromic characteristic of these materials is the controlled switch of the colour and the colouring/bleaching rate of a single photochromic system, since this versatility can open the possibility to use the same material for different applications.
Therefore, a study of the modulation of the colourability and the colouring/bleaching rates of two spirooxazines in different polymeric matrices is herein reported. The influence of the photochromic concentration and the chemical nature of the polymeric matrix on the photophysical behaviour of the proposed systems is investigated to achieve a photochromic/polymeric dual system with tailored properties.
The optical characterization of increasing concentrations of photochromic compound in solution was essential for the design of colour-defined polymeric films, highlighting, indeed, a correlation between photochromic concentration and colour switching from blue to pink, effect assigned to formation of aggregate species.
By the proper choice of photochromic concentration and polymeric matrix, solid films showing great photoconversion efficiency and different colours were achieved under irradiation, together with the possibility to modulate the bleaching rate from few seconds to tens of minutes. Furthermore, polymeric films with different colours before irradiation could be produced as well.
The obtained results open the possibility of a multi-purpose use of a photochromic system by simply varying its concentration within the polymeric film. Moreover, interesting colouring effect can be obtained by changing the polymeric matrix, therefore further widening their applicability.
•A multi-purpose photochromic system was designed by the proper tuning of molecular concentration within a polymeric matrix.•Thin solid films having great photoconversion efficiency were obtained, with bleaching rates ranging from seconds to minutes.•The formation of molecular aggregates, dependent on the nature of the polymer, yielded interesting colouring effects.
New Thermally Irreversible and Fluorescent Photochromic Diarylethenes Cipolloni, Marco; Ortica, Fausto; Bougdid, Lahoussine ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
05/2008, Letnik:
112, Številka:
21
Journal Article
Recenzirano
A photokinetic investigation is here carried out on four newly synthesized diarylethenes with the aim to test their performance as photoreversible chromogenic and light emitting materials. The ...pentatomic ring, which fixes these diarylethenes in the cis conformation, contains a Si atom or a PO group. The 1,2 positions at the ethenic bond are symmetrically substituted with thienyl or benzothienyl groups. The results are compared with those for the structurally related and widely studied 1,2-bis(2-methyl-benzobthiophen-3-yl)perfluorocyclopentene (BTF6), investigated here under the same experimental conditions. Spectra of the colorless and colored forms and photoreaction quantum yields were determined; temperature, excitation wavelength and viscosity effects were explored. Compounds containing benzothienyl substituents were found to be good bistable photochromes, with high photochemical yields of both the cyclization and cycloreversion reactions, and to display appreciable fluorescence emission from the colored forms, which is a rare and desirable property for photochromes. In contrast, the molecules not bearing the benzene condensed rings were found unsuitable as photochromes because of side degradation processes occurring in competition with cyclization.
In this work, the interaction of a naturally occurring chromene, flindersine (FL), and bovine serum albumin (BSA) has been investigated by UV−vis absorption and fluorescence spectroscopy, ...time-resolved lifetime measurements, steady state photochemistry, and semiempirical calculations. The interplay of FL with tryptophan (Trp) has been studied in parallel. The interaction of FL with BSA causes fluorescence quenching of BSA through both static and dynamic quenching mechanisms. FL binds BSA with a stoichiometry that varies from 1.09:1 to 0.80:1 as the temperature increases from 293 to 308 K. The reaction is characterized by negative enthalpy (ΔH° = −193 kJ mol−1) and negative entropy (ΔS° = −550 J K−1 mol−1), indicating that the predominant forces in the FL−BSA complex are hydrogen bonding and van der Waals forces. The binding distance between the protein and the photochrome was calculated as 2.5 nm, according to the Foerster theory on resonance energy transfer. The effect of FL concentration on the BSA fluorescence was analyzed according to the maximum entropy method. FL also quenches the emission of Trp with a mechanism that, based on the experimental evidence, excludes both static and dynamic effects. An alternative relaxation pathway, consisting in an electron transfer from a prefluorescent state of Trp to FL, is put forward. The photobehavior of FL is affected by the interplay with BSA but not with Trp. When FL is complexed with BSA, it becomes a more fluorescent and more reactive species. Semiempirical calculations of the lowest optically active electronic transitions of hypothetical FL photoproducts suggest the most likely structure for the photoproduct.
•A novel photochromic (PC) film was developed and tested for smart windows.•Building integration in a standard medium office building was modelled.•Energy saving were assessed, comparing PC glazing ...with standard compliant glazing.•Up to 4 MWh/year of energy saving and 40% of visual comfort increase were reached.•The dynamic behaviour of the PC film is the best choice for visual comfort.
The study of chromogenic materials and systems is particularly promising for innovative, transparent building envelopes, with thermo-optical properties adaptable to surrounding environmental conditions. This work spots light on the multiple effects of photochromic glazing on the energy consumption of buildings and on the impact that such technologies would have on the visual comfort of occupants. To our knowledge, this is the first work dealing with building integration of spirooxazine-based photochromic films. This experimental and theoretical work aims helping to fill this gap by reporting the results of a study concerning the spirooxazine photochromic molecules, integrated in transparent matrices of polymethylmethacrylate. This work discloses the potential of specific photochromic materials, especially as a function of spectral peculiarities. The figures of merit of this technology have been studied by assuming its integration in an ideal multi-storey office building, and by studying the effects in terms of energy consumption and visual comfort and proposing a comparison with several static commercial glazing technologies. The photochromic glazing demonstrated to offer significant reduction of energy use for cooling, compared to a clear glass (with yearly saving of 4079 kWh, on the Southern facade), and for artificial lighting (with a saving of 3711 kWh), if compared to the commercial solar control glazing. Furthermore, the dynamic behaviour of the photochromic glazing represented the best choice in terms of visual comfort.
The role played by the carbonyl group in the antenna system of a naturally occurring photochromic chromene, flindersine (FL), has been experimentally investigated and compared with that of a carbonyl ...group present in a structurally related unreactive heterocyclic compound, 6(5H)-phenanthridinone (PH). Through stationary and time-resolved absorption and emission techniques, the excited-state relaxation dynamics after UV irradiation were determined for FL and PH. The presence of a carbonyl group in both compounds entails the existence of two close-lying, strongly coupled electronic excited states, having n,π* and π,π* character, respectively. Their coupling can be modulated by a careful choice of the solvent proticity and temperature. Moreover, in the case of strong coupling between the n,π* and π,π* states, we have proved that the relaxation dynamics can involve transitions in which the upper of the coupled states acts as an intermediate for radiationless decay, bypassing the lowest emissive state, whereby the fluorescence quantum yield becomes a function of the excitation wavelength.
