The photobehavior of five photochromic dipyrrolyl-perfluoro-cyclopentenes was studied by steady state and time-resolved absorption spectroscopy. The quantum yields of the UV-photoinduced ring-closing ...reaction (coloration) and the visible-stimulated cycloreversion reaction (bleaching) were measured. Kinetic and thermodynamic parameters of thermal bleaching were also determined. Nanosecond time-resolved experiments showed formation of a transient, which was not a precursor of the reaction photoproduct. This transient was tentatively assigned to a radical cation formed by direct photoionization through a short-lived triplet state. The nature of the transient species was supported by photoinduced electron transfer to electron acceptors.
The steady-state and time-resolved photoluminescence of nine ternary solid solutions, whose general formula is La2xGa2yIn2zO3, used as heterogeneous photocatalysts for the production of hydrogen by ...water splitting, has been investigated in order to characterize the properties of their electronic excited states. The comparison with the parent binary oxides (LaGaO3, LaInO3 and GaInO3) proved to be essential for understanding the composition of the solids in terms of phases and allowed the different emissions to be assigned to specific crystal structures and band gap transitions. Upholding what was previously deduced by means of the X-ray powder diffraction and micro-Raman techniques, the structural properties of the La2xGa2yIn2zO3 samples were corroborated. By doing so, the employment of photoluminescence as a distinctive feature to strengthen the structural information gathered by other techniques is demonstrated. Moreover, the luminescence lifetimes of the photo-generated electron–hole pairs were measured and analyzed in view of the photocatalytic activity of the samples, with their efficiency being directly proportional to the excited state lifetime. Finally, the metal oxides solid solutions have been found able to emit over the entire visible region up to near-IR. Therefore, they might be appealing panchromatic emitters for display and lightning technologies.
•The photoluminescence is useful to gain insight on structural composition of solid solutions.•Determination of electronic lifetimes by both Least-Squares and Maximum Entropy method.•Direct electronic transitions last less than indirect phonon-assisted transitions.•La2xGa2yIn2zO3 are promising panchromatic emitters.•La2xGa2yIn2zO3 have lifetimes ranging from tens of μs up to tens of ms.
A photophysical and photochemical study of a biphotochromic compound where two naphthopyran units are linked by an acetylene–thiophene–acetylene bridge has been carried out in toluene. Both ...fluorescence and intersystem crossing to the triplet manifold were found to compete with the photocoloration process. Two photoproducts (transoid-trans and transoid-cis stereoisomers), absorbing at ∼480 nm and corresponding to the opening of a single photochromic unit, were detected by spectrophotometric analysis after short irradiation time in diluted solution and identified by 1H–nuclear magnetic resonance (NMR) spectroscopy. After prolonged irradiation at 228 K of highly concentrated solutions (up to 3 × 10−3 mol dm−3), two additional isomers, absorbing at ∼550 nm, were formed. Their NMR spectra indicate the opening of both photochromic units. An interesting effect of selective vibronic excitation was found, showing that the photoreaction is favored at excited vibronic levels to the detriment of the radiative relaxation.
We present an unusual upconversion process based on the sensitized triplet–triplet annihilation where the triplet energy of the donor exceeds that of the acceptor. Either a palladium ...octaethyl-porphyrin (PdOEP) or a platinum octaethyl-porphyrin (PtOEP) are the sensitizers, whereas tetraphenyl-pyrene (TPPy) is the emitter. The two couples convert the green to violet light in deoxygenated toluene with different efficiencies. The quantum yields of the upconversion processes (ΦUC) were calculated at different concentrations and intensities. We focused on low power non-coherent irradiation to simulate the solar energy supply. To demonstrate the important role played by the rate of the energy transfer from sensitizer to emitter in optimizing ΦUC, we tested the effect of the substitution of TPPy with 9,10-diphenylanthracene.
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►Green to violet upconversion, based on a triplet–triplet annihilation process. ► Upconversion involving a porphyrin, an aromatic hydrocarbon, and incoherent light. ► Unusual energetically hindered and entropically driven upconversion phenomenon. ► Effect of concentrations of sensitizer and emitter on the upconversion intensity. ► Role of the triplet energies of the molecular pair.
In this work, we present the hydrogen production by photolysis, sonolysis and sonophotolysis of water in the presence of newly synthesized solid solutions of rare earth, gallium and indium oxides ...playing as catalysts. From the experiments of photolysis, we found that the best photocatalyst is the solid solution Y0.8Ga0.2InO3 doped by sulphur atoms. In experiments of sonolysis, we optimized the rate of hydrogen production by changing the amount of water, adding ethanol and tuning the power of our piezoelectric transducer. Finally, we performed sonolysis and sonophotolysis experiments in the presence of S:Y0.8Ga0.2InO3 finding a promising synergistic effect of UV-visible electromagnetic waves and 38 kHz ultrasound waves in producing H2.
Two chloromethyl phenylcarbamate‐based chiral stationary phases, one containing an amylose‐type chiral selector (Lux Amylose 2, from Phenomenex) and the other a cellulose‐type one (Lux Cellulose‐4, ...from Phenomenex), were successfully used for the chiral resolution of three helical chromenes featuring a helicene‐like structure. The compound bearing a phenyl substituent on the helicene‐like structure was enantioresolved at 25°C with Lux Cellulose‐4 and a n‐hexane/1‐propanol 99:1 v/v eluent. With a n‐hexane/2‐propanol 99.8:0.2 v/v mobile phase, the same column (operated at 35°C) provided the separation of the four isomers of the compound having a hexyl residue on the helicene‐like motif and an additional asymmetric carbon. Lux Amylose‐2 was necessary for the enantioseparation of the compound having the sole hexyl residue on the helical scaffold. For the last compound a n‐hexane/2‐propanol 99.8:0.2 v/v eluent was used, and the column temperature was fixed at 5°C. The enantiomer elution order was appraised by using electronic circular dichroism and theoretical calculations. Notably, different thermodynamics of retention and enantioseparation were observed for molecules with pronounced structural similarity, that is, the enantiomer pairs of the compound containing the additional asymmetric carbon atom. Indeed, both entropically and enthalpically controlled adsorption and separation processes were observed.
We present an unusual upconversion process based on the sensitized tripletatriplet annihilation where the triplet energy of the donor exceeds that of the acceptor. Either a palladium ...octaethyl-porphyrin (PdOEP) or a platinum octaethyl-porphyrin (PtOEP) are the sensitizers, whereas tetraphenyl-pyrene (TPPy) is the emitter. The two couples convert the green to violet light in deoxygenated toluene with different efficiencies. The quantum yields of the upconversion processes (IBBUC) were calculated at different concentrations and intensities. We focused on low power non-coherent irradiation to simulate the solar energy supply. To demonstrate the important role played by the rate of the energy transfer from sensitizer to emitter in optimizing IBBUC, we tested the effect of the substitution of TPPy with 9,10-diphenylanthracene.
HBDI-like chromophores represent a novel set of biomimetic switches mimicking the fluophore of the green fluorescent protein that are currently studied with the hope to expand the molecular ...switch/motor toolbox. However, until now members capable of absorbing visible light in their neutral (i.e. non-anionic) form have not been reported. In this contribution we report the preparation of a HBDI-like chromophore based on a 3-phenyl benzofulvene scaffold capable to absorb blue light and photoisomerize in the picosecond time scale. More specifically, we show that double bond photoisomerization occurs in both the E-to-Z and Z-to-E directions and that these can be controlled by irradiating with blue-light and UV light respectively. Finally, as a preliminary applicative result, we report the incorporation of the chromophore in an amphiphilic molecule and demonstrate the formation of a visible light-sensitive nanoaggregated state in water.
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