ChemPhotoChem最新文献

To enhance organic light emitting diode (OLED) performance, host materials with high triplet energies are crucial for confining excitons, despite increasing driving voltages due to the singlet-triplet energy gap. We synthesized sulfonylbis(4,1-phenylene)bis(3,6-disubstituted-9H-carbazole) derivatives as donor-acceptor-donor host materials, namely compounds 3, 5 and 7, with varying fluorination levels. These compounds show moderate singlet-triplet energy splitting and molecular dipole moments, allowing for fine-tuning of hole-transport mobilities, deeper frontier orbital energies, and a red shift in singlet emission while maintaining high triplet energy levels. These adjustments impact a range of physical, electronic and optical properties. The materials exhibit exceptional thermal stability, with decomposition starting above 400 °C and glass transition temperatures over 130 °C. Used with the green TADF emitter DACT-II, these hosts enable reverse intersystem crossing rates between 7.43×10⁴ s⁻¹ and 1.77×10⁵ s⁻¹. While OLEDs using mCP as a reference host achieve a maximum quantum efficiency of 18.5 %, those with host 5 show lower efficiency roll-off, leading to higher external quantum efficiency at brightness levels above 2000 cd/m² without colour shift. The reduced roll-off in devices with host 5 compared to mCP is attributed to effective Förster and Dexter energy transfers to DACT-II at high currents, enhancing light emission pathways.

In recent years, parahydrogen-induced hyperpolarization has become a focus for future medical applications. Similar to the established dynamic nuclear polarization method, a biocompatible bolus from a hyperpolarized sample can be produced for in vivo studies. However, this requires removing toxic hydrogenation catalysts, which inevitably must be used. Additionally, the ratio between the substrate to be hyperpolarized (e. g. pyruvate) and a mandatory catalyst must also be maintained. Even the smallest differences can lead to a reduction in generated signal amplification. In particular, weighing small amounts of catalysts leads to inaccuracies in sample preparations. Fluorescence spectroscopy provides a rapid and sensitive enough approach to determine catalyst concentration. The Ir-IMes metal complexes used in SABRE lead to a quenching of the fluorescence of the solvent, dependent on its concentration. This can be used to quickly estimate the actual concentration in a solution with very small quantities of catalysts. Hence, fluorescence spectroscopy offers a rapid and reliable quality control method for the preparation of samples to be hyperpolarized. In addition, it can also be used as a quality control method to assess filtration efficacy before administration of hyperpolarized samples.

Herein, we have designed aqueous dispersed self-assembled nanostructures with diverse morphologies from the zinc tetraphenyl porphyrin (ZnTPP) monomer employing simple solution-based coprecipitation methods. Detailed morphological studies have been carried out by various electron microscopy techniques. Finally, the structural features were correlated with the underpinning photophysical processes using steady-state and time-resolved spectroscopy. Detailed studies suggest that controlled morphology and highly defined intermolecular interactions affect the overall photoinduced charge transfer process. Based on the fundamental investigations, all these different types of nanostructures have been utilized as photocatalysts for solar hydrogen production without using any cocatalysts, and it was found that the spherical nanostructure exhibits significantly higher H₂ production rates of ∼1682 μ mole/g, which is a few folds higher than other 1D and 2D nanostructured materials. The experimental findings were further supported by the TD-DFT study. Furthermore, the detailed computational studies suggest that the spherical aggregates exhibited a more vital interaction between the ZnTPP molecules, causing significant electronic coupling between bright local excited and charge transfer states, which supports our experimental findings. Finally, we have selectively utilized the oxidative half-reaction for the simultaneous transformation of glycerol to valuable chemicals along with photocatalytic H₂ production through reductive half-reaction.

We have designed and synthesized a novel series of cyanostilbene-based amorphous molecular materials with different methylene chain lengths, BMAC-n (n=3,4,5,6), and investigated their emitting properties in solution and various solid states. All BMAC-n molecules showed solvatochromic fluorescence in solutions. Emission spectra of BMAC-n molecules in the same solution were identical to one another irrespective of the methylene chain length while the spectra in crystalline states depended on their methylene chain length. As in solutions, emission spectra of their spin-coated amorphous films were identical to each other irrespective of the methylene chain length. Emission spectra of rubbed amorphous films prepared by grinding their crystals were identical to those for spin-coated amorphous films; however, comparative studies between spin-coated and rubbed amorphous films indicated that fluorescence quantum yields and photochemical reactivity depend on the preparation method.

The ongoing search for innovative and environmentally friendly luminescent materials coupled with customizable physical and chemical properties at the nanoscale positions carbon dots (CDots) as ideal candidates for photonic applications. However, even today, their rational design for specific applications remains elusive due to the unknown relationship between optical and structural properties. Therefore, this study aims to fill this gap by linking the chemical structure of the precursor and synthetic conditions to the final structural composition of the CDots and, by extension, to their optical properties. The study shows that while CDots are chemically stable, their optical properties, which are determined by the carbonaceous core and surface groups, are highly pH dependent. These properties, together with the long fluorescence lifetimes observed in living cells (>10 ns), make these biomass-derived CDots promising probes for time-resolved fluorescence imaging.

2-(3,6-Bis(4-methoxyphenyl)-2,2,5,5-tetramethyl-4-oxo-4,5-dihydropentalen-1(2H)-ylidene)malononitrile (DPM-An) and 2,2′-(3,6-bis(4-methoxyphenyl)-2,2,5,5-tetramethyl-2,5-dihydropentalene-1,4-diylidene)dimalononitrile (DPD-An), both bearing the 2,5-dihydropentalene core and intramolecular electron donor–acceptor moieties, were prepared and subjected to photophysical studies. The absorption spectra of DPM-An and DPD-An in CH₂Cl₂ at room temperature contain maxima at similar wavelengths of 406 and 409 nm, respectively. These substances do not luminesce in CH₂Cl₂ solution at room temperature, but they do emit light when present in poly(methyl methacrylate) films. Interestingly, DPM-An and DPD-An in the film forms display nearly identical emission (EM) spectra with respective maxima at 592 and 594 nm. In contrast, DPD-An has a longer EM lifetime than does DPM-An. Therefore, the dihydropentalene derivatives, exemplified by DPM-An and DPD-An, may be a family of substances in which excited state decay rate can be varied without changing EM wavelengths.

The use of organic molecules as photosensitizers in photoredox catalysis is an attractive research field as it has the potential to replace conventionally used photosensitizers, which are based on rare metals. In the context of light-driven hydrogen evolution catalysis, the radical formation of two perylene monoimide dyes (PMIs) was studied by means of electron paramagnetic resonance (EPR) and UV/Vis spectroscopy. The PMIs were reduced and oxidized both photochemically and electrochemically to study the changes in absorption and EPR signature. A distinct differentiation between the two PMIs as well as a comparison between the oxidative and reductive processes can be made by EPR measurements. UV/Vis measurements showed different features under redox conditions. This study addresses a gap in understanding the radical intermediate formation during photocatalytic processes.

Herein, we report the synthesis of new near-infrared (NIR) fluorescent dyes based on the pyridinium−cyclic enolate betaine (PCB) skeleton. The formation of the electron-donor−π−electron-acceptor (D−π−A) type dye with the electron-donating N,N-diphenyl amino group and the electron-accepting PCB skeleton through a series of π−spacers allowed us to achieve NIR fluorescence. Particularly, a dye with a thienylisothianaphthene spacer showed NIR fluorescence with a significant intensity (λ_PL=822 nm, Φ_PL=0.19 in DMSO). Detailed experimental and theoretical analyses suggested that the structural relaxation to a planar quinoidal form in the S₁ state would be critical for intense NIR fluorescence.

Room temperature afterglow materials have received widespread attention and application in anti-counterfeiting, imaging, and other fields, but the many shortcomings of traditional afterglow materials in terms of cost, environment, and synthesis methods have limited their development. In contrast, carbon dot materials have attracted more and more research due to their numerous advantages and great potential for development. However, the preparation of carbon dot materials with phosphorescence and delayed fluorescence afterglow emission capabilities remains a difficult task. In this study, a series of long life afterglow carbon dot composites with single-mode and dual-mode afterglow emission were successfully prepared by inserting carbon dots synthesized from glucose and glycine into boric acid matrix through a two-step hydrothermal method. This series of carbon dot composites has achieved a transformation from single-mode phosphorescent emission to unique dual-mode afterglow emission, allowing for efficient environmental response color modulation. The composites display different afterglow emissions dominated by either phosphorescent or delayed fluorescence at different temperatures. Based on their excellent temperature sensitivity, a single-mode long phosphorescence with a lifetime of 1.62 seconds was achieved at low temperature. In summary, we have discovered a convenient and efficient method to achieve dual-mode emission by adjusting the matrix proportion.

A systematic investigation of the photoinduced [6π]-electrocyclization reaction of diphenylamine and N-methyldiphenylamine has been carried out under steady-state and time-resolved conditions in homogeneous (cyclohexane, acetonitrile and methanol) and micellar solutions (sodium dodecyl sulfate -SDS, cetyltrimethylammonium chloride-CTAC and polyethylene glycol monododecyl ether-Brij P35). The photolysis of such compounds in both homogeneous and micro-heterogeneous media afforded the corresponding carbazoles in almost quantitative yield under oxidative conditions. Furthermore, the relative rate of formation of the photoproducts increases when moving from homogeneous media to micellar solution, due to the environmental confined and hydrophobic micellar core as highlighted by 1D and 2D NMR (NOESY and DOSY) spectroscopic analyses.