Category Archives: ChemPhotoChem

Green Emission of Erbium Doped SYW Phosphors for Optical Thermometry And Solid‐State Lighting

Posted on 26 January 2024 by nSheetal Kumari, nA. S. Rao, nR. K. Sinhan

Graphical abstract showing the photoluminescence studies (emission spectra) of Er³⁺ doped SYW phosphors. The emission spectra recorded under the 380 nm excitation wavelength in the range 500–700 nm

Abstract

A series of Er³⁺ ions doped Sr₉Y₂W₄O₂₄ (SYW) phosphors have been synthesised using solid-state reaction technique. For optical thermometry and solid state lighting applications, the crystal structure, morphological, and luminescence features of the SYW : Er³⁺ phosphors were explored. X-ray diffraction (XRD) reveal that synthesized phosphors having single phase with a tetragonal crystal structure and I4₁/a space group. Scanning electron microscopy (SEM) was used to examine the morphological behaviour and presence of composition elements. The optical bandgap of the phosphor was evaluated using UV-Vis diffuse reflection spectra (DRS). The photoluminescence (PL) emission spectra were captured under 380 nm excitation, and the peak with the maximum intensity was identified at 563 nm ascribed to transition ⁴S_3/2→⁴I_15/2, that emits green color in visible region. The temperature dependent PL (TD-PL) spectra show that SYW phosphor is substantially more thermally stable, having thermal activation energy of about 0.247 eV. Additionally, the fluorescence intensity ratio (FIR) was used to study the optical sensing characteristics of the thermal quenching transitions (²H_11/2, ⁴S_3/2) with maximum relative sensitivity (S_R) and an absolute sensitivity (S_A) being 1.33 % K⁻¹and 0.307 % K⁻¹, respectively. All of the aforementioned findings demonstrate that SYW : Er³⁺ ions doped phosphors have potential for optical thermometry and other photonic devices.

Circularly Polarized Luminescence Switching of Chiral Perylene Diimide‐Doped Nematic Liquid Crystal Using DC Electric Field

Posted on 25 January 2024 by

Chiral luminescent nematic liquid crystals emit strong CPL signals and act as a reversible CPL switch regulated by turning the applied DC electric field on and off.

Abstract

To obtain chiral luminescent nematic liquid crystals (N*-LCs), two sets of chiral perylene luminescent materials (R,R)/(S,S)-N,N′-bis(1-cyclohexylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)/(S,S)-CPDI] and (R,R)/(S,S)-N,N′-bis(1-phenylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)/(S,S)-BPP] were prepared and doped into a nematic liquid crystal (N-LC), 5CB. The obtained liquid crystals N*-LC-CPDI and N*-LC-BPP emitted stronger circularly polarized luminescence (CPL) signals than the CPDI- and BPP-containing chiral poly(methyl methacrylate) (PMMA) luminescent films owing to higher helical twist power. When a direct current (DC) electric field was applied to N*-LC, a reversible CPL response was obtained due to the field-induced phase transition from the chiral nematic phase to the nematic phase. This demonstrated the successful construction of an ′′on-off-on′′ CPL system based on a DC electric field and was attributed to the change in the liquid crystalline organization from a uniformly lying helical structure to a planar one. This work can provide an effective strategy for the development of functional CPL devices in which the CPL can be regulated by applying a DC electric field to the N*-LC.

Slowing Hot Electron Cooling in CdSe Quantum Dots Using Electron‐Rich Exciton‐Delocalizing Ligands

Posted on 25 January 2024 by

Ordinarily, hot electrons cool within a few hundred femtoseconds in CdSe. However, chemical treatment of CdSe with the electron-rich MeOPTC generates hole-ligand interfacial states which disrupt the hot electrons’ cooling process, preventing a fraction of them from cooling efficiently.

Abstract

Understanding hot carrier dynamics in semiconductor nanocrystals is an important research focus due to their applications in photonics and photovoltaic devices. In this report, we investigated the effects of surface-bound exciton-delocalizing ligands (EDLs) on the lifetimes of hot electrons in CdSe quantum dots (QDs). After treatment of CdSe with two different phenylithiocarbamates (PTCs), a class of EDLs, the depletion times of the band-edge exciton bleach were roughly equivalent as observed through ultrafast transient absorption spectroscopy. However, following the initial ultrafast depletion, the PTC-treated samples continued to deplete while the untreated CdSe began recovering. Inspection of other transient features – such as the 3^rd exciton and hot biexciton – reveal a general trend in which the PTC-treated samples relax more slowly at short times (<10 ps) when compared with the untreated CdSe. At longer delay times, in the range of nanoseconds, the CdSe+CF₃OPTC loses nearly 80 % of its excited state populations, while the CdSe+MeOPTC loses only 20–40 %. We discuss the role that exciton delocalization plays in determining these observed rates as well as how they compare to previous studies. Kinetic differences between the two ligands are attributed to their electron donating/withdrawing abilities and coupling to the CdSe QD. Coherent vibrational wavepacket analysis supports this line of reasoning, showing increased coupling between the exciton and the longitudinal optical (LO) phonon due to increased Coulombic field strength around the hole and electron-donating MeOPTC. These results indicate that electron-rich PTCs are especially good candidates for use in QD devices that would make use of hot carriers.

Photocatalytic metal‐free oxidation of alcohols with molecular oxygen in supercritical CO2 medium

Posted on 25 January 2024 by

2-Fluoroanthraquinone has been identified as a non-toxic and accessible organic photocatalyst for green oxidation of alcohols to carbonyls in supercritical (sc) CO₂. Tuning of scCO₂ medium near the critical point allowed attaining high conversions (90–99 %). Molecular oxygen and air were used as safe and atom efficient oxidants. A plausible Hydrogen Atom Transfer (HAT) mechanism of the catalytic photooxidation process has been proposed.

Abstract

Near-UV-light-induced oxidative conversion of cyclic and linear alcohols into corresponding carbonyl compounds was achieved in the supercritical CO₂ medium under the action of molecular oxygen in the presence of 2-fluoroanthraquinone (1 mol %), a simple and available metal-free photocatalyst. A thorough examination of the impact of various process parameters on the reaction outcome allowed to identify a narrow density area at ~0.3 g/cm³ in the vicinity of the medium critical point and optimal reaction conditions (~45 °C, ~8.4 MPa) where up to 99 % conversions and 65–93 % yields of the oxidation products could be attained. Furthermore, it has been shown that compressed atmospheric air, a far cheaper and safer oxidizer than pure oxygen, can be applied to the reaction. Based on the experimental data, a plausible mechanism of the photocatalytic process has been proposed comprising photocatalyst excitation with near-UV light followed by the hydrogen atom transfer (HAT) as the key stages.

Unveiling the Ultrafast Electron Transfer Dynamics in Epitaxial Dodecahedron CsPbBr3/Au Heterostructure

Posted on 23 January 2024 by

Femtosecond transient absorption spectroscopy has been utilized to understand the charge transfer dynamics of CsPbBr₃/Au heterostructure. We find that distinct fast electron transfer in the CsPbBr₃/Au heterostructure, which is mainly ascribed to the strong epitaxial growth and strong electronic coupling between CsPbBr₃ and Au systems.

Abstract

Epitaxial perovskite heterostructures consisting noble metal nanoparticles have been received immense interest in hot carrier photovoltaic devices and photocatalysis. The major understanding of carrier extraction across the interface of perovskite heterostructure have shown exciting interest for next generation device applications. In the present study, dodecahedron CsPbBr₃/Au heterostructure was synthesized via hot injection method. From HR-TEM images, we observed direct epitaxial growth between (110) plane of CsPbBr₃ and (111) plane of Au nanoparticle (NPs), which was further supported by steady-state and time-resolved photoluminescence studies. Further, femtosecond transient absorption spectroscopy has been utilized to understand the charge transfer dynamics of synthesized samples. In CsPbBr₃/Au heterostructure, faster recovery has been noticed than that of pristine CsPbBr_3, which clearly suggests transfer of electrons from the conduction band of CsPbBr₃ to Au NPs. The distinct fast electron transfer in the CsPbBr₃/Au heterostructure can be mainly ascribed to the epitaxial growth and strong electronic coupling between CsPbBr₃ and Au NPs. The reduced bleach intensity, faster bleach growth and recovery kinetics strongly suggest efficient electron transfer from CsPbBr₃ NCs to Au NPs. These findings clearly establish that architecture of metal and perovskite heterostructures may pave way to develop suitable alternative for highly efficient photovoltaic devices and photocatalysis applications.

Effective light‐induced fluorescent H‐aggregation of fluorinated pyridyl‐azo dye via photoisomerization

Posted on 23 January 2024 by

An effective and efficient way was developed to convert monomer fluorinated pyridyl-azo dye to H-aggregated through UV-light induced trans-cis-trans photoisomerization.

Abstract

Here we present the synthesis of a new fluorinated pyridyl-azo dye and demonstrate an effective way to convert monomer fluorinated pyridyl-azo dye to H-aggregated form through UV-light induced trans-cis-trans photoisomerization. And upto a 12 : 88 ratio between monomer : aggregation was achieved through a small pulse of UV irradiation. The H-aggregation shows a unique high extinction co-efficient in UV-visible absorbance and unexpected fluorescence emission with a remarkably large Stokes shift. The solvent DMF and fluorine substituent were found to have a critical role in aggregation. ¹H, ¹⁹F NMR, and ¹⁹F-DOSY NMR experiments were used to confirm the aggregation and also confirm the absence of π-π stacking.

Synthesis of Piperidine‐based Derivatives as Red Emitting Lu‐minescent Materials

Posted on 23 January 2024 by nZhao Wang, nRanran Guo, nJunliang Wun

A novel piperidine-based red light material was efficiently constructed through a simple and mild reaction conditions. The color coordinates of 5 a (0.6978, 0.3020) and 5 af (0.6662, 0.3336) were near the standard red coordinates (0.67, 0.33) with extremely high color saturation (5 a: 99.97 %, 5 af: 100 %). Meanwhile, 5 a exhibits reversible redox processes, good electrochemical stability, and good whole transport performance, indicating that it could be potentially developed as red luminescent and hole-transporting material.

Abstract

Organic fluorescent materials have become increasingly attractive due to the requirements of green chemistry. In this study, the synthetic route of piperidine-based fluorescent materials was optimized with good to excellent yields. 37 fluorescent compounds were achieved with emission wavelength at 540–670 nm and chromogenic changed from green to standard red. The fluorescence quantum yields of 5 a, 5 ab, and 5 af were 1.96 %, 0.97 %, and 5.13 %, respectively. The relationship between the structure and luminescent properties has also been systematically discussed. This work presents the possibility of utilizing piperidine analogues to develop fluorescent probes in biological imaging, display devices and other related fields.

Near‐infrared Emissive Indolizine Squaraine Fluorophores as Strong Molecular Viscosity Sensors

Posted on 23 January 2024 by

A series of near-infrared absorbing and emitting indolizine squaraine fluorophores were designed and synthesized. The dyes were probed for their photophysical and electrochemical properties and observed to exhibit very high viscosity sensitivity.

Abstract

Changes in the viscosity of intracellular microenvironments may indicate the onset of diseases like diabetes, blood-based illnesses, hypertension, and Alzheimer's. To date, monitoring viscosity changes in the intracellular environment remains a challenge with prior work focusing primarily on visible light-absorbing viscosity sensing fluorophores. Herein, a series of near-infrared (NIR, 700–1000 nm) absorbing and emitting indolizine squaraine fluorophores (1PhSQ, 2PhSQ, SO₃SQ, 1DMASQ, 7DMASQ, and 1,7DMASQ) are synthesized and studied for NIR viscosity sensitivity. 2PhSQ exhibits a very high slope in its Forster-Hoffmann plot at 0.75 which indicates this dye is a potent viscosity sensor. The properties of the squaraine fluorophores are studied computationally via density functional theory (DFT) and time-dependent (TD)-DFT. Experimentally, both steady-state and time-resolved emission spectroscopy, absorption spectroscopy, and electrochemical characterization are conducted on the dyes. Precise photophysical tuning is observed within the series with emission maxima wavelengths as long as 881 nm for 1,7DMASQ and fluorescence quantum yields as high as 39.5 and 72.0 % for 1PhSQ in DCM and THF, respectively. The high tunability of this molecular scaffold renders indolizine squaraine fluorophores excellent prospects as viscosity-sensitive biological imaging agents with 2PhSQ giving a dramatically higher fluorescence quantum yield (from 0.3 to 37.1 %) as viscosity increases.

Tunable Phosphorescence in Metastable CuI Assemblies Prepared by Acid‐Fueled Crystal‐to‐Crystal Conversion

Posted on 23 January 2024 by

In this work, we report new metastable Cu^I assemblies prepared by crystal-to-crystal conversion that exhibit temperature-dependent phosphorescence complexity.

Abstract

Acid acts as a “fuel” in driving kinetic self-assembly, with crystals of the Cu^II complex ([Cu^IICl₂(BH)₂], BH=benzothiadiazole helicene derivative) being successfully converted to crystals of 1 ([H₂BH][CuBr₃]) and 2 ([H₂BH][CuBr₃⋅2H₂O]). The metastable features of 1 and 2 enable Cu^I guest release, with transformation into a thermodynamically favorable form 3 (H₂BH⋅2Br). Compound 1 exhibits dual phosphorescence at 452 nm (³MC) and 709 nm (³CT) at room temperature. At lower temperatures, the ³CT band disappears and the ³MC band weakens, while a new emission band at 621 nm (³ππ*) is enhanced. In 1, the subtle structural change and significant emission change depending on temperature is reversible. In contrast, 2 exhibits only ³MC emission at room temperature, with less efficient triplet-triplet energy transfer (TTET) below 250 K, and with residual ³ππ* emission occurring upon returning to room temperature, even after one week.

Abatement of volatile organic compounds employing a thermoplastic nano‐photocatalyst layered on a glass reactor

Posted on 22 January 2024 by

Volatile Organic Compounds (VOCs) represent a wide class of dangerous pollutants. Here, a new gas-flow photoreactor coated with a thermoplastic TiO₂-based nanocomposite is developed and used in the solar-triggered photocatalytic degradation of common VOCs. The peculiar design of the reactor combined with the features of the coating nanosystem provides a cheap and efficient way to boost the abatement of VOCs.

Abstract

Industrial development and urbanization have increased the emission of Volatile Organic Compounds (VOCs) into the atmosphere, causing environmental and health risks. Several approaches are used for their abatement, including chemical, thermo- and photo-catalytic oxidations, but they are not fully satisfactory. In this work, a thermoplastic TiO₂-based photo-catalyst was used as a coating layer of a glass-reactor. Solar-triggered photocatalytic degradation of ethanol, toluene, and acetone (used as model VOCs) highlights the better performance of the coated photoreactor than that of TiO₂ nanopowder. The influence of the pollutant flow rate on the photodegradation performance of the system was also investigated, revealing an inverse relationship between degradation and flow rates. The experimental data suggest that our approach provides a cost-effective and efficient way to boost the abatement of VOCs, useful for further industrial-scale applications. The morphology and the compositional homogeneity of the nanocomposite coating were addressed through Field Emission Scanning Electron Microscopy coupled with Energy Dispersive X-ray Analysis.