Photoinduced Emission Research Articles

Seeded Growth of Three-Dimensional Block Heterojunctions Featuring Photoinduced Emission Enhancement

Seeded Growth of Three-Dimensional Block Heterojunctions Featuring Photoinduced Emission Enhancement

Flexible and Dynamic Light-Guided Electrochemiluminescence for Spatiotemporal Imaging of Photoelectrochemical Processes on Hematite.

Here, we report an electrochemiluminescence (ECL)-based approach for imaging of local photoelectrochemical processes on hematite in a spatially and temporally controlled manner. The local processes were guided by flexible and dynamic light illumination, not requiring any prepatterned conductive features or photomasks, with a digital micromirror device (DMD). The imaging approach was based on light-addressable electrochemical reactions on hematite, resulting in photoinduced ECL emission for spatiotemporally resolved imaging of photoelectrochemical processes selectively guided by light illumination. After clarifying the capability of hematite as a photosensitive electrode, we validated that the illuminated hematite exhibited stable light-guided ECL emission in correspondence with the illuminated area, with a spatial resolution of 0.8 μm and a temporal resolution of 1 μs, even over a long period of 6 h. More importantly, this study exemplified the simple yet effective ECL-based approach for electrochemical visualization of local photoelectrochemical processes guided by flexible and dynamic adjustment of light illumination in a spatiotemporally controlled way.

Physico‐chemical Properties and Anticancer Activity of Carborane‐BODIPY Conjugates: A Review

AbstractCarboranes and BODIPYs are the well known boron containing compounds. Both are relatively easy to functionalize, and small modification in their structures allow turning of their spectroscopic properties readily suggest the importance of carborane‐BODIPY conjugates. The combination of boron rich carborane and photosensitizers activatable BODIPYs have potentials for adequate boron delivery to the cancer tissues for successful cancer therapy. This review covers the most recent development of carborane‐BODIPY conjugates in space electronic energy transfer, photoinduced electron transfer, fluorescence emission and AIE behaviors, and as promising BNCT agents. Given the high potential and flexibility of this carborane‐BODIPY conjugates, we believe that major developments are to be expected in the field of both material and medicinal science.

Satellite Red Emission from a Single Green-Emissive MnBr42- Tetrahedron in Soft Hybrid Single Crystals.

Photoinduced self-trapped exciton emission is common in soft matter metal halide semiconductors, whereas analogous phenomena in metal halide insulators with localized emitting centers and delayed satellite emission have rarely been identified. In this study, a new zero-dimensional Mn(II) hybrid of [3DPTPP]MnBr4 (3DPTPP = (3-(dimethylamino)propyl)(triphenyl)phosphonium) with only one crystallographic Mn2+ site but dual emission is reported. The delayed red emission (∼630 nm) is successfully assigned to a satellite of the green-emissive (∼530 nm) MnBr42- tetrahedron shifted by N-H vibration (∼2500 cm-1), directly evidenced by the Raman spectra and further supported by density functional theory calculation. The photoluminescence decay curves demonstrate their same origin, but the red emission exhibits a delayed process. The temperature- and pressure-dependent PL spectra, temperature-dependent distortion of the MnBr42- tetrahedron, and light polarization spectra confirmed the consistency and distinctness of the dual emission. This study will inspire further research on self-trapped optoelectronic processes in soft metal halides.

Achieving short-wavelength free radical emission by combining small conjugated structure and anti-Kasha emission

Since the natural narrow bandgaps of free radicals usually lead to emission in the long-wavelength region, it is still of great challenge to design radical luminescent materials with stable and short-wavelength emission in the ambient environment. In this work, a series of dicarbonyl-substituted organic molecules with small conjugated structures were used to form free radicals with short-wavelength radical emission. These low-conjugated molecules with only one benzene ring showed stable photoinduced free radical emission after doping with polymethyl methacrylate (PMMA) because the rigid polymer environment could help stabilize the free radicals and limit the non-radiative energy transfer. Moreover, PMMA with electron-withdrawing groups could promote the generation of carbonyl radical cations. The theoretical calculation suggests that the free radical with anti-Kasha emission derived from high energy excited state (D4 or D5) would directly relax to the ground state, combining with the small spin delocalization of the low conjugation free radical, leading to short-wavelength emission. More importantly, such free radical emissions could also respond to external stimulation such as light irradiation or heat treatment. These materials show great potential in lithography information recording and information encryption. This design strategy provides new insights into molecular and functional diversity of free radical materials.

Applications of Delayed Luminescence for tomato fruit quality assessment across varied Sicilian cultivation zones.

The food industry places significant emphasis on ensuring quality and traceability as key components of a healthy diet. To cater to consumer demands, researchers have prioritized the development of analytical techniques that can rapidly and non-invasively provide data on quality parameters. In this study, we propose to use the Delayed Luminescence (DL), an ultra-weak and photo-induced emission of optical photons, as a tool for a rapid evaluation of quality profile associated with fruit ripening, in support of traditional analysis methods. Delayed Luminescence measurements have been performed on cherry tomatoes, with and without the PGI "Pomodoro di Pachino" certification, harvested from two different growing areas of south-eastern Sicily (Italy). Then, DL emissions were correlated with soluble solid content and titratable acidity values, which are known to affect the flavor, the commerciality and the maturity degree of tomato fruits. In addition, we evaluated the changes in the DL parameters with respect to the geographical origin of the cherry tomatoes, with the aim of testing the possibility of applying the technique for identification purposes. The signals of Delayed Luminescence appeared to be good indicators of the macromolecular structure of the biological system, revealing structural changes related to the content of total soluble solids present in the juice of tomatoes analyzed, and they appeared unsuitable for authenticating vegetable crops, since the differences in the photon yields emitted by tomato Lots were not related to territory of origin. Thus, our results suggest that DL can be used as a nondestructive indicator of important parameters linked to tomato fruit quality.

Photo-Response with Radical Afterglow by Regulation of Spin Populations and Hole-Electron Distributions.

No matter photoinduced organic radicals have been reported frequently, they are usually non-luminescent at ambient conditions. The internal mechanism on stability and electronic transitions of photoinduced radicals, is thus crucial for the development of relevant materials. Herein, a series of photoinduced radical emission systems were developed conveniently through doping benzoic acids into the hydrogen donor polyvinyl alcohol (PVA) matrix. Visual photoinduced radical emission and photochromism could be observed on Ph-3COOH@PVA film with the formation of cyclohexadienyl-type structure. For the first time, radical afterglow appeared with energy transfer from triplet state. The appropriate introduction of carboxylic groups to three nonadjacent carbon atoms on the benzene ring was the best for decreasing spin population and promoting electronic transitions of the radical. This study largely expands the radical emission property from both internal mechanism and practical application.

Photo‐Response with Radical Afterglow by Regulation of Spin Populations and Hole‐Electron Distributions

AbstractNo matter photoinduced organic radicals have been reported frequently, they are usually non‐luminescent at ambient conditions. The internal mechanism on stability and electronic transitions of photoinduced radicals, is thus crucial for the development of relevant materials. Herein, a series of photoinduced radical emission systems were developed conveniently through doping benzoic acids into the hydrogen donor polyvinyl alcohol (PVA) matrix. Visual photoinduced radical emission and photochromism could be observed on Ph‐3COOH@PVA film with the formation of cyclohexadienyl‐type structure. For the first time, radical afterglow appeared with energy transfer from triplet state. The appropriate introduction of carboxylic groups to three nonadjacent carbon atoms on the benzene ring was the best for decreasing spin population and promoting electronic transitions of the radical. This study largely expands the radical emission property from both internal mechanism and practical application.

Photo-induced Electron Emission of Nanostructured Carbon Thin Film Based Transmission Photocathodes at Different Electric Field

Very thin nanostructured carbon films were deposited on quartz substrate by reactive magnetron sputtering using graphite target and gas mixture of Ar and reactive gas N_2 or N_2+H_2. Film thicknesses were in the range of 20-25 nm. Rutherford backscattering spectrometry and Elastic recoil detection analytical method determined the concentration of elements in the films. Scanning electron microscopy scanned the surface morphology of carbon films. Raman spectroscopy was used for chemical structural properties determination of very thin carbon films. Raman spectra intensities were fitted with Gaussian peaks. The photo-induced (pulsed laser - 266 nm) electron emission properties of very thin nanostructured carbon films were investigated by the measurement of cathode bunch charge at different electric field and calculate quantum efficiency. The influence of different electric field on the photo-induced electron emission characteristics of prepared transmission photocathodes are discussed.

Disentangling surface atomic motions from surface field effects in ultrafast low-energy electron diffraction

Ultrafast low-energy electron diffraction holds potential to provide atomic level details to the surface dynamics controlling processes from surface chemistry to exotic collective effects. Accessing the primary timescales requires subpicosecond excitation pulses to prepare the corresponding nonequilibrium state. The needed excitation for maximum contrast above background invariably leads to photoinduced electron emission with the creation of surface fields that affect diffraction and must be quantified to recover the key structural dynamics. Using 2 keV ultrashort low-energy electron bunches, we investigate this field effect on the ensuing electron distribution in projection imaging and diffraction as a function of excitation intensity. Using a structural model, we demonstrate a quantitative separation of the surface field effect on electron diffraction, enabling isolation of the structural dynamics of interest. Particle trajectory simulations provide insight into the correlation between geometrical characteristics of the charge separated region and the corresponding intensity modulation at the detector.

Balancing the interplay between ligand ejection and therapeutic window light absorption in ruthenium polypyridyl complexes.

Ruthenium polypyridyl complexes have gained significant interest as photochemotherapies (PCTs) where their excited-state properties play a critical role in the photo-cytotoxicity mechanism and efficacy. Herein we report a systematic electrochemical, spectrochemical, and photophysical analysis of a series of ruthenium(II) polypyridyl complexes of the type [Ru(bpy)2(N-N)]2+ (where bpy = 2,2'-bipyridine; N-N is a bidentate polypyridyl ligand) designed to mimic PCTs. In this series, the N-N ligand was modified through increased conjugation and/or incorporation of electronegative heteroatoms to shift the metal-to-ligand charge-transfer (MLCT) absorptions near the therapeutic window for PCTs (600-1100 nm) while incorporating steric bulk to trigger photoinduced ligand dissociation. The lowest energy MLCT absorptions were red-shifted from λmax = 454 nm to 564 nm, with emission energies decreasing from λmax = 620 nm to 850 nm. Photoinduced ligand ejection and temperature-dependent emission studies revealed an important interplay between red-shifting MLCT absorptions and accessing the dissociative 3dd* states, with energy barriers between the 3MLCT* and 3dd* states ranging from 850 cm-1 to 2580 cm-1 for the complexes measured. This work demonstrates the importance of understanding both the MLCT manifold and 3dd* state energy levels in the future design of ligands and complexes for PCT.

Photoinduced Radical Emission in a Coassembly System

AbstractDeveloping radical emission at ambient conditions is a challenging task since radical species are unstable in air. In the present work, we overcome this challenge by coassembling a series of tricarbonyl‐substituted benzene molecules with polyvinyl alcohol (PVA). The strong hydrogen bonds between the guest dopants and the PVA host matrix protect the free radicals of carbonyl compounds after light irradiation, leading to strong solid state free radical emission. Changing temperature and peripheral functional groups of the tricarbonyl‐substituted benzenes can influence the intensity of the radical emission. Quantum‐chemical calculations predict that such free radical fluorescence originates from anti‐Kasha D2→D0vertical emission by the anion radicals. The photoinduced radical emission by the tricarbonyl‐substituted benzenes was successfully utilized for information encryption application.

Photoinduced Radical Emission in a Coassembly System

Developing radical emission at ambient conditions is a challenging task since radical species are unstable in air. In the present work, we overcome this challenge by coassembling a series of tricarbonyl-substituted benzene molecules with polyvinyl alcohol (PVA). The strong hydrogen bonds between the guest dopants and the PVA host matrix protect the free radicals of carbonyl compounds after light irradiation, leading to strong solid state free radical emission. Changing temperature and peripheral functional groups of the tricarbonyl-substituted benzenes can influence the intensity of the radical emission. Quantum-chemical calculations predict that such free radical fluorescence originates from anti-Kasha D2 →D0 vertical emission by the anion radicals. The photoinduced radical emission by the tricarbonyl-substituted benzenes was successfully utilized for information encryption application.

Modeling of Laser-Induced Plasmon Effects in GNS-DLC-Based Material for Application in X-ray Source Array Sensors.

An important direction in the development of X-ray computed tomography sensors in systems with increased scanning speed and spatial resolution is the creation of an array of miniature current sources. In this paper, we describe a new material based on gold nanostars (GNS) embedded in nanoscale diamond-like carbon (DLC) films (thickness of 20 nm) for constructing a pixel current source with photoinduced electron emission. The effect of localized surface plasmon resonance in GNS on optical properties in the wavelength range from UV to near IR, peculiarities of localization of field and thermal sources, generation of high-energy hot electrons, and mechanisms of their transportation in vacuum are investigated. The advantages of the proposed material and the prospects for using X-ray computed tomography in the matrix source are evaluated.

A Highly Ordered Quantum Dot Supramolecular Assembly Exhibiting Photoinduced Emission Enhancement

AbstractMulticomponent supramolecular assembly systems enable the generation of materials with outstanding properties, not obtained from single‐component systems, via a synergetic effect. Herein, we demonstrate a novel supramolecular coassembly system rendering highly ordered quantum dot (QD) arrangement structures formed via the self‐assembly of azobenzene derivatives, where the photocontrollable photoluminescence (PL) properties of the QDs are realized based on photoisomerization. Upon mixing the assembled azobenzene derivatives and QDs in apolar media, a time‐evolution coaggregation into hierarchical nanosheets with a highly ordered QD arrangement structure occurs. Upon photoirradiation, the nanosheets transform into ill‐defined aggregates without arranged QDs together with enhancing the PL intensity. In days, the photoirradiated coaggregates undergo recovery of the PL properties corresponding to the arranged QDs through thermal isomerization.

A Highly Ordered Quantum Dot Supramolecular Assembly Exhibiting Photoinduced Emission Enhancement.

Multicomponent supramolecular assembly systems enable the generation of materials with outstanding properties, not obtained from single-component systems, via a synergetic effect. Herein, we demonstrate a novel supramolecular coassembly system rendering highly ordered quantum dot (QD) arrangement structures formed via the self-assembly of azobenzene derivatives, where the photocontrollable photoluminescence (PL) properties of the QDs are realized based on photoisomerization. Upon mixing the assembled azobenzene derivatives and QDs in apolar media, a time-evolution coaggregation into hierarchical nanosheets with a highly ordered QD arrangement structure occurs. Upon photoirradiation, the nanosheets transform into ill-defined aggregates without arranged QDs together with enhancing the PL intensity. In days, the photoirradiated coaggregates undergo recovery of the PL properties corresponding to the arranged QDs through thermal isomerization.

AIE Ligand Constructed Zn(II) Complex with Reversible Photo-induced Color and Emission Changes

Fluoran salicylaldehyde hydrazone metal complex(FSHMC) is a kind of recently reported photo-responsive system, which has the advantages of simple synthesis, multiple colors as well as distinct color change before and after UV light irradiation. However, the emission property of FSHMC is relatively unitary. In solid state, especially, only fluorescence quench is induced after UV light irradiation, which limits their applications. In this work, a typical aggregation-induced emission(AIE) moiety of tetraphenylethene(TPE) was introduced to the design of FSHMC. The obtained FSHMC, 2-Zn, exhibited reversible color and fluorescence changes upon UV light irradiation. Due to the AIE feature of compound 2, 2-Zn exhibited different emission changes upon UV light irradiation in THF and in solid matrix, because of the fluorescence resonance energy transfer(FRET) process from TPE moiety to rhodamine B moiety.

Thermally activated processes in an organic long-persistent luminescence system.

Glow-in-the-dark materials can store absorbed photon energy and emit light for long periods of time. While inorganic long-persistent luminescence (LPL) materials are crystalline and often require rare metals, organic LPL (OLPL) materials are flexible and require no rare metals. The emission process of OLPL systems consists of photoinduced charge separation, charge accumulation, and emission from charge recombination. Although emission processes of OLPL systems have been investigated, the charge separation and accumulation processes remain enigmatic. In this study, we investigated the charge carrier dynamics of a binary OLPL system comprising of electron donors and acceptors. We confirmed the presence of thermal activation processes, thermally activated delayed fluorescence and thermoluminescence in the OLPL system.

Tumor tissues diagnosis with PIEE lipid droplet vesicles

A molecule ANB (6-(4-aminostyryl)-1,3-dioxo-1H-benzo[de]isoquinolin -2(3 H)-yl)-n-butane), was developed for fluorescence turn-on imaging of cancer cells lipid droplets (LDs). ANB exercised synergistically aggregation induced emission enhancement and photochromism, which are essential to construct a photoinduced emission enhancement (PIEE) LDs. The fluorescent nanostructures PIEE-LDs extremely improve intracellular imaging contrast with high emission intensity, high emission contrast to cytosol and high photostability. Following these unique optical properties, we statistically analyzed the differences of LDs between cancer and normal cells as well as successfully observed LDs progression and fusion in living cells over a long period. Consequently, the xenograft tumor tissues were favorably distinguished from normal based on this superior PIEE-LDs. It is known that ANB exhibited excited-state conformational conversion between the twist intramolecular charge transfer (TICT) and local excited (LE) states. Based on the results of our studies, we found that LE state became dominate and presented aggregation induced emission enhancement when ANB stay in LDs, which allows us to build a fluorescent nanovesicle model to explain the distinct fluorescence imaging of ANB in LDs. Furthermore, photochromism occurred when irradiation that could promoted emission behavior of bright nanovesicles LDs to further level, and achieve PIEE-LDs.

Modulation of physical properties of organic cocrystals by amino acid chirality

Amino acid chirality plays an important role in conveying directionality and specificity to their supramolecular organization. However, the impact of enantiopure and racemic amino acids on the favorable packing and macroscopic properties of organic cocrystals with nonchiral coformers is poorly understood. Herein, we performed a systematic study of the effect of chirality on the macroscopic properties of acetylated alanine (AcA) single crystals and cocrystals with a nonchiral photo-sensitive bipyridine derivative (BPE). Cocrystallization with BPE produced a marked morphology transition that improved the supramolecular chirality, thermal stability and mechanical strength of AcA crystals. The distinct supramolecular packing modes were analyzed by X-ray crystallography. The highest rigidity was observed for BPE/dl-AcA, while BPE/d-AcA and BPE/l-AcA crystals exhibited higher efficiency of photo-induced emission for fluorescent imprinting, as well as significantly higher piezoelectricity. This work provides a striking illustration that subtle differences in amino acid stereochemistry translate into tunable macroscopic properties of organic cocrystals for future applications in rigid solids, fluorescent imprinting, and energy harvesting.