Photoinduced Behavior Research Articles

Photoinduced electron transfer from carbon nanotubes to fullerenes: C60versus C70.

Hybrid carbon materials are found to exhibit novel optoelectronic properties at their interfaces, but the related interfacial carrier dynamics is rarely explored theoretically. In this contribution, we have employed density functional theory (DFT) and DFT-based nonadiabatic dynamics methods to explore photoinduced interfacial electron transfer processes at interfaces between a single-walled carbon nanotube with chiral index (6,5) and C60 or C70 (C60@CNT65 and C70@CNT65). We have found that with low E11 excitation, electron transfer takes place from CNT65 to C60 and C70 in both heterojunctions. This process is ultrafast and completed within about 200 fs, which is consistent with recent experiments. Differently, high E22 excitation does not induce electron injection to C60 in C60@CNT65; instead, "hot" electrons produced within CNT65 will be trapped in its higher conduction band for a while because of slow inter-band relaxation. By contrast, in C70@CNT65, high E22 excitation still can lead to ultrafast electron transfer to C70, but only a comparable amount of electrons are transferred (ca. 30%). Interestingly, electrons either remaining on CNT65 or transferred to C70 are trapped in the higher conduction band for a while, similarly, due to slow inter-band relaxation. The present results could be useful to guide the design of excellent interfaces of mixed-dimensional hybrid carbon materials for various optoelectronic applications.

Time-resolved emission microscopy of light-induced aggregation of luminescent polymers

Photon pressure has been used to induce the aggregation from solution of a series of photoluminescent conjugated polyelectrolytes containing tetraphenylethene units. These polymers show steady-state and time-resolved emission properties that are dependent on the local chromophore environment that can be influenced by the degree of intra- and inter-molecular interactions, which enables the photoaggregation process to be monitored by time-resolved fluorescence imaging techniques. Structural differences in the polymer lead to variations in the photo-induced aggregation behaviour.

Unique Layer-Doping-Induced Regulation of Charge Behavior in Metal-Free Carbon Nitride Photoanodes for Enhanced Performance.

Photoinduced charge carrier behavior is critical in determining photoelectrocatalytic activity. In this study, a unique layer-doped metal-free polymeric carbon nitride (C3 N4 ) photoanode is fabricated by using one-pot thermal vapor deposition. With this method, a photoanode consisting of a phosphorus-doped top layer, boron-doped middle layer, and pristine C3 N4 bottom layer, was formed as a result of the difference in thermal polymerization kinetics associated with the boron-containing H3 BO3 -melamine complex and the phosphorus-containing H3 PO4 -dicyandiamide complex. This layer-doping fabrication strategy effectively contributes to the formation of dual junctions that optimizing charge carrier behavior. The ternary-layer C3 N4 photoanode exhibits significantly enhanced photoelectrochemical water oxidation activity compared to pristine C3 N4 , with a record photocurrent density of 150±10 μA cm-2 at 1.23 V vs. RHE. This layer-doping strategy provides an effective means for design and fabrication of photoelectrodes for solar water oxidation.

Photo-induced instability behaviors of IGZO TFTs caused by the reversible charge trapping

Photo-induced instability behaviors of IGZO TFTs caused by the reversible charge trapping

Photo-induced instability behaviors of IGZO TFTs caused by the reversible charge trapping

Photo-induced instability behaviors of IGZO TFTs caused by the reversible charge trapping

Phototautomerism of triazolo-triazole scaffold

Abstract It is shown that 4-methyl-7-(4-hydroxyphenyl)-[1,2,4]-triazolo[3,2-c][1,2,4]triazole exhibits a rich photoinduced protolytic behavior: Forster cycle shows that the protonated nitrogen of the triazolo-triazole ring is a weak photoacid, with Δ pKa ≈ − 3 ; furthermore, at moderately basic pH its deprotonated monoanion exhibits a long distance water mediated phototautomerism, in which the hydroxyl group releases a proton to solvent and a basic nitrogen of the triazolo-triazole fused ring, different from that protonated in the neutral species, is protonated by the solvent.

Photosensitive Supramolecular Micelles with Complementary Hydrogen Bonding Motifs To Improve the Efficacy of Cancer Chemotherapy.

Photosensitive supramolecular micelles, a combination of intermolecular hydrogen bonds between complementary adenine (A) and uracil (U) groups and a blend of two types of supramolecular polymers, can stably self-assemble into structurally stable, spherical micelles in aqueous solution before and after photoirradiation. The resulting micelles possess unique amphiphilic properties, photo-induced tunable phase-transition behavior, excellent biocompatibility, well-controlled spherical morphology, and can be tailored in size. Moreover, the drug content and entrapment efficiency can be finely tuned, and release kinetics can be modulated using combinations of changes in temperature and photoirradiation, making these micelles highly addictive as drug nanocarriers. Importantly, cytotoxicity assays and flow cytometric analyses confirmed that drug-loaded irradiated micelles exerted more potent cytotoxic effects against cancer cells and exhibited much higher cellular uptake efficiency than the free drug and drug-loaded nonirradiated micelles, indicating that the drug-loaded irradiated micelles rapidly entered the tumor cells to induce massive cell death. Therefore, this newly-developed supramolecular system could serve as a safe, efficient nanocarrier to effectively inhibit the growth and spread of primary tumors.

Photo-induced bending behaviour of side-on linear liquid crystal polymers with high molecular weight

ABSTRACT Two photoresponsive side-on linear liquid crystal polymers (SLLCPs) with different spacer lengths have been synthesised through facile ring-opening metathesis polymerisation (ROMP). For the first time, high molecular weight SLLCPs with polynorbornene backbone and azobenzene side chains are obtained and processed into films by the melt shear-induced orientation method. These SLLCP films exhibit fast and large photo-induced bending behaviour, showing bend degree up to 72° in 3 s upon UV irradiation at ambient temperature. The shape of these films remains unchanged under visible light, demonstrating good shape stability against sunlight. Moreover, owing to their linear structure, the SLLCP films are recyclable through traditional melting or solution methods. Possessing these features, these SLLCP films show application prospects in the fields of light-controllable flexible actuators.

Influence of the First Chromophore-Forming Residue on Photobleaching and Oxidative Photoconversion of EGFP and EYFP.

Enhanced green fluorescent protein (EGFP)—one of the most widely applied genetically encoded fluorescent probes—carries the threonine-tyrosine-glycine (TYG) chromophore. EGFP efficiently undergoes green-to-red oxidative photoconversion (“redding”) with electron acceptors. Enhanced yellow fluorescent protein (EYFP), a close EGFP homologue (five amino acid substitutions), has a glycine-tyrosine-glycine (GYG) chromophore and is much less susceptible to redding, requiring halide ions in addition to the oxidants. In this contribution we aim to clarify the role of the first chromophore-forming amino acid in photoinduced behavior of these fluorescent proteins. To that end, we compared photobleaching and redding kinetics of EGFP, EYFP, and their mutants with reciprocally substituted chromophore residues, EGFP-T65G and EYFP-G65T. Measurements showed that T65G mutation significantly increases EGFP photostability and inhibits its excited-state oxidation efficiency. Remarkably, while EYFP-G65T demonstrated highly increased spectral sensitivity to chloride, it is also able to undergo redding chloride-independently. Atomistic calculations reveal that the GYG chromophore has an increased flexibility, which facilitates radiationless relaxation leading to the reduced fluorescence quantum yield in the T65G mutant. The GYG chromophore also has larger oscillator strength as compared to TYG, which leads to a shorter radiative lifetime (i.e., a faster rate of fluorescence). The faster fluorescence rate partially compensates for the loss of quantum efficiency due to radiationless relaxation. The shorter excited-state lifetime of the GYG chromophore is responsible for its increased photostability and resistance to redding. In EYFP and EYFP-G65T, the chromophore is stabilized by π-stacking with Tyr203, which suppresses its twisting motions relative to EGFP.

Ultrasonically sprayed-on perovskite solar cells-effects of organic cation on defect formation of CH3NH3PbI3 films

Methylammonium lead iodide (CH3NH3PbI3) based perovskite having low degrees of the disorder is of great interest for optoelectronic and photovoltaic applications. In this work, a layer of CH3NH3PbI3 was successfully prepared using an ultrasonically sprayed-nebulous method. Changes in structural and optical properties alongside with photo-induced charge separation and transportation behavior were systematically studied. The surface photovoltage spectra reveal a significant reduction of the density of deep defect states as the organic content was increased. It was observed that the measured values of Urbach energies decrease from 33.36 to 28.24 meV as the amount of organic content was increased to an optimum value. The best perovskite solar cells obtained using the sprayed-on approach exhibited a Jsc of 16.54 mA/cm2, a Voc of 0.99 V, and a FF of 62.4, resulting in an overall PCE of 10.09%.

Growth of CdSe/MoS2 vertical heterostructures for fast visible-wavelength photodetectors

Heterostructures composed of different semiconducting materials have aroused wide attentions due to their fascinating properties originated from the interfaces. Particularly, the recent two dimensional layered materials (2DLM) have provided novel platforms to flexibly design the heterostructures for diverse electronic and optoelectronic applications. In this work, we have reported the growth of CdSe nanoplates/MoS2 monolayer vertical heterostructures with efficient and fast visible-wavelength photodetections. Highly dense CdSe nanoplates were vertically assembled on monolayer MoS2 through a two-step chemical vapor deposition (CVD) process. The interfacial photoinduced charge behaviors were investigated in detail via the time resolution photoluminescence (TRPL) measurements, revealing the efficient charge transfer across the heterointerface. Benefiting from the large CdSe coverage and efficient charge transfer, superior photodetection performances of the CdSe/MoS2 heterostructures can be obtained with an enhanced photoresponsivity of 1.63 A/W, which can be further improved to be 12 A/W via applying the gate voltage. Besides, the heterostructure detectors also exhibit a very fast photoresponse speed of 370 μs, much faster than previous photodetectors based on CVD-grown 2D heterostructures. The as-synthesized CdSe/MoS2 heterostructures may find important applications in integrated optoelectronic systems.

Hydrothermal synthesis of nanoporous lead selenide thin films: photoelectrochemical and resistive switching memory applications

The interconnected nanoporous lead selenide (PbSe) thin films were synthesized with the aid of polyvinyl alcohol (PVA) as a surface directing agent by simple hydrothermal route. Films were deposited with different time intervals like 1, 2 and 3 h. Effect of time variation was studied by structural, morphological and optical characterizations. XRD analysis revealed that the film exhibit a cubic phase of PbSe. SEM study shows an evolution in nanoflakes like morphological feature. It is observed that, the nanoflakes become denser with an increase in the diameter of the platelets as the deposition time increases. Interconnected nanoporous network, forming well defined 3D nanoenvelopes has been developed to analyze solar cell and resistive switching properties. The photoelectrochemical (PEC) performance of nanoporous PbSe thin films was tested in Polysulfide electrolyte. Among all PbSe films, the sample prepared at 3 h shows higher PEC performance with maximum short circuit current 97 µA/cm2 and open circuit voltage 110 mV. In addition to this, Ag/PbSe/FTO thin film device shows the photo-induced resistive switching behavior. The non-volatile memory results suggested that the memory device is able to switch up to 104 cycles and store the data up to 103 s with good uniformity during the resistive switching process. The analysis of I–V results revealed that the Ohmic and space-charge-limited current are responsible for current conduction in the Ag/PbSe/FTO thin film memory device. The results of present investigation suggest that the nanoporous lead selenide thin films are potential candidate for the photoelectrochemical and resistive switching memory applications.

In Situ Spectrospecopy Investigation of the Surface-Interface Charge-Transfer Process over Tailored Nano-Structured Based PEC Fuel Cells for Solar Energy Harvesting and Conversions

Solar energy induced catalytic reactions allow solar energy to be used directly in sunlight-to-chemical energy conversions. Many scientific progress have been made in solar energy utilization and conversions, whereas, scientists from all over the world claimed that there are still many problems need to be further addressed including how to further enhance the solar energy utilization & conversion efficiency etc. The detail micro-interface process, redox mechanism, charge-carrier transfer behavior and active species actions need to be further studied. Following all of these concerns, series of multifunctional complex oxides with hetero-junctions have been well designed in our group towards solar energy utilization and conversion process via photo-induced chemical process, and different transient physical techniques including in situ EPR, in situ SPV and transient laser flash photolysis etc. have also been used to elucidate the interfacial photo-induced redox process and charge-carrier behaviors. We found that hierarchical nanostructured assemblies can be engineered to tailor the properties of external fields modulated and/or light harvesting assemblies. The crystal-, micro- and surface-interface structure could be tailored by utilizing various synthesis strategies, which would incur the nanomaterials with novel PEC/PC properties. Furthermore, combined in - situ spectroscopic characterization could provide more detail structural information and redox process over micro-interface, which would be beneficial for design efficient solar and energy conversion based materials at molecular utilization and/or atomic level. The tailored hierarchical nanomaterials may find novel applications in multidisciplinary fields.

Synthesis, Structural Characterization and Ligand-Enhanced Photo-Induced Color-Changing Behavior of Two Hydrogen-Bonded Ho(III)-Squarate Supramolecular Compounds.

Two coordination polymers (CPs) with chemical formulas, [Ho2(C4O4)2(C2O4)(H2O)8]·4H2O (1) and [Ho(C4O4)1.5(H2O)3] (2), (C4O42− = dianion of squaric acid, C2O42− = oxalate), have been synthesized and their structures were determined by single-crystal X-ray diffractometer (XRD). In compound 1, the coordination environment of Ho(III) ion is eight-coordinate bonded to eight oxygen atoms from two squarate, one oxalate ligands and four water molecules. The squarates and oxalates both act as bridging ligands with μ1,2-bis-monodentate and bis-chelating coordination modes, respectively, connecting the Ho(III) ions to form a one-dimensional (1D) ladder-like framework. Adjacent ladders are interlinked via O–H⋅⋅⋅O hydrogen bonding interaction to form a hydrogen-bonded two-dimensional (2D) layered framework and then arranged orderly in an AAA manner to construct its three-dimensional (3D) supramolecular architecture. In compound 2, the coordination geometry of Ho(III) is square-antiprismatic eight coordinate bonded to eight oxygen atoms from five squarate ligands and three water molecules. The squarates act as bridging ligands with two coordination modes, μ1,2,3-trismonodentate and μ1,2-bis-monodentate, connecting the Ho(III) ions to form a 2D bi-layered framework. Adjacent 2D frameworks are then parallel stacked in an AAA manner to construct its 3D supramolecular architecture. Hydrogen bonding interactions between the squarate ligands and coordinated water molecules in 1 and 2 both play important roles on the construction of their 3D supramolecular assembly. Compounds 1 and 2 both show remarkable ligand-enhanced photo-induced color-changing behavior, with their pink crystals immediately turning to yellow crystals under UV light illumination.

A Visible‐Light‐Induced Dynamic Mechanical Bond as a Linkage for Dynamic Materials

AbstractExploring dynamic bonds and their applications in fabricating dynamic materials has received great attention. A photoinduced [2]rotaxane‐based dynamic mechanical bond (DMB) features visible‐light‐triggered dynamic bonding behavior that is essentially distinguished from conventional dynamic chemical bonds. In this DMB, a photoisomerizable ortho‐fluoroazobenzene unit is introduced as a steric‐controllable stopper, the visible‐light‐induced dynamic wagging movement of which enables the photoregulated threading of the macrocycle. This allows reversible in situ de‐/reforming of the mechanical bond without involving dynamic chemical linkage. The DMB‐cross‐linked polymeric gel shows interesting photoinduced degradation behavior upon visible light irradiation. Benefiting from the distinctive dual dynamic nature of reversible bonding behavior and mechanical interlocked structure, this DMB is expected to serve as a new type of dynamic bond that can be applied in designing dynamic soft materials.

A Visible‐Light‐Induced Dynamic Mechanical Bond as a Linkage for Dynamic Materials

Exploring dynamic bonds and their applications in fabricating dynamic materials has received great attention. A photoinduced [2]rotaxane-based dynamic mechanical bond (DMB) features visible-light-triggered dynamic bonding behavior that is essentially distinguished from conventional dynamic chemical bonds. In this DMB, a photoisomerizable ortho-fluoroazobenzene unit is introduced as a steric-controllable stopper, the visible-light-induced dynamic wagging movement of which enables the photoregulated threading of the macrocycle. This allows reversible in situ de-/reforming of the mechanical bond without involving dynamic chemical linkage. The DMB-cross-linked polymeric gel shows interesting photoinduced degradation behavior upon visible light irradiation. Benefiting from the distinctive dual dynamic nature of reversible bonding behavior and mechanical interlocked structure, this DMB is expected to serve as a new type of dynamic bond that can be applied in designing dynamic soft materials.

Lentinan in-situ coated tungsten oxide nanorods as a nanotherapeutic agent for low power density photothermal cancer therapy

Development of high photothermal performance and biocompatible nanotherapeutic agents is of great importance for photothermal cancer treatment. In this paper, we have developed lentinan decorated tungsten oxide nanorods (W18O49@LTN NRs) via a mild one-step solvothermal route. Owing to the numerous surface hydroxyl groups of polymer chains, the presence of lentinan layer in the surface of W18O49 NRs lead to good biocompatibility. The lentinan layer also affects the crystal structure of W18O49 and improves near-infrared absorption (~1.7 × 109 M−1 cm−1 at 980 nm), which is two orders of higher than previously reported PEGylated W18O49 nanowires. Even under near-infrared (NIR) laser irradiation at a very low power density of 0.4 W/cm2, the temperature of W18O49@LTN NRs aqueous dispersion (125 μg/mL) could increase by 15.1 °C. The photothermal conversion efficiency of W18O49@LTN NRs reaches 33.86%, which is higher than previously reported WO3−x hierarchical nanostructures (28.1%). Importantly, when cancer cells were treated with W18O49@LTN NRs (200 μg/mL) and 980 nm laser (0.4 W/cm2), a significant photo-induced cell killing behavior was observed. This work demonstrates that W18O49@LTN NRs have the potential for precise cancer treatment.

Photoinduced Nonlinear Contraction Behavior in Metal-Organic Frameworks.

The photoinduced dynamic behavior of flexible materials has received considerable attention for potential applications, such as in data storage or as smart optical devices and molecular mechanical actuators. Until now, precisely controlling expansion and contraction with light has remained a challenge. Unraveling the detailed mechanisms of photoinduced structural transformations remains a critical step necessary to understand the molecular architecture necessary for the design of sensitive photomechanical actuators. Herein, a two-dimensional flexible metal-organic framework [Zn2 (bdc)2 (3-CH3 -spy)2 ]⋅H2 O (Zn2 -1; H2 bdc=1,4-benzenedicaboxylic acid; 3-CH3 -spy=3-methylstyrylpyridine) with a positive volumetric thermal expansion coefficient of +78.78×10-6 K-1 is reported. Upon light irradiation at different wavelengths, the MOF underwent a [2+2] cycloaddition, which afforded a family of isomeric, three-dimensional MOFs (Zn2 -2 n, n=a-d) in a single-crystal-to-single-crystal (SCSC) manner. An unprecedented phenomenon, that is, photoinduced nonlinear contraction (PINC), was observed during this conversion. The PINC is caused by conformational changes in the 3-CH3 -spy and bdc2- ligands, the bending of metal-ligand bonds, and the local distortion of the paddle-wheel SBUs. The formation of a "wrinkle morphology" on the crystal surface after the photoreaction was observed by AFM. This PINC behavior can broaden the studies on materials expansion and offer a photodriven approach for the future design of supersensitive photomechanical actuators.

Formation, Photophysics, and Photochemistry of Anionic Lanthanide(III) Mono- and Bisporphyrins.

Since water-soluble porphyrin complexes of lanthanides(III) have proved to be promising for medical applications (e.g., luminescence imaging, photodynamic therapy, and theranostics), the investigation of the formation, photophysical, and photochemical properties of such coordination compounds provides useful pieces of information for their potential usage. Steady-state and time-resolved fluorometry, UV–Vis absorption spectroscopy, and continuous-wave photolysis were utilized for this purpose. 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin formed mono- and bisporphyrin complexes with samarium(III), europium(III), and gadolinium(III) as representatives in the middle of the lanthanide series. The special photoinduced behavior of these compounds was mostly determined by the position of the metal center, which was located out of the ligand plane, thus distorting it. Besides, the photochemical and, especially, photophysical features of the corresponding mono- and bisporphyrin complexes were similar because, in the latter species, two monoporphyrins were connected by a weak metal bridge between the peripheral sulfonato substituents (tail-to-tail dimerization). The formation of these coordination compounds and the transformation reactions between the mono- and bisporphyrins were rather slow in the dark at room temperature. These processes were accelerated by visible irradiation. However, dissociation and, especially, redox degradation were the main photoreactions in these systems, although with low quantum yields. Additionally, depending on the excitation wavelength, new types of photoproducts were also detected.

Photomemristors using carbon nanowall/diamond heterojunctions

Abstract