Changes In Molecular Structure Research Articles

A review of mechanochromic polymers and composites: From material design strategy to advanced electronics application

The design and fabrication of functional polymers with fascinating mechanochromic properties are of profound significance to their prospective applications, such as wearable electronic skin, smart screen, artificial muscle, encryption, and anti-counterfeiting devices. Drawn inspiration from color-changing properties of biological skins, numerous approaches, from molecular synthesis to special biomimicry engineering, have been employed to construct flexible stimuli-responsive materials with superior mechano-stimulated optical change performance. In this review, we highlight and discuss recent important progress in material structure design strategy for mechanochromic polymers and composites. These optical variations primarily originate from the force-induced molecular structure change, disruption of intermolecular interaction, evolution of physical photonic and morphological structure. Moreover, according to their respective structure-property relationships, their multifunctional applications in advanced electronics field are also demonstrated with representative examples. Furthermore, a summary and perspective regarding the existing challenges in this field will be discussed, aiming to provide valuable insight into their future developments. We believe this feature review will bring helpful guidance to readers for choosing effective chromogenic material design method to satisfy different application requirements.

Study on the Microscopic Mechanism of Spontaneous Combustion and Oxidation Kinetics of Water-Leached Coal

In this article, a series of experiments have been carried out to study the spontaneous combustion and oxidation mechanism of coal after water immersion and investigate its tendency to spontaneous combustion, analyze the difficulty of spontaneous combustion of coal samples under different water immersion conditions, and establish a kinetic model of water immersion coal oxidation (taking the Bulianta 12# coal as a case study). They rely on physical oxidation adsorption, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry, and oil bath heating. SEM has been used to analyze the characteristics of coal pore structure under different water immersion conditions (water-saturated coal samples under different water loss conditions until the coal samples are completely dried); FTIR served to investigate the characteristics of the molecular chemical structure of the coal surface before and after the coal is immersed in water. Through programmed temperature oxidation experiments combined with FTIR analyses and gas chromatographic (GC) analysis of gaseous products, it has been possible to study the changes of molecular structure and gas products on the surface of coal samples at different temperatures and water immersion conditions. The oxidation reaction rate of the 12# coal samples of Shendong Mine’s Bulianta Mine under different water content conditions during the spontaneous combustion process has been quantitatively studied. The difficulty of spontaneous combustion of coal samples has been correspondingly addressed. A kinetic model from the perspective of oxygen consumption has been proposed. Thermogravimetry-differential scanning calorimetry (TG-DSC) has been used to analyze and study the exothermal oxidation process before and after coal immersion. From the perspective of the exothermic intensity of the coal-oxygen reaction, an oxidation kinetic model for immersed coal samples has been developed to qualitatively determine its spontaneous combustion tendency. Results have shown that the increase in the specific surface area increases the risk of spontaneous combustion, and coal samples after soaking and drying have a stronger tendency to spontaneous combustion than raw coal. The moisture content of the coal sample leading to the easiest ignition conditions is 16.05%. Regardless of the moisture content, the critical temperature is maintained at 65–75°C, and the temperature of the left coal in the goaf should be prevented from exceeding this critical value.

Analysis of the aging mechanism and life evaluation of elastomers in simulated proton exchange membrane fuel cell environments

Abstract This paper studies the aging mechanism of elastomeric gaskets made from silicone rubbers in simulated proton exchange membrane fuel cells (PEMFCs) in humid, acidic, and high-temperature environments. The changes in the surface morphology are observed using optical microscopy. Attenuated total reflection Fourier transform infrared spectroscopy (AFT-FTIR) and X-ray photoelectron spectroscopy (XPS) are used to investigate the changes in the chemical molecular structure. The stress relaxation test is conducted to characterize the decay process of the mechanical properties. The results indicate that cracks appear on the surface and that the aging mechanism is mainly due to decomposition in the backbone and hydrolysis of the crosslinking. The stress relaxation modulus decreases as the acid concentration increases, which suggests a decrease in elasticity and an increase in brittleness. A master curve that relates time and concentration is constructed. Based on this inference, the experimental time can be shortened by about four times.

Microwave treatment alters the fine molecular structure of waxy hull-less barley starch

Waxy hull-less barley kernels and their isolated starches were exposed to different microwave conditions (power 640, 720, and 800 W, time 60, 120 and 180 s) and changes in morphology, particle size, digestibility, rheological properties, and molecular structure were measured and analyzed. Microwave treatment caused roughness and deformation of granular surfaces, and an increase in granule size. After treatment, the in vitro digestibility of starch was increased, i.e., the RDS increased, but the RS decreased. Microwave treatment decreased the K values of the in-kernel MWI WHBS. Dynamic rheological results showed that the in-kernel MWI WHBS pastes had lower TG′max, and higher G′max, G′90°C, G′25°C, G′0.1Hz and G′20Hz after treatment. The chain-length distribution did not significantly change after microwave treatment. However, the results for molecular size distributions showed that the peaks of amylopectin (Rh = ~100 nm) shifted left and right, indicating that the molecular volume might become smaller or larger under different processing conditions. The primary effects of microwave treatment may be loosening the molecular structure and cutting main chains of amylopectin.

Textile integrable mechanochromic strain sensor based on the interplay of supramolecular interactions

Mechanochromic materials, when exposed to mechanical deformation, undergo a modification of optical properties. This behaviour can stem from either conformational rearrangements, disruptions of intermolecular interactions, or molecular structure changes affecting absorption, emission, or reflection abilities. Here reversible colour change of Disperse Red 1/polyvinylpyrrolidone films resulting from humidity annealing and subsequent stretching is reported. Due to the humidity-induced blue shift of the absorbance peak related to exciton coupling of the chromophores, the tone of films abruptly changes from red to orange. Upon stretching, the gradual disaggregation of the chromophores takes place and therefore the colour switches back to red in a stepless manner. Using either red–green–blue analysis of time lapse photography or UV–Visible measurements, this transformation, which is also well visible by the naked eye, can be followed with high accuracy. This work offers the opportunity to apply the strain sensor in humid environments to prevent the mechanical failures by showing a colour change in areas subjected to undesired stress. Moreover, dip-coating yarns with mechanochromic coating allows fabrication of functional yarns that change their colour based on their stretching state – thus enabling preparation of colour-changing stretchable textiles was demonstrated.

Infrared study and computational simulations of coronary arteries atherosclerotic lesions for early diagnosis of disease progression

Abstract Introduction Coronary artery atherosclerotic disease is the most common cardiovascular disease and bypass grafting surgery (CABG) is an effective treatment. However, the pathogenic mechanism of coronary arteries atherosclerosis and disease progression is not yet clear. Purpose The use of FT-IR spectroscopy, hyperspectral microscope and mathematical simulation models are some of the tools to predict the morphological and elasticity disorders in the vessel wall due to molecular structure changes. Methods Biopsies of atherosclerotic native coronary arteries from 54 patients (44–85 years), who underwent coronary endarterectomy during bypass grafting surgery (CABG), were examined ex vivo. The FT-IR-spectra were recorded with a Nicolet-6700 spectrometer. Morphological changes of atheromatic plaques were performed with SEM-EDX, Fei-Co. CytoVita-Olympus hyperspectral microscope was used to obtain the cells. Results FT-IR spectroscopy (Figure 1A) showed that the disease affects the protein folding, leading to amyloid formation (beta-sheets), lipid peroxidation and AGEs (Advanced Glycation end products) production. The detection of amorphous CaCO3 (1415 and 872 cm–1) deposits in high lipophilic regions was of high importance. Increased mineral concentration leads to increased formation of crystalline deposits, consisting of CaCO3, CaHPO4, Ca3(PO4)2 and inorganic hydroxyapatite, resulting in arterial stenosis. Hyperspectral images confirmed the formation of micelles (1) due to amyloidosis and calcified cells (2), in agreement with FT-IR, ImageJ analysis data. Mathematical simulation model based on finite element method (Figure 1E) showed that arterial wall damage and elasticity changes were not homogenous. This model provides the time of crystallization of the calcium salts, which play crucial role to stenosis. Conclusions FT-IR spectra showed that the formation of amorphous CaCO3 in the presence of Mg2+, in reach of oxidized lipids regions, inhibit the development of coronary artery stenosis. Excessive of Ca2+ efflux promotes the crystallinity of CaCO3 and Ca3(PO4)2 deposits, leading to the development of atherosclerotic plaques and coronary artery stenosis. Mathematical models approach in a much better way the progression of arterial atherosclerosis. Funding Acknowledgement Type of funding sources: None. Figure 1

PSXIII-1 Effect of varieties and processing methods on physicochemical, nutritional, molecular structural characteristics of feed chickpeas

Abstract The objectives of this study were to evaluate the effect of varieties and heat processing methods on molecular structural, physicochemical, and nutritional characterization of feed chickpeas; evaluate the effect of heat processing methods, dry heat, wet heat and microwave irradiation processing method on feed chickpeas as an alternative source for protein and energy feed for ruminant livestock. To reveal the molecular structure spectral profile of chickpeas varieties and the molecular structure changes when applied heat processing methods, vibrational molecular spectroscopy was applied. Feed chickpea samples were determined for chemical profile, energy values, carbohydrate fractions. Subsequently, chickpea samples were incubated in the rumen of dairy cows for degradation kinetics analysis of nutrients. The intestinal digestion of feed chickpea samples was determined using three-step in vitro method with pre-incubation at 16h. Later, protein and carbohydrate related molecular spectral features before and after incubation were performed using vibrational ATR-FTIR molecular spectroscopy. The interactive relationship between processing induced molecular spectral profile changes and nutrient metabolism and availability were studied. The available results showed that varieties and heat processing methods significantly impacted molecular structural, physicochemical, and nutritional characterization of feed chickpeas.

PSXVI-26 Using synchrotron/globar techniques to reveal synergistic and interactive association between molecular structures and nutrient supply in enzymatic and thermal treated oat tissue and whole grain

Abstract As an advanced technique, synchrotron radiation-based microspectroscopy SR-FTIRM has been a rapid, direct, non-destructive and non-invasive bioanalytical method. Globar molecular spectroscopic technique -attenuated total reflectance-ATR-FTIR spectroscopy will be used. For this research, feed type CDC Nasser, forage type CDC haymaker, and milling types CDC Arborg and Summit with three consecutive years are studied. There are three treatments for oat samples: Treatment 1, steam pressure processing alone; Treatment 2, adding innovative fibrolytic enzyme; Treatment 3, steam pressure processing plus fibrolytic enzyme. Each treatment combination has three replications. The objectives of this research are to detect the molecular structure spectral features of processed oat endosperm tissues at a molecular and cellular level in relation to chemical profiles, protein and carbohydrate fractions, energy profiles, degradation kinetics, intestinal digestibility, microbial protein production and true nutrient supply of whole oat grains. This research reveals the interactive association between induced molecular structure changes and nutrient properties and true nutrient supply. This research is also to increase economic returns to oat producers and related dairy industries through efficient utilization of feed-type or milling type of oat grains.

Spectroscopic Explore (Ft-Ir, Ft-Raman) with Homo-Lumo, Admet and Molecular Docking Studies of 5, 7-Dihydroxy-2-(4-Hydroxyphenyl) Chroman-4-One Against Lung Cancer: A Potential Uptake B-Raf Inhibitor

Naringenin has been shown to have an anti-cancer effect by suppressing cell growth, although the role of Naringenin in lung cancer and the molecular processes by which it works are yet unknown. Naringenin is chemically called 5, 7-Dihydroxy-2-(4-hydroxyphenyl) chroman-4-one. To find the optimized geometrical structure, Vibrational frequencies and Intensity of Naringenin were theoretical characterizations using density functional theory with basis set 6-311G (d,p) was compared with Experimental FTIR and FT-Raman Spectroscopic Characterization. The Energy value of Naringenin molecules was analyzed with HOMO-LUMO energies. ADMET and Drug likeness of the title compound was predicted. Molecular structural changes, distribution and reactive site investigated with MEP (Molecular Electrostatic Potential). The density of state (DOS) used to know molecular orbital contribution is necessary for molecular reactivity. A molecular docking analysis and the conformational changes and electrostatic properties are useful to understand of Naringenin molecule in the active site of BRAF Receptor is essential for future chemotherapy agents in lung cancer

Roles of key residues and lipid dynamics reveal pHLIP-membrane interactions at intermediate pH

The pH-low insertion peptide (pHLIP) and its analogs sense the microenvironmental pH variations in tumorous cells and serve as useful anticancer drug deliveries. The pHLIP binds peripherally to membranes and adopts random coil conformation at the physiological pH. The peptide switches from random coil to α-helical conformation and inserts unidirectionally into membrane bilayers when pH drops below a critical transition value that has been routinely determined by the Trp fluorescence spectroscopy. Recent high-resolution studies using solid-state NMR spectroscopy revealed the presence of thermodynamically stable intermediate states of membrane-associated pHLIP around the fluorescence-based transition pH-value. However, the molecular structural features and their mechanistic roles of these intermediate states in the pH-driven membrane insertion process of pHLIP remain largely unknown. This work utilizes solid-state NMR spectroscopy to explore 1) the mechanistic roles of key proline and arginine residues within the pHLIP sequence at intermediate pH-values, and 2) the changes in lipid dynamics at intermediate pH-values in multiple types of model bilayers with anionic phospholipid and/or cholesterol. Our results demonstrate several molecular structural and dynamics changes at around the transition pH-values, including the isomerization of proline-threonine backbone configuration, breaking of arginine-aspartic acid salt bridge and the formation of arginine-lipid interactions, and a universal decreasing of dynamics in lipid headgroups and alkyl chains. Overall, the outcomes provide important insights on the molecular interactions between pHLIP and membrane bilayers at intermediate pH-values and, therefore, prompt the understanding of pH-driven membrane insertion process of this anticancer drug-delivering peptide.

Effect of Molecular Structure on Electrochemical Phase Behavior of Phospholipid Bilayers on Au(111).

Lipid bilayers form the basis of biological cell membranes, selective and responsive barriers vital to the function of the cell. The structure and function of the bilayer are controlled by interactions between the constituent molecules and so vary with the composition of the membrane. These interactions also influence how a membrane behaves in the presence of electric fields they frequently experience in nature. In this study, we characterize the electrochemical phase behavior of dipalmitoylphosphatidylcholine (DPPC), a glycerophospholipid prevalent in nature and often used in model systems and healthcare applications. DPPC bilayers were formed on Au(111) electrodes using Langmuir-Blodgett and Langmuir-Schaefer deposition and studied with electrochemical methods, atomic force microscopy (AFM) and in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). The coverage of the substrate determined with AFM is in accord with that estimated from differential capacitance measurements, and the bilayer thickness is slightly higher than for bilayers of the similar but shorter-chained lipid, dimyristoylphosphatidylcholine (DMPC). DPPC bilayers exhibit similar electrochemical response to DMPC bilayers, but the organization of molecules differs, particularly at negative charge densities. Infrared spectra show that DPPC chains tilt as the charge density on the metal is increased in the negative direction, but, unlike in DMPC, the chains then return to their original tilt angle at the most negative potentials. The onset of the increase in the chain tilt angle coincides with a decrease in solvation around the ester carbonyl groups, and the conformation around the acyl chain linkage differs from that in DMPC. We interpret the differences in behavior between bilayers formed from these structurally similar lipids in terms of stronger dispersion forces between DPPC chains and conclude that relatively subtle changes in molecular structure may have a significant impact on a membrane's response to its environment.

Kinetic analysis of the effect of O2 on SF6 over-thermal decomposition

Partial over-thermal fault (POF) may occur during the operation of SF6 gas insulated equipment, which will cause SF6 to decompose and threaten the safety of equipment and stable operation of power grid. The decomposition of SF6 is closely related to the residual O2 inside the equipment. The decomposition mechanism of SF6 under the action of O2 needs to be studied in depth but there is still a lack of a force field to describe it. This paper first establishes a reactive force field (ReaxFF) that can describe the microscopic reaction process of SF6 and O2 coexisting systems. Using the force field, a series of molecular dynamics (MD) simulations are performed to explore the effect of O2 on the over-thermal decomposition of SF6. First, the main chemical reactions affecting the formation of the characteristic products were obtained. Second, the decomposition process of SF6 and O2 with different proportions is studied, and the kinetic process of reactions are observed, which simulates the changes in quantity of the major products including SOF4, SOF3, SOF2, SO2F2, SOF and SO2. In addition, transition state theory is used to study the changes in energy and molecular structure during the reaction. Synthesizing the simulation results, the mechanism of O2 on the over-thermal decomposition of SF6 is analysed. This work advances our understanding of the mechanism of over-thermal failure of gas insulated equipment.

Topological Analysis of Magnetically Induced Current Densities in Strong Magnetic Fields Using Stagnation Graphs

Stagnation graphs provide a useful tool to analyze the main topological features of the often complicated vector field associated with magnetically induced currents. Previously, these graphs have been constructed using response quantities appropriate for modest applied magnetic fields. We present an implementation capable of producing these graphs in arbitrarily strong magnetic fields, using current-density-functional theory. This enables us to study how the topology of the current vector field changes with the strength and orientation of the applied magnetic field. Applications to CH4, C2H2 and C2H4 are presented. In each case, we consider molecular geometries optimized in the presence of the magnetic field. The stagnation graphs reveal subtle changes to this vector field where the symmetry of the molecule remains constant. However, when the electronic state and symmetry of the corresponding equilibrium geometry changes with increasing field strength, the changes to the stagnation graph are extensive. We expect that the approach presented here will be helpful in interpreting changes in molecular structure and bonding in the strong-field regime.

Dynamic Spin-Spin Interaction Observed as Interconversion of Chemical Bonds in Stepwise Two-Photon Induced Photochromic Reaction.

Biradicaloids in π-conjugated organic molecules have been extensively studied in recent years because of the fundamental insights into the chemical bonds and unique optical, electrical, and magnetic properties. Several studies have reported that the spin-spin interactions of biradicaloids with flexible molecular frameworks dynamically evolve correlating with molecular structural changes. Although these dynamic behaviors will provide important insights into the relationship between molecular structures and spin properties, studies on such behaviors have been limited to two-spin systems. Here, we investigated the stepwise photochromic properties of biphotochromic molecules involving multiple spin interactions by double-pulse laser flash photolysis. The one-photon photochromic reaction generates the o-biradical form as the open-closed form, which thermally isomerizes to the o-quinoidal form and reaches the thermal equilibrium state between them. The additional absorption of a photon by the open-closed form leads to the photochromic reaction of the other photochromic unit, resulting in the generation of unpaired spins at the p-position of the central aromatic bridge of the biradical or quinoidal form. Under the situation, while the interaction between the unpaired spins and the o-biradical preferentially produces the p-quinoidal form in which the antiferromagnetic interaction at the p-position is dominant, that between the spins and the o-quinoidal form kinetically produces the bis(o-quinoidal) form followed by the thermal isomerization to the thermodynamically stable p-quinoidal form. These dynamic spin-spin interactions along with the rearrangement of chemical bonds will give a deeper understanding of the singlet biradicaloids and that to bridge organic multiradicals in molecular systems to cooperative spin behaviors in bulk materials.

Switching the Local Symmetry from D5h to D4h for Single-Molecule Magnets by Non-Coordinating Solvents

A solvent effect towards the performance of two single-molecule magnets (SMMs) was observed. The tetrahydrofuran and toluene solvents can switch the equatorial coordinated 4-Phenylpyridine (4-PhPy) molecules from five to four, respectively, in [Dy(OtBu)2(4-PhPy)5]BPh41 and Na{[Dy(OtBu)2(4-PhPy)4][BPh4]2}∙2thf∙hex 2. This alternation significantly changes the local coordination symmetry of the Dy(III) center from D5h to D4h for 1 and 2, seperately. Magnetic studies show that the magnetic anisotropy energy barrier of 2 is higher than that of 1, while the relation of blocking temperature is just on the contrary due to the symmetry effect. The calculations of the electrostatic potential successfully explained the driving force of solvents for the molecular structure change, confirming the feasibility of adjusting the performance of SMMs via diverse solvents.

Correlating Antiagglomerant Performance with Gas Hydrate Cohesion.

Although inhibiting hydrate formation in hydrocarbon-water systems is paramount in preventing pipe blockage in hydrocarbon transport systems, the molecular mechanisms responsible for antiagglomerant (AA) performance are not completely understood. To better understand why macroscopic performance is affected by apparently small changes in the AA molecular structure, we perform molecular dynamics simulations. We quantify the cohesion energy between two gas hydrate nanoparticles dispersed in liquid hydrocarbons in the presence of different AAs, and we achieve excellent agreement against experimental data obtained at high pressure using the micromechanical force apparatus. This suggests that the proposed simulation approach could provide a screening method for predicting, in silico, the performance of new molecules designed to manage hydrates in flow assurance. Our results suggest that entropy and free energy of solvation of AAs, combined in some cases with the molecular orientation at hydrate-oil interfaces, are descriptors that could be used to predict performance, should the results presented here be reproduced for other systems as well. These insights could help speed up the design of new AAs and guide future experiments.

Radical Photopolymerization Using 1,4-Dihydropyrrolo[3,2-b]pyrrole Derivatives Prepared via One-Pot Synthesis.

Radical photopolymerization has attracted significant attention for manufacturing products with complicated structures. Herein, the synthesized 1,4-bis(4-bromophenyl)-2,5-bis(4-nitrophenyl)-1,4-dihydropyrrole[3,2-b]pyrrole (PyBN) is found to show varying photoactivity upon irradiation at different wavelengths. PyBN affords two main absorption bands, and its maximum absorption peak is at 462 nm, attributing to its strong intramolecular charge transfer property based on the donor–acceptor structure. It efficiently photoinitiates the radical photopolymerization of different (meth)acrylate materials under 365 and 395 nm LED irradiation. The highest double bond conversion of 99.86% is achieved for these materials. Under 470 nm LED, PyBN does not show molecular structure change from photolysis results as a result of intramolecular charge transfer. Therefore, PyBN shows wavelength-selective photoactivity with potential application in dual-wavelength volumetric additive manufacturing. A unique solid product is successfully fabricated using a 365 nm LED with co-irradiation of a 470 nm LED. Additionally, PyBN incorporating camphorquinone (CQ) as a two-component visible light photoinitiator system is investigated under 470 nm LED irradiation. As PyBN has a charge transfer activity at 470 nm, the combination with CQ exhibits a good synergistic interaction. Besides nitro-based PyBN, a methyl-based PyBC was prepared as a reference compound.

Following in Emil Fischer's Footsteps: A Site-Selective Probe of Glucose Acid-Base Chemistry.

Liquid-jet photoelectron spectroscopy was applied to determine the first acid dissociation constant (pKa) of aqueous-phase glucose while simultaneously identifying the spectroscopic signature of the respective deprotonation site. Valence spectra from solutions at pH values below and above the first pKa reveal a change in glucose’s lowest ionization energy upon the deprotonation of neutral glucose and the subsequent emergence of its anionic counterpart. Site-specific insights into the solution-pH-dependent molecular structure changes are also shown to be accessible via C 1s photoelectron spectroscopy. The spectra reveal a considerably lower C 1s binding energy of the carbon site associated with the deprotonated hydroxyl group. The occurrence of photoelectron spectral fingerprints of cyclic and linear glucose prior to and upon deprotonation are also discussed. The experimental data are interpreted with the aid of electronic structure calculations. Our findings highlight the potential of liquid-jet photoelectron spectroscopy to act as a site-selective probe of the molecular structures that underpin the acid–base chemistry of polyprotic systems with relevance to environmental chemistry and biochemistry.

Development of Polythiophene–Tripeptide Covalent Conjugates Showing Excellent Structure-Dependent Photophysical and Photocurrent Properties

Presently, conducting polymer–peptide conjugates have drawn great interest for their interesting optoelectronic and photophysical properties. To understand the structural dependence of the conjugates on their properties, we have covalently coupled poly(3-thiophene acetic acid) (P3TAA) with a C-protected tripeptide, H2N-F-F-V-OMe (TPEP), to produce their conjugate PTCP-I. A carboxylic acid-deprotected tripeptide polythiophene conjugate (PTCP-II) is also produced by alkaline hydrolysis of PTCP-I to delineate any difference in properties due to the change in molecular structure. The stretching frequencies for −NH– and >C═O groups of PTCP-II are 11 and 26 cm–1 lower than those of PTCP-I, indicating better intermolecular hydrogen bonding interactions in the former. This alters the seaweed morphology of PTCP-I to a sheet morphology for PTCP-II. The blue shift of the π–π* absorption band of polythiophene with gradually increasing the PTCP-I concentration is attributed to the H-type aggregation in DMF solution, but in the solid state, this peak shows a 17 nm red shift from its solution state for better electron delocalization for closer proximity of molecules. The UV–Vis peak of PTCP-II shows a lower blue shift than that of PTCP-I in DMF, attributed to the uncoiled polythiophene chains of the former. In DMF solution, interestingly, both PTCP-I and PTCP-II conjugates exhibit aggregation-induced emission (AIE), showing maxima at 0.08 mg/mL and then aggregation-induced quenching (AIQ) with further increasing its concentration. PTCP-I and PTCP-II exhibit dc conductivities of 0.04 and 0.55 μS cm–1, respectively, at 30 °C, and the higher value for PTCP-II is due to its lower band gap (1.91 eV) compared to that of PTCP-I (2.14 eV). The current (I)–voltage (V) plot of both conjugates exhibits semiconducting properties, which are higher for PTCP-II for its lower band gap. The photocurrent behavior of the conjugates indicates that the on–off response in the PTCP-II system is significantly higher than that in PTCP-I due to the unfolded polymer chain of the former, as the photogenerated electrons and holes can move more freely there. Impedance spectra of both the conjugates show single semicircles for the Nyquist plots, and the charge transfer resistance of PTCP-II is 4.4 times lower than that of PTCP-I but the capacitance value is 27 times higher, arising from the more extended chain configuration of the former, signifying structural importance on the optoelectronic and photocurrent properties of the polymer–peptide conjugates.

Stimulus-Responsive Room Temperature Phosphorescence Materials: Internal Mechanism, Design Strategy, and Potential Application

ConspectusRoom temperature phosphorescence (RTP) materials, which could respond to external stimuli, such as force, heat, light, electric filed, etc., have drawn increasing attention for their broad application prospects, especially in the fields of anticounterfeiting, sensors, data storage, and so on. In comparison with the traditional fluorescence ones, RTP materials show much longer emission lifetimes, which can be even caught by the naked eye. Thus, the change in emission lifetime under an external stimulus for RTP materials can be also a potential monitoring parameter, in addition to emission color and intensity. In other words, the number of visual monitoring parameters could increase from two to three in RTP materials, which would greatly facilitate their practical applications. Until now, RTP materials have been typically limited to metal-containing inorganic materials, particularly rare-earth phosphors. Their emissions are governed by the slow liberation of trapped charge carriers from isolated traps of impurities, defects, or ions through thermal stimulation with low luminescence efficiency. However, these materials suffer from some intrinsic disadvantages, including high cost, potential toxicity, and instability in aqueous environments. In order to solve these problems, the purely organic RTP materials should be a good choice. However, these kinds of materials are really scarce now, especially for the ones with stimulus response characteristic.To develop purely organic RTP materials with a stimulus response effect, we and other scientists have tried a lot. Luckily, some progresses have been made. In this Account, we present our recent progress on the stimulus-responsive room temperature phosphorescence of organic materials, mainly focusing on the internal mechanism and potential applications. First, the fundamental knowledge is described to illustrate the importance and main principles of the stimulus-responsive RTP effect. Then, some typical stimulus-responsive RTP materials based on different internal mechanisms are discussed. Mainly, two kinds of stimulus-responsive RTP materials were introduced, namely, single-component and multicomponent ones. Correspondingly, their dynamic change of the RTP property under external stimulus occurred based on the distinct internal mechanisms. For single-component materials, the changes in molecular structure, packing, or conformation, have played a significant role in their corresponding stimulus-responsive RTP effect. As for multicomponent materials, the changed oxygen concentration in matrix and intermolecular distance between different components were found more during the stimulus-responsive RTP process. Accordingly, different potential applications were explored based on the different stimulus-responsive RTP processes. With the classification of stimulus-responsive RTP materials based on different internal mechanisms, the corresponding design strategy could be well proposed, thus guiding the further development of this research field.