Photoinduced Pedalo‐Type Motion in an Azodicarboxamide‐Based Molecular Switch

Well‐defined structural changes of molecular units that can be triggered by light are crucial for the development of photoactive functional materials. Herein, we report on a novel switch that has azodicarboxamide as its photo‐triggerable element. Time‐resolved UV‐pump/IR probe spectroscopy in combination with quantum‐chemical calculations shows that the azodicarboxamide functionality, in contrast to other azo‐based chromophores, does not undergo trans–cis photoisomerization. Instead, a photoinduced pedalo‐type motion occurs, which because of its volume‐conserving properties enables the design of functional molecular systems with controllable motion in a confined space.     

Time‐Resolved Interception of Multiple‐Charge Accumulation in a Sensitizer–Acceptor Dyad

Biomimetic models that contain elements of photosynthesis are fundamental in the development of synthetic systems that can use sunlight to produce fuel. The critical task consists of running several rounds of light‐induced charge separation, which is required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur. Long‐lived first charge‐separated state and distinct electronic signatures for the sequential charge accumulated species are essential features to be able to track these events on a spectroscopic ground. Herein, we use a double‐excitation nanosecond pump–pump–probe experiment to interrogate two successive rounds of photo‐induced electron transfer on a molecular dyad containing a naphthalene diimide (NDI) linked to a [Ru(bpy)₃]²⁺ (bpy=bipyridine) chromophore by using a reversible electron donor. We report an unprecedented long‐lived two‐electron charge accumulation (t =200 μs).     

Pump‐Pump‐Probe Spectroscopy of a Molecular Triad Monitoring Detrimental Processes for Photoinduced Charge Accumulation

Controlling light‐induced accumulation of electrons or holes is desirable in view of multi‐electron redox chemistry, for example for the formation of solar fuels or for photoredox catalysis in general. Excitation with multiple photons is usually required for electron or hole accumulation, and consequently pump‐pump‐probe spectroscopy becomes a valuable spectroscopic tool. In this work, we excited a triarylamine‐Ru(bpy)₃²⁺‐anthraquinone triad (bpy = 2,2′‐bipyridine) with two temporally delayed laser pulses of different color and monitored the resulting photoproducts. Absorption of the first photon by the Ru(bpy)₃²⁺ photosensitizer generated a triarylamine radical cation and an anthraquinone radical anion by intramolecular electron transfer. Subsequent selective excitation of either one of these two radical ion species then induced rapid reverse electron transfer to yield the triad in its initial (ground) state. This shows in direct manner that after absorption of a first photon and formation of the primary photoproducts, the absorption of a second photon can lead to unproductive electron transfer events that counteract further charge accumulation. In principle, this problem is avoidable by careful excitation wavelength selection in combination with good molecular design.     

1,2‐Dithienyldicyanoethene‐Based,Visible‐Light‐Driven,Chiral Fluorescent Molecular Switch: Rewritable Multimodal Photonic Devices

Reported here is the first example of a 1,2‐dithienyldicyanoethene‐based visible‐light‐driven chiral fluorescent molecular switch that exhibits reversible trans to cis photoisomerization. The trans form in solution almost completely transforms into the cis form, accompanied by a 10‐fold decrease in its fluorescence intensity within 60 seconds when exposed to green light (520 nm). The reverse isomerization proceeds upon irradiation with blue light (405 nm). When doped into commercially available achiral liquid crystal hosts, this molecular switch efficiently induces luminescent helical superstructures, that is, a cholesteric phase. The intensity of the circularly polarized fluorescence as well as the selective reflection wavelength of the induced cholesteric phases can be reversibly tuned using visible light of two different wavelengths. Optically rewritable photonic devices using cholesteric films containing this molecular switch are described.     

1,2‐Dithienyldicyanoethene‐Based,Visible‐Light‐Driven,Chiral Fluorescent Molecular Switch: Rewritable Multimodal Photonic Devices

Reported here is the first example of a 1,2‐dithienyldicyanoethene‐based visible‐light‐driven chiral fluorescent molecular switch that exhibits reversible trans to cis photoisomerization. The trans form in solution almost completely transforms into the cis form, accompanied by a 10‐fold decrease in its fluorescence intensity within 60 seconds when exposed to green light (520 nm). The reverse isomerization proceeds upon irradiation with blue light (405 nm). When doped into commercially available achiral liquid crystal hosts, this molecular switch efficiently induces luminescent helical superstructures, that is, a cholesteric phase. The intensity of the circularly polarized fluorescence as well as the selective reflection wavelength of the induced cholesteric phases can be reversibly tuned using visible light of two different wavelengths. Optically rewritable photonic devices using cholesteric films containing this molecular switch are described.     

古紫质AR4重组的磷脂脂质体中的定向自组装

This paper reports, for the first time, that Archaerhodopsin-4 (AR4) could be reconstituted into phospholipid liposomes by self-assembly. AR4 is a new membrane protein isolated from halobacteria H.sp. xz515 in a salt lake of Tibet, China. This is a bacteriorhodopsin (bR) like protein, function as a light-driven proton pump. Experimental measurements verified that similar to bR, AR not only remains its biological activity in pmteoliposome, but also keeps a preferred orientation in self-assembly.     

External‐Photocatalyst‐Free Visible‐Light‐Mediated Synthesis of Indolizines

A visible‐light‐mediated synthesis of valuable polycyclic indolizine heterocycles from easily accessed brominated pyridine and enol carbamate derivatives has been developed. This process, which operates at room temperature under irradiation from readily available light sources, does not require the addition of an external photocatalyst. Instead, an investigation into the reaction mechanism indicates that the indolizine products themselves may be in some way involved in mediating and accelerating their own formation. Preliminary studies also show that these simple heterocyclic compounds may be capable of facilitating other visible‐light‐mediated transformations.     

On the Resolution Limit of Femtosecond Stimulated Raman Spectroscopy: Modelling Fifth‐Order Signals with Overlapping Pulses

Femtosecond stimulated Raman scattering (FSRS) spectroscopy is a powerful pump–probe technique that can track electronic and vibrational dynamics with high spectral and temporal resolution. The investigation of extremely short‐lived species, however, implies deciphering complex signals and is ultimately hampered by unwanted nonlinear effects once the time resolution limit is approached and the pulses overlap temporally. Using the loop diagrams formalism we calculate the fifth‐order response of a model system and address the limiting case where the relevant dynamics timescale is comparable to the pump–pulse duration and, consequently, the pump and the probe overlap temporally. We find that in this regime, additional diagrams that do not contribute for temporally well separated pulses need to be taken into account, giving rise to new time‐dependent features, even in the absence of photoinduced dynamics and for negative delays.     

Conjugated‐Polyelectrolyte‐Based Polyprodrug: Targeted and Image‐Guided Photodynamic and Chemotherapy with On‐Demand Drug Release upon Irradiation with a Single Light Source

Nanomaterials that combine diagnostic and therapeutic functions within a single nanoplatform are highly desirable for molecular medicine. Herein we report a novel theranostic platform based on a conjugated‐polyelectrolyte (CPE) polyprodrug that contains functionality for image, chemo‐ and photodynamic therapy (PDT), and on‐demand drug release upon irradiation with a single light source. Specifically, the PEGylated CPE serves as a photosensitizer and a carrier, and is covalently conjugated to doxorubicin through a linker that can be cleaved by reactive oxygen species (ROS). Under appropriate light irradiation, the CPE can generate ROS, not only for PDT, but also for on‐demand drug release and chemotherapy. This nanoplatform will offer on‐demand PDT and chemotherapy with drug release triggered by one light switch, which has great potential in cancer treatment.     

Photoswitchable and Water‐Soluble Fluorescent Nano‐Aggregates Based on a Diarylethene–Dansyl Dyad and Liposome

In this work, a unique approach is developed to generate photoswitchable and water‐soluble fluorescent nano‐aggregates. Initially, a new light‐controlled diarylethene–dansyl dyad DAE 1 is formed by linking two dansyl fluorophores covalently to a symmetrical dithienylethene backbone, whose photophysical properties can be reversibly switched by optical stimuli. Subsequently, the water insolubility of the molecular switch 1 is overcome by incorporating it into the bilayer of liposome DPPC (1,2‐dihexadecanoyl‐sn ‐glycero‐3‐phosphocholine) in water. This strategy creates stable fluorescent nano‐aggregates OF‐1@DPPC (≈25 nm diameter) that are soluble in an aqueous medium. The nano‐aggregates OF‐1@DPPC retain and even improve the photoswitchable fluorescence properties of DAE 1 . More importantly, OF‐1@DPPC exhibits a remarkable photostability and fatigue resistance after 5 cycles of irradiation with UV and visible light, which is crucial for its practical application.     

Polymeric micro‐sequential concentric transcrystalline morphology self‐assembly,with intermittent self‐shear‐oriented amorphous layers

The investigation and understanding of polymer crystallization processes, the resulting crystalline morphologies, and the mechanism of their formation is crucial in creating materials with desired properties for specific applications. The present research introduces and investigates a new polymeric crystalline morphology, observed for the first time in this research. This newly observed morphology, is a sequentially micro‐multi‐layered concentric morphology that self‐assembles throughout the bulk polymer matrix, with intermittent self‐shear‐oriented amorphous layers. The research analyses the structure and mechanism of its formation. Polarized light microscopy studies have shown a drastic and sudden morphology change that occurred during crystalline growth. Crystalline‐growth kinetics studies performed, showed a distinct pulsatile repeating growth pattern of approximately two growth pulses per second. Thermal analysis indicated the presence of two different populations of crystalline strength. Crystalline structure was analyzed by XRD pattern measurements. It was demonstrated here, that the sequential concentric transcrystalline morphology is nucleated on a shear‐oriented amorphous molecular layer in the adjacent melt formed during and as a consequence of crystalline growth, which occurs in a micro‐periodic sequences, with intermittent self‐sheared amorphous layers. The structure was confirmed by both scanning electron microscope and reflectance microscopy. Small angle X‐ray scattering measurements of the same materials reported in literature are consistent with the melt shear‐orientation theory described earlier. The discovery of this new crystalline morphology in this research, potentially opens a new door in the vast field of material properties and applications. Copyright © 2017 John Wiley & Sons, Ltd.     

On‐Tip Photo‐Modulated Molecular Printing

The concept of using cantilever‐free scanning probe arrays as structures that can modulate nanoscale ink flow and composition with light is introduced and evaluated. By utilizing polymer pen arrays with an opaque gold layer surrounding the base of the transparent polymer pyramids, we show that inks with photopolymerizable or isomerizable constituents can be used in conjunction with light channelled through the pyramids to control ink viscosity or composition in a dynamic manner. This on‐tip photo‐modulated molecular printing provides novel chemically and mechanically controlled approaches to regulating ink transport and composition in real time and could be useful not only for rapidly adjusting feature size but also for studying processes including photoreactions and mass transport at the nanoscale, self‐assembly, and cell–material interactions.     

DFT/TDDFT Studies on the Electronic Structures and Spectral Properties of Carbazole‐based Blue Light‐emitting Dendrimers

The purpose of this paper is to provide an in‐depth investigation of the electronic and optical properties of two series of carbazole‐based blue light‐emitting dendrimers, including 1 – 6 six oligomers. These materials show great potential for application in organic light‐emitting diodes as efficient blue‐light and red‐light emitting materials due to the tuning of the optical and electronic properties by the use of different electron donors (D) and electron acceptors (A). The geometric and electronic structures of these compounds in the ground state are calculated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states were optimized by ab initio single excitation configuration interaction (CIS). All DFT calculations are performed using the B3LYP functional on 6‐31G* basis set. The outcomes show that the highest occupied molecular orbitals (HOMOs), lowest occupied molecular orbitals (LUMOs), energies gaps, ionization potentials, electron affinities and reorganization energies of each molecular are affected by different D and A moieties and different substitute positions.     

Self‐Assembly of Aggregation‐Induced‐Emission Molecules

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.     

Non‐born–oppenheimer nuclear and electronic densities for a hooke‐coulomb model for a four‐particle system

Based on the exact solutions for a non‐Born–Oppenheimer (nBO) Hooke‐Coulomb model for a four‐particle system (J. Chem. Phys. 2005, 123, 024102), we present here nBO nuclear and electron one‐particle densities for this system. We examine the effect on the topology of the one‐particle densities that arises from the selection of different reference points for the densities. In addition, we analyze the behavior of these densities as a function of the mass ratio between light and heavy particles. We conclude from these results that molecular structure is not univocally related to the topology of the one‐particle densities in a nBO regime. © 2012 Wiley Periodicals, Inc.     

Pump‐Probe Fragmentation Action Spectroscopy: A Powerful Tool to Unravel Light‐Induced Processes in Molecular Photocatalysts

We present a proof of concept that ultrafast dynamics combined with photochemical stability information of molecular photocatalysts can be acquired by electrospray ionization mass spectrometry combined with time‐resolved femtosecond laser spectroscopy in an ion trap. This pump‐probe “fragmentation action spectroscopy” gives straightforward access to information that usually requires high purity compounds and great experimental efforts. Results of gas‐phase studies on the electronic dynamics of two supramolecular photocatalysts compare well to previous findings in solution and give further evidence for a directed electron transfer, a key process for photocatalytic hydrogen generation.     

Visible‐Light‐Driven Halogen Bond Donor Based Molecular Switches: From Reversible Unwinding to Handedness Inversion in Self‐Organized Soft Helical Superstructures

Visible‐light‐driven molecular switches endowing reversible modulation of the functionalities of self‐organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room‐temperature achiral liquid crystal host 5CB, which also acts as a halogen‐bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible‐light‐driven reversible unwinding, that is, a cholesteric–nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible‐light‐driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented.     

Luminescent,Oxygen‐Supplying,Hemoglobin‐Linked Conjugated Polymer Nanoparticles for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising method for cancer treatment. Two parameters that influence the efficacy of PDT are the light source and oxygen supply. Herein, we prepared a system for PDT using hemoglobin (Hb)‐linked conjugated polymer nanoparticles (CPNs), which can luminesce and supply oxygen. Hb catalyzes the activation of luminol, the conjugated polymer poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH–PPV) nanoparticles can absorb the chemiluminescence of luminol through chemiluminescence resonance energy transfer (CRET) and then sensitize the oxygen supplied by Hb to produce reactive oxygen species that kill cancer cells. This system could be used for the controlled release of an anticancer prodrug. The system does not need an external light source and circumvents the insufficient level molecular oxygen under hypoxia. This work provides a proof‐of‐concept to explore smart and multifunctional nanoplatforms for phototherapy.     

Luminescent,Oxygen‐Supplying,Hemoglobin‐Linked Conjugated Polymer Nanoparticles for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising method for cancer treatment. Two parameters that influence the efficacy of PDT are the light source and oxygen supply. Herein, we prepared a system for PDT using hemoglobin (Hb)‐linked conjugated polymer nanoparticles (CPNs), which can luminesce and supply oxygen. Hb catalyzes the activation of luminol, the conjugated polymer poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH–PPV) nanoparticles can absorb the chemiluminescence of luminol through chemiluminescence resonance energy transfer (CRET) and then sensitize the oxygen supplied by Hb to produce reactive oxygen species that kill cancer cells. This system could be used for the controlled release of an anticancer prodrug. The system does not need an external light source and circumvents the insufficient level molecular oxygen under hypoxia. This work provides a proof‐of‐concept to explore smart and multifunctional nanoplatforms for phototherapy.     

Direct Photocontrol of Peptidomimetics: An Alternative to Oxygen‐Dependent Photodynamic Cancer Therapy

Conventional photodynamic treatment strategies are based on the principle of activating molecular oxygen in situ by light, mediated by a photosensitizer, which leads to the generation of reactive oxygen species and thereby causes cell death. A diarylethene‐derived peptidomimetic is presented that is suitable for photodynamic cancer therapy without any involvement of oxygen. This light‐sensitive molecule is not a mediator but is itself the cytotoxic agent. As a derivative of the cyclic amphiphilic peptide gramicidin S, the peptidomimetic exists in two thermally stable photoforms that are interconvertible by light of different wavelengths. The isomer generated by visible light shows much stronger toxicity against tumor cells than the UV‐generated isomer. First in vivo applications are demonstrated on a tumor animal model to illustrate how the peptidomimetic can be administered in the less toxic form and then activated locally in a solid tumor by visible light.