Chiral Perylene Bisimide–Melamine Assemblies: Hydrogen Bond‐Directed Growth of Helically Stacked Dyes with Chiroptical Properties

Self‐aggregation and hydrogen bond‐directed superstructure formation with a perylene bisimide dye were investigated for melamines bearing two or four alkyl chains. For a melamine with two n‐octadecyl substituents, large micellar aggregates of several hundred nanometers were observed in methylcyclohexane solution by dynamic light scattering. By means of hydrogen bonding these micelles were loaded with various contents of perylene bisimide dyes up to an equimolar amount. Even at low dye contents, islands of strongly aggregated perylene bisimides were formed according to UV‐vis absorption spectroscopy. In a series of melamines functionalized with n‐octadecyl esters of chiral amino acids, no self‐aggregation of the melamines was observed, and the stability of the assemblies with the perylene bisimide dyes showed strong dependence on the melamine substituents. For four melamine–perylene bisimide combinations stable assemblies formed, which exhibited exciton‐coupled circular dichroism (CD) effects for the perylene bisimide absorption bands whose sign is controlled by the stereoisomerism of the respective melamine. While for (S,S)‐melamines a negative Cotton effect was observed, indicating an M‐helical arrangement of the chromophores within the assembly, the (R,R)‐enantiomer induced P‐helicity, and no CD effect was found for the achiral (R,S)‐diastereomer.     

Materials for a Reliable Solid‐State Dye Laser at the Red Spectral Edge

In the search to extend the tuning range of solid‐state dye lasers (SSDLs) to the red‐edge spectral region, new photosensitive materials have been designed and synthesized based on six commercial dyes (sulforhodamine B, perylene red, rhodamine 640, LDS698, LDS722, and LDS730) incorporated into different linear, crosslinked, fluorinated, and sililated polymeric matrices. Under transversal pumping at 532 nm, these materials exhibit highly efficient, stable, as well as wavelength‐tunable laser action from the visible‐to‐NIR spectral region (575–750 nm). The lasing performance of the materials doped with perylene and xanthene dyes is, to the best of our knowledge, the highest achieved to date for these chromophores when incorporated into organic, inorganic, or hybrid matrices. Regarding the LDS derivatives, this is the first time that laser action from these dyes in solid‐state media is reported. These particular characteristics have impelled the building of the first prototype SSDL that is compact, versatile, and easy to handle.     

Carboxylates versus Fluorines: Boosting the Emission Properties of Commercial BODIPYs in Liquid and Solid Media

A new and facile strategy for the development of photonic materials is presented that fufills the conditions of being efficient, stable, and tunable laser emitters over the visible region of spectrum, with the possibility of being easily processable and cost‐effective. This approach uses poly(methyl methacrylate) (PMMA) as a host for new dyes with improved efficiency and photostability synthesized. Using a simple protocol, fluorine atoms in the commercial (4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene) (F‐BODIPY) by carboxylate groups. The new O‐BODIPYs exhibit enhanced optical properties and laser behavior both in the liquid and solid phases compared to their commercial analogues. Lasing efficiencies up to 2.6 times higher than those recorded for the commercial dyes are registered with high photostabilities since the laser output remain at 80% of the initial value after 100 000 pump pulses in the same position of the sample at a repetition rate of 30 Hz; the corresponding commercial dye entirely loses its laser action after only 12 000 pump pulses. Distributed feedback laser emission is demonstrated with organic films incorporating new O‐BODIPYs deposited onto quartz substrates engraved with appropriated periodical structures. These dyes exhibit laser thresholds up to two times lower than those of the corresponding parent dyes with lasing intensities up to one order of magnitude higher.     

The preparation of BiOCl photocatalyst and its performance of photodegradation on dyes

The photocatalyst BiOCl was prepared by a facile hydrolysis method and employed to study the phase structure, morphology and optical properties via X-ray diffraction, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of BiOCl was tested on the degradation of the selected four kinds of dyes under UV and visible light irradiation. The results showed that four dyes molecules could be efficiently degraded over BiOCl under UV light irradiation. Most of all, rhodamine B was thoroughly degraded after visible light irradiation in 60 min and this was ascribed to the dye photosensitization mechanism. The decomposition efficiency of RhB was apparently reduced by adding silver nitrate solution to capture electron of the LUMO orbit. This study demonstrated that electron of the LUMO level of dye molecules played an important role in the dye photosensitization reaction.     

Comparative Studies on Optical,Redox, and Photovoltaic Properties of a Series of D–A–D and Analogous D–A Chromophores

A series of new symmetrical donor‐acceptor‐donor (D?A?D) dyes based on s‐indacene‐1,3,5,7(2H,6H)‐tetraone as an acceptor unit containing varying electron donating moieties and analogous donor‐acceptor (D?A) chromophores with indane‐1,3‐dione as an acceptor are synthesized. By employing these two sets of dyes, the influence of a scaffold change from unsymmetric push‐pull (D?A) to symmetrical (D?A?D) systems on optical, electrochemical, and photovoltaic properties are explored. Detailed comparative studies reveal favorable optical characteristics and considerably decreased bandgaps for the D?A?D dyes compared to those of the reference D?A chromophores. Accordingly, the evaluation of the present dyes as donor materials in bulk heterojunction (BHJ) solar cells in combination with fullerene derivatives PC₆₁BM or PC₇₁BM as acceptors afforded significantly improved performance for devices based on D?A?D blends (up to a factor of 4 compared to the respective D‐A reference) with power conversion efficiencies of up to 2.8%. In less polar solvents such as toluene, some of the novel D?A?D chromophores exhibit unexpectedly high fluorescence quantum yields Φ_em of up to unity, in striking contrast to their weakly fluorescent D‐A counterparts.     

Novel Conjugated Organic Dyes for Efficient Dye‐Sensitized Solar Cells

Novel conjugated organic dyes that have N,N‐dimethylaniline (DMA) moieties as the electron donor and a cyanoacetic acid (CAA) moiety as the electron acceptor were developed for use in dye‐sensitized nanocrystalline‐TiO₂ solar cells (DSSCs). We attained a maximum solar‐energy‐to‐electricity conversion efficiency (η) of 6.8 % under AM 1.5 irradiation (100 mW cm^–2) with a DSSC based on 2‐cyano‐7,7‐bis(4‐dimethylamino‐phenyl)hepta‐2,4,6‐trienoic acid (NKX‐2569): short‐circuit photocurrent density (J_sc) = 12.9 mA cm^–2, open‐circuit voltage (V_oc) = 0.71 V, and fill factor (ff) = 0.74. The high performance of the solar cells indicated that highly efficient electron injection from the excited dyes to the conduction band of TiO₂ occurred. The experimental and calculated Fourier‐transform infrared (FT‐IR) absorption spectra clearly showed that these dyes were adsorbed on the TiO₂ surface with the carboxylate coordination form. A molecular‐orbital calculation indicated that the electron distribution moved from the DMA moiety to the CAA moiety by photoexcitation of the dye.     

Hydrophobic Chromophores in Aqueous Micellar Solution Showing Large Two‐Photon Absorption Cross Sections

A series of new hydrophobic two‐photon absorbing (2PA) chromophores with varied electron‐donating groups in quasi‐linear and multibranched structures are synthesized to correlate their structure/photophysical property relationships. The feasibility of using these large two‐photon absorption cross‐sectional (δ, expressed in GM = 1 × 10^–50 cm⁴ s photon^–1 molecule^–1) materials in aqueous solution is also explored. All four hydrophobic 2PA materials can be encapsulated into micelles generated by dispersing an amphiphilic block copolymer, poly(methacrylic acid)‐block‐polystyrene (PMAA‐b‐PS), into water. The micellar nanostructures are characterized using dynamic light scattering, atomic force microscopy, and transmission electron microscopy. After these dyes are incorporated into micelles, they exhibit strong fluorescence in water. It is found that the quantum yield and δ values of these chromophores are strongly dependent on the diameters of the micelles, concentrations of the PMAA‐b‐PS, and molecular structures of the 2PA chromophores. One of the compounds that has a strong triarylamino donor and a multibranched structure exhibits a large δ value of 2790 GM and high quantum yield (0.56) in micelle‐containing water. Although this value is smaller than the original value of 5300 GM in toluene, it is still substantially larger than the values of most water‐soluble 2PA materials, which have δ values of less than 100 GM.     

Synthesis and Properties of Photoisomerizable Derivatives of Isosorbide and Their Use in Cholesteric Filters

This paper describes the synthesis of photoisomerizable derivatives of isosorbide. These derivatives contain a stilbene or cinnamate moiety and can therefore be used as photoisomerizable chiral compounds in cholesteric liquid‐crystalline mixtures. The reflection wavelength of cholesteric layers made from these mixtures is increased by UV irradiation due to the fact that the Z‐isomers of these derivatives exhibit a lower helical twisting power than the corresponding E‐isomers. The cinnamate derivatives are very suitable for use in cholesteric color filters that find application in liquid‐crystal displays.     

New Organic Nonlinear Optical Polyene Crystals and Their Unusual Phase Transitions

A series of new nonlinear optical chromophores based on configurationally locked polyenes (CLPs) with chiral pyrrolidine donors are synthesized. All CLP derivatives exhibit high thermal stability with decomposition temperatures T_d at least > 270 °C. Acentric single crystals of enantiopure D ‐ and L ‐prolinol‐based chromophores with a monoclinic space group P2₁ exhibit a macroscopic second‐order nonlinearity that is twice as large than that of analogous dimethylamino‐based crystal. This is attributed to a strong hydrogen‐bonded polar polymer‐like chain built by these molecules, which is aligned along the polar crystallographic b‐axis. Five α‐phase CLP crystals with different donors grown from solution exhibit a reversible or irreversible thermally induced structural phase transition to a β‐phase. These phase transitions are unusual, changing the crystal symmetry from higher to lower at increasing temperatures, for example, from centrosymmetric to non‐centrosymmetric, enhancing their macroscopic second‐order nonlinear optical properties.     

Control of Solid‐State Dye‐Sensitized Solar Cell Performance by Block‐Copolymer‐Directed TiO2 Synthesis

Hybrid dye‐sensitized solar cells are typically composed of mesoporous titania (TiO₂), light‐harvesting dyes, and organic molecular hole‐transporters. Correctly matching the electronic properties of the materials is critical to ensure efficient device operation. In this study, TiO₂ is synthesized in a well‐defined morphological confinement that arises from the self‐assembly of a diblock copolymer—poly(isoprene‐b‐ethylene oxide) (PI‐b‐PEO). The crystallization environment, tuned by the inorganic (TiO₂ mass) to organic (polymer) ratio, is shown to be a decisive factor in determining the distribution of sub‐bandgap electronic states and the associated electronic function in solid‐state dye‐sensitized solar cells. Interestingly, the tuning of the sub‐bandgap states does not appear to strongly influence the charge transport and recombination in the devices. However, increasing the depth and breadth of the density of sub‐bandgap states correlates well with an increase in photocurrent generation, suggesting that a high density of these sub‐bandgap states is critical for efficient photo‐induced electron transfer and charge separation.     

A New Series of Quadrupolar Type Two‐Photon Absorption Chromophores Bearing 11, 12‐Dibutoxydibenzo[a,c]‐phenazine Bridged Amines; Their Applications in Two‐Photon Fluorescence Imaging and Two‐Photon Photodynamic Therapy

A new series of quadrupolar type two‐photon absorption (2PA) chromophores 3 – 9 bearing a core arylamine‐[a,c]phenazine‐arylamine motif are synthesized in high yields. Palladium‐catalyzed Stille coupling and C? N coupling reactions are utilized to prepare target chromophores. Detailed characterization and systematic studies of these molecules, including absorption and fluorescence emission, are conducted. These compounds are found to exhibit very large 2PA cross section values, for example, ～7000 GM at 800 nm for 8 in toluene. Two‐photon‐induced fluorescence imaging is successfully demonstrated in vitro using compound‐ 8 ‐encapsulated silica nanoparticles with excellent bio‐compatibility. In combination with the capability of both one‐ and two‐photon singlet‐oxygen sensitizations, this nanocomposite demonstrates its promising potential in dual functionality toward two‐photon fluorescence imaging and two‐photon photodynamic therapy.     

Poled Sol–Gel Materials With Heterocycle Push–Pull Chromophores that Confer Enhanced Second‐Order Optical Nonlinearity

Hybrid organic–inorganic materials doped with zwitterionic push–pull chromophores with high hyperpolarizability have been synthesized by a sol–gel procedure. A large chromophore concentration was reached by using N‐(hydroxyethyl)carbazole as a physical spacer (preventing the dye aggregation). Spin‐coated doped films were electrically poled and second harmonic generation measurements performed in situ. During the thermally assisted poling under a N₂ atmosphere, only the carbazole molecules degraded. Second‐harmonic generation measurements gave an estimation of the nonlinear coefficient, r₃₃, of 38 pm V^–1 at 1064 nm.     

Squaraine‐Doped Functional Nanoprobes: Lipophilically Protected Near‐Infrared Fluorescence for Bioimaging

Hydrophobically stabilized near‐IR fluorescence from self‐assembled nanoprobes composed of amphiphilic poly(maleic anhydride‐alt‐octadec‐1‐ene) (PMAO) and lipophilized squaraine dopants is reported. From comparative studies with varying lipophilicity of squaraine dyes as well as of nanoparticulate polymer matrices, it is found that dual protection by simultaneous lipophilization of the dye‐polymer pair greatly improves the chemical stability of labile squaraine dyes, to produce efficient NIR fluorescence in physiological aqueous milieux. The surface properties of negatively charged PMAO nanoparticles are readily modified by coating with an amine‐rich cationic glycol chitosan with biofunctionality. Efficient cellular imaging and in vivo sentinel lymph node mapping with size and surface‐controlled nanoprobes demonstrate that lipophilic dual protection of NIR fluorescence and the underlying functional nanoprobe approach hold great potential for bioimaging applications.     

Nano sized ZnO composites: Preparation,characterization and application as photocatalysts for degradation of AB92 azo dye

ZnO and Mordenite zeolite (MOR) nanoparticles were prepared by precipitation process using ultrasonic irradiation and hydrothermal method, respectively. Supported ZnO catalysts were prepared and the effect of different supports on the photocatalytic activity of ZnO nanoparticles was investigated. All prepared samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform-Infra Red Spectroscopy (FTIR), UV–vis spectroscopy (UV–vis) and BET surface area technique. The photocatalytic activity of the synthesized catalysts was elucidated using the photo-oxidation of Acid Blue 92 (AB92) as a hazardous pollutant under UV light. The effect of different parameters such as catalyst concentration, initial dye concentration, pH, UV irradiation and amount of ZnO loaded on the nanocomposites have been examined on the yield and the rate of photocatalytic degradation process. The photodegradation results of AB92 in aqueous medium under UV irradiation revealed that nanocomposite of ZnO and mordenite zeolite exhibit much higher photocatalytic activity than the other nanocomposites and pure ZnO. It was found that the type of support plays an important role in photocatalytic oxidation of AB92 and significantly improved the photocatalytic activity of ZnO. Chemical Oxygen Demand (COD) for dye solutions were examined at regular intervals and gave a good idea about mineralization of the dye.     

Photopatternable Reflective Films Produced by Nanolayer Extrusion

Novel patternable, light‐reflecting multilayer polymer films are presented. The investigated elements comprise 1024 nanolayers of two different, transparent polymers in strictly alternating fashion. Polymers with different refractive indices were employed and the individual layer thickness was controlled between 50 and 200 nm; as a result the investigated films exhibit pronounced optical interference effects. Different photoreactive additives were integrated into the multilayer films, rendering the optical characteristics of these elements tunable. One approach relied on the use of photoreactive blends of poly(methyl methacrylate) (PMMA) and up to 25 wt.‐% of trans‐cinnamic acid (CA) or trans‐methyl cinnamate (MC). Upon exposure to ultraviolet (UV) radiation, CA and MC undergo dimerization through 2+2 cycloaddition, leading to a significant decrease of the blend's refractive index. As a result, the reflectivity of the multilayer films based on these photoreactive blends changes considerably upon photoreaction. The second approach was based on the use of blends of PMMA and 2‐(2′‐benzoylphenyl)benzoxazole (BzPO), a ‘caged’ photoluminescent dye. This benzoyl ester of 2‐(2′‐hydroxyphenyl)benzoxazole (HPBO) is not photoluminescent, but upon exposure to appropriate UV radiation, the ester bond is cleaved, and the photoluminescent HPBO is quantitatively restored. Thus, using conventional photolithographic techniques, reflective multilayer films were patterned with photoluminescent designs.     

Synthesis,Characterization, Two‐Photon Absorption,and Optical Limiting Properties of Ladder‐Type Oligo‐p‐phenylene‐Cored Chromophores

This paper reports on the two‐photon absorption (TPA) and related up‐converted emission properties of a novel series of chromophores containing ladder‐type oligo‐p‐phenylenes with various π‐conjugation lengths. The design and synthesis of these ladder‐type two‐photon chromophores are first discussed. An increase in the π‐conjugated length of the ladder‐type oligo‐p‐phenylene for these chromophores leads to an increase in TPA cross‐section together with an increased fluorescence quantum yield. These chromophores exhibit high fluorescence quantum yields because of the rigid planar structure of the ladder‐type oligomers. The chromophore with an enhanced TPA cross‐section together with an increased fluorescence quantum yield would provide significant benefits for two‐photon excited fluorescence based applications. An improved optical limiting behavior was also demonstrated using the ladder‐type pentaphenylene cored chromophore.     

Light‐Triggered Self‐Assembly of a Spiropyran‐Functionalized Dendron into Nano‐/Micrometer‐Sized Particles and Photoresponsive Organogel with Switchable Fluorescence

The synthesis, self‐assembly, and spectroscopic investigations of spiropyran (SP)‐functionalized dendron 1 are reported. Under UV light irradiation, assembly of 1 into nano‐/microparticles occurs due to the transformation of the closed form of SP into the open merocyanine (MC) form. The formation of these nano‐/microparticles is confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) experiments in addition to the confocal laser scanning microscopy (CLSM) measurements. These nano‐/microparticles exhibit relatively strong red emission. It is interesting to note that the direct cooling of the toluene/benzene solution of 1 to 0 °C leads to gel formation. Multivalent π–π interactions due to the dendron in 1 may be the driving‐force for the gelation. The UV light irradiation cannot destroy the gel phase, and in fact, the gel–gel transition is successfully realized. The purple‐blue gel exhibits relatively strong red fluorescence; moreover, the fluorescence can be reversibly switched by alternating UV and visible light irradiation. The results clearly indicate that the MC form after aggregation becomes more stable and fluorescent.     

Photoswitchable Gas Permeation Membranes Based on Liquid Crystals

We have fabricated switchable gas permeation membranes in which a photoswitchable low‐molecular‐weight liquid crystalline (LC) material acts as the active element. Liquid crystal mixtures are doped with mesogenic azo dyes and infused into commercially available track‐etched membranes with regular cylindrical pores (0.40 to 10.0 μm). Tunability of mass transfer can be achieved through a combination of (1) LC/mesogenic dye composition, (2) surface‐induced alignment, and (3) reversible photoinduced LC‐isotropic transitions. Photo‐induced isothermal phase changes in the imbibed material afford large and fully reversible changes in the permeability of the membrane to nitrogen. Both the LC and photogenerated isotropic states demonstrate a linear permeability/pressure relationship, but they show significant differences in their permeability coefficients. Liquid crystal compositions can be chosen such that the LC phase is more permeable than the isotropic—or vice versa – and can be further tuned by surface alignment. Permeability switching response times are 5 s, with alternating UV and >420‐nm radiation at an intensity of 2 mW/cm² being sufficient for complete and reversible switching. Thermal and kinetic properties of the confined LC materials are evaluated and correlated with the observed permeation properties. We demonstrate for the first time reversible permeation control of a membrane with light irradiation.     

Light‐Controlled Reversible Manipulation of Microgel Particle Size Using Azobenzene‐Containing Surfactant

The light‐induced reversible switching of the swelling of microgel particles triggered by photo‐isomerization and binding/unbinding of a photosensitive azobenzene‐containing surfactant is reported. The interactions between the microgel (N‐isopropylacrylamide, co‐monomer: allyl acetic acid, crosslinker: N,N′‐methylenebisacrylamide) and the surfactant are studied by UV‐Vis spectroscopy, dynamic and electrophoretic light scattering measurements. Addition of the surfactant above a critical concentration leads to contraction/collapse of the microgel. UV light irradiation results in trans‐cis isomerization of the azobenzene unit incorporated into the surfactant tail and causes an unbinding of the more hydrophilic cis isomer from the microgel and its reversible swelling. The reversible contraction can be realized by blue light irradiation that transfers the surfactant back to the more hydrophobic trans conformation, in which it binds to the microgel. The phase diagram of the surfactant‐microgel interaction and transitions (aggregation, contraction, and precipitation) is constructed and allows prediction of changes in the system when the concentration of one or both components is varied. Remote and reversible switching between different states can be realized by either UV or visible light irradiation.     

Organic Dye Graphene Hybrid Structures with Spectral Color Selectivity

This study characterizes a hybrid structure formed between graphene and organic dye molecules for use in photodetectors with spectral color selectivity. Rhodamine‐based organic dye molecules with red, green, or blue light absorption profiles are deposited onto a graphene surface by dip‐coating. UV–vis absorption spectroscopy, charge transport measurements, and density functional theory based calculations reveal that the photoresponses of the dye graphene hybrid films are governed by the light absorption of the dye molecules and also by the photo‐excited‐charge‐transfer‐induced photocurrent gain. The hybrid films respond only to photons with an energy exceeding the band gap of the immobilized dye. Dye‐Graphene charge transfer is affected by the distance and direction of the dipole moment between the two layers. The resulting hybrid films exhibit spectral color selectivities with responsivities of ≈10³ A W^?1 and specific detectivities of ≈10¹⁰ Jones. This study demonstrates the successful operation of photodetectors with a full‐color optical bandwidth using hybrid graphene structures coated with a mixture of dyes. The strategy of building a simple hybrid photodetector can further offer many opportunities to be also tuned for other optical functionalities using a variety of commercially available dye molecules.