The ultra-photostable and electrically modulated Stimulated Emission in perylene-based dye doped liquid crystal

Effect of Different Substitutions at the 1,7-Bay Positions of Perylenediimide Dyes on Their Optical and Laser Properties

Perylenediimide (PDI) compounds are widely used as the active units of thin-film organic lasers. Lately, PDIs bearing two sterically hindering diphenylphenoxy groups at the 1,7-bay positions have received attention because they provide a way to red-shift the emission with respect to bay-unsubstituted PDIs, while maintaining a good amplified spontaneous emission (ASE) performance at high doping rates. Here, we report the synthesis of a series of six PDI derivatives with different aryloxy groups (PDI 6 to PDI 10) or ethoxy groups (PDI 11) at the 1,7 positions of the PDI core, together with a complete characterization of their optical properties, including absorption, photoluminescence, and ASE. We aim to stablish structure-property relationships that help designing compounds with optimized ASE performance. Film experiments were accomplished at low PDI concentrations in the film, to resemble the isolated molecule behaviour, and at a range of increasing doping rates, to investigate concentration quenching effects. Compounds PDI 10 and PDI 7, bearing substituents in the 2' positions of the benzene ring (the one contiguous to the linking oxygen atom) attached to the 1,7 positions of the PDI core, have shown a better threshold performance, which is attributed to conformational (steric) effects. Films containing PDI 11 show dual ASE.

Dye spectra of benzene derivatives in the liquid-crystalline phase of 4-n-pentyl-4΄-cyanobiphenyl

In the present paper, we study the interaction of associates (dimers and trimers) of 4-n-pentyl-4΄-cyanobiphenyl (5CB) with 1, 2-Diamino-4-nitrobenzene and N, N-Dimethyl-4-nitrosoaniline dye molecules. The structures of the intermolecular complexes were studied using hybrid functionals of the DFT method M06 and B3LYP with the 6-31 + G (d) basis set. The intermolecular binding energy of dyes with associates depends on the structure of the complexes and is about 5 kcal/mol. Vibrational spectra were calculated for all intermolecular systems. The electronic absorption spectra of dyes are sensitive to the structure of the mesophase. The pattern of the spectrum changes depending on the structure of the complex of the dimer or trimer with the dye molecule. The long-wavelength transition bands are characterized by shifts that are bathochromic for 1, 2-Diamino-4-nitrobenzene and hypsochromic for N, N-Dimethyl-4-nitrosoaniline.

Perylene-Based Chromophore as a Versatile Dye for Light Amplification

One of the challenges for modern optoelectronics is to find versatile, easily adaptable components for novel laser-based technologies. A very attractive perylene-derivative chromophore in different organic matrices for high-performance light amplification is discussed and outlined. Our approach demonstrates the outstandingly compatible laser dye and a viable strategy to provide an effective optical gain for stimulated emission enhancement. Through structural control, we produce simple optical devices embedded in organic matrices, such as poly(methyl methacrylate), nematic liquid crystalline (NLC) mixture, and a hybrid emulsion system (poly(vinyl alcohol) PVA + NLC mesophase). Importantly, we investigate and compare the spectroscopy of differently constructed organic systems in terms of stimulated-emission thresholds and light amplification process efficiency. Moreover, we report the effects of tunability for LC cells by an applied external electric field stimulus. Future directions of laser systems are outlined with an emphasis on the role of the perylene derivative. The studies meet current challenges in the field of modern organic technologies dedicated to various optoelectronic systems, including touch screens, displays, and Li-Fi networks.

Synergistic effects of side-functionalization and aza-substitution on the charge transport and optical properties of perylene-based organic materials: a DFT study

The physicochemical properties of organic materials are subject to the chemical structure of the molecular unit and the arrangement of molecules in a crystal.

Photoactivated Refractive Index Anisotropy in Fluorescent Thiophene Derivatives

The optical control of anisotropy in materials is highly advantageous for many technological applications, including the real-time modulation of another light signal in photonic switches and sensors. Here, we introduce three thiophene derivatives with a donor-acceptor structure, which feature different positions of an electron-acceptor nitrile group, and both photoalignment and luminescence properties. Quantum chemical calculations highlight the presence of trans-forms stable at room temperature and metastable cis-isomers. Besides photoluminescence peaked at 440-460 nm and 0.4 ns lifetime, the three nonlinear optical chromophores exhibit photoinduced anisotropy of the refractive index closely depending on the specific molecular structure, with higher values of birefringence at lower driving signal being obtained for ortho substitution of the nitrile group. All-optical modulation of an external light beam at rates of hundreds of hertz is demonstrated in the fluorescent systems. This finding opens an interesting route to multispectral photonic switches embedded in the active layers of light-emitting devices.

Photobleaching of organic fluorophores: quantitative characterization, mechanisms, protection

Photochemical stability is one of the most important parameters that determine the usefulness of organic dyes in different applications. This Review addresses key factors that determine the dye photostability. It is shown that photodegradation can follow different oxygen-dependent and oxygen-independent mechanisms and may involve both ¹S₁-³T₁ and higher-energy ¹S_n-³T_n excited states. Their involvement and contribution depends on dye structure, medium conditions, irradiation power. Fluorescein, rhodamine, BODIPY and cyanine dyes, as well as conjugated polymers are discussed as selected examples illustrating photobleaching mechanisms. The strategies for modulating and improving the photostability are overviewed. They include the improvement of fluorophore design, particularly by attaching protective and anti-fading groups, creating proper medium conditions in liquid, solid and nanoscale environments. The special conditions for biological labeling, sensing and imaging are outlined.

Electrically controlled white laser emission through liquid crystal/polymer multiphases

White lasers are becoming increasingly relevant in various fields since they exhibit unprecedented properties in terms of beam brightness and intensity modulation. Here we introduce a white laser based on a polymer matrix encompassing liquid crystals and multiple organic chromophores in a multifunctional phase-separation system. The separation of the hydrophilic matrix and the hydrophobic liquid crystals leads to the formation of a complex optically active layer, featuring lasing emission tuneable from blue to red. White laser emission is found with an optical excitation threshold of approximately 12 mJ/cm2. Importantly, an external electric field can be used to control the device emission intensity. White lasers with low-voltage (≤10 V) controllable emission might pave the way for a new generation of broadband light sources for analytical, computational, and communication applications.

Towards Efficient and Photostable Red-Emitting Photonic Materials Based on Symmetric All-BODIPY-Triads, -Pentads, and -Hexads

The development of efficient and stable red and near-IR emitting materials under hard radiation doses and/or prolonged times is a sought-after task due to their widespread applications in optoelectronics and biophotonics. To this aim, novel symmetric all-BODIPY-triads, -pentads, and -hexads have been designed and synthesized as light-harvesting arrays. These photonic materials are spectrally active in the 655-730 nm region and display high molar absorption across UV-visible region. Furthermore, they provide, to the best of our knowledge, the highest lasing efficiency (up to 68 %) and the highest photostability (tolerance >1300 GJ mol^-1 ) in the near-IR spectral region ever recorded under drastic pumping conditions. Additionally, the modular synthetic strategy to access the cassettes allows the systematic study of their photonic behavior related to structural factors. Collectively, the outstanding behavior of these multichromophoric photonic materials provides the keystone for engineering multifunctional systems to expedite the next generation of effective red optical materials.