Optical Properties In Solution Research Articles

D-π-A chromophores based on novel macroacceptors - Fused (azinylmethylene)malononitriles: Linear and nonlinear optical properties in solution and in poled polymer films

D-π-A chromophores based on novel macroacceptors − fused azinylmethylenemalononitriles (fused azine = pyrido [2,3-b]pyrazine, quinoline, quinoxaline and quinoxalin-2-one) − have been synthesized and their linear and nonlinear optical properties in gas, solution and in poled PMMA-based films have been investigated by DFT, UV–vis and second harmonic generation technique. The transition from chromophores with an azine acceptor to ones with azinylmethylenemalononitrile acceptors leads to a 10-fold increase in calculated μβ values. Poled polymer films doped with studied chromophores at 25 wt% load exhibit quadratic nonlinear optical activity with d33 values up to 42 pm/V.

Development of D-π-A organic dyes for discriminating HSA from BSA and study on dye-HSA interaction

HSA (human serum albumin), a most abundant protein in blood serum, plays a key role in maintaining human health. Abnormal HSA level is correlated with many diseases, and thus has been used as an essential biomarker for therapeutic monitoring and biomedical diagnosis. Development of small-molecule fluorescent probes allowing the selective and sensitive recognition of HSA in in vitro and in vivo is of fundamental importance in basic biological research as well as medical diagnosis. Herein, we reported a series of new synthesized fluorescent dyes containing D-π-A constitution, which exhibited different optical properties in solution and solid state. Among them, dye M−H−SO3 with a hydrophilic sulfonate group at electron-acceptor part displayed selectivity for discrimination of HSA from BSA and other enzymes. Upon binding of dye M−H−SO3 with HSA, a significant fluorescence enhancement with a turn-on ratio about 96-fold was triggered. The detection limit was estimated to be ∼ 40 nM. Studies on the interaction mechanism revealed that dye M−H−SO3 could bind to site III of HSA with a 1:1 binding stoichiometry. Furthermore, dye M−H−SO3 has been applied to determine HSA in real urine samples with good recoveries, which provided a useful method for HSA analysis in biological fluids.

Chemical and thermal stability of novel phenyl-BODIPY symmetric dimer thin films

Phenyl-BODIPY-dimers are an increasingly interesting motif whose unique electronic and morphological properties make them excellent candidates for a wide range of applications in materials chemistry, including device design and fabrication. Two dimers based on the meso‑(4-ethynylphenyl)-BODIPY unit were obtained through sequential Sonogashira and Glaser-Hay-type coupling reactions. The synthesized compounds, present a significant advantage in terms of solution stability compared to their monomers. An evaluation of their properties, both in solution and thin films, highlights that these dimers maintain exceptional chemical and structural stability when deposited in films, suggesting their plausible use in coatings and devices. The studied dimers exhibit reduced wettability given their surface roughness, meaning a potential for varied applications. Finally, a tandem analysis that included UV–Vis/fluorescence measurements and quantum chemistry methods was carried out to analyze the optical properties in solution and solid-state helping to gain insight into the optical properties of the synthesized molecules and the effect of π-interacting solvents.

A novel central seven-membered BOPYOs: Synthesis, optical properities and optimization of BF2 removal

Many efforts have been made to enrich the variety of BF2 complexes because of their excellent optical properties. However, the investigation on seven-membered ring N, O-chelated BF2 complexes is rare due to their instability with the removal of BF2 unit. Herein, a novel seven-membered ring N, O-chelated BF2 complexes (BOPYOs) with dual-state emission has been synthesized via a facile method. The results of optical properties showed that the fluorescence quantum yield of BOPYO-2 with donor group on 1 and 2-position of 1-indanone unit is much higher than that of BOPYO-1, 3–5 in toluene. The emission spectra of BOPYO-6 or 7 have redshift phenomenon compared with BOPYO-1–5 with weak fluorescence intensity due to their highly distorted structure or intramolecular charge transfer (ICT) effect. BOPYOs show relatively moderate solid emission from orange to deep red color with 596 nm to 686 nm. On the contrary, fluorescence quantum yield of BOPYO-2 in solid is the lowest. The optical properties in solution and solid states are further supported by the single-crystal structure and DFT calculation. Furthermore, the investigation on optimization of BF2 removal shows that the corresponding precursors of BOPYOs could be obtained in protic solvents without adding other catalysts.

Photophysics of Conjugated Oligoelectrolytes Relevant to Two‐Photon Fluorescence‐Lifetime Imaging Microscopy

AbstractConjugated oligoelectrolytes (COEs) comprise a class of cell‐membrane intercalating molecules that serve as effective optical reporters. However, little is known about the photophysical properties of COEs in biological environments such as buffers, cell membranes, and intracellular organelles, which is critical to optimize performance. Herein, how COE self‐assembly depends on the dielectric environment (polarity and ion content) is explored based on the representative molecule 6‐ring phenylenevinylene (PV) conjugated oligoelectrolyte (COE‐S6), and its optical properties within mammalian cells are subsequently studied. Two‐photon fluorescence lifetime imaging microscopy (FLIM), confocal laser scanning microscopy, and optical properties in solutions are brought together to obtain information about the location, accumulation, and characteristics of the local surroundings. FLIM imaging lifetime phasor plots, decays, and fluorescence spectra on stained mammalian cells provide evidence of successful COE‐S6 internalization via endocytosis. The fluorescence lifetime of COE‐S6 is identical when in A549 mammalian cells and in giant unilamellar vesicle model membranes, thereby providing a correlation between living system and artificial constructs.

Amphiphilic Near‐Infrared Fluorescent Molecular Probes: Optical Properties in Solution and in Surfactant Micelle Microenvironment

AbstractIn this work, the optical properties of two novel near‐infrared fluorescent tricarbocyanines with amphiphilic nature, CyN and CyS, were studied in solution and in micelles of representative surfactants (anionic, cationic and non‐ionic) by means of spectroscopic techniques. Interestingly, the spectral properties of the new fluorophores depend on the nature of the heteroatom at the meso position. Dependence on the solvent polarity and the viscosity were also observed in both cases. Furthermore, changes on photophysical properties occurred upon encapsulation of the dyes. The incorporation of the dye from the aqueous solution to the surfactant supramolecular assembly produced a drastic change in the fluorescence emission from quenched state to fluorescence enhancement, rendering an OFF‐ON response to the exchange of environment. In addition, a significant protective effect against photobleaching was determined when the dyes were included in Pluronic® micelles (F127) resulting in a promising system to be used as a fluorescent nanosized container. The novel amphiphilic NIR fluorophores also interact as a Förster resonance energy transfer (FRET) pair and the process was studied within micelles loaded with both dyes.

Synthesis and Properties of Stable Amino Metal Halide Molecular Clusters in the Solid State.

Nanosized molecular clusters (MCs) composed of PbBr2 and neutral ligand butylamine (BTYA) with unique optical properties in solution and solid states have been synthesized using ligand-assisted reprecipitation and spin-coating, separately. The studies of their optical properties using ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) show the first electronic absorption and PL band of the MCs at 401 and 411 nm, respectively, for the solution and solid state samples that exhibit good stability under ambient conditions. Low-temperature PL spectra below 30 K show vibronic peaks indicative of a single size or a very narrow size distribution of the MCs. On the basis of Raman, X-ray diffraction, and transmission electron microscopy measurements, a layered structural model is proposed for the MCs with a BTYA ligand capping on the surface of the corner-shared tilted [PbBr6]4- octahedral framework. The stable and retained structure of MCs in the solid state is promising for photonics applications.

Exploring the optical properties of novel pyridazin-3(2H)-one derivatives - A combined experimental and computational study

• Three pyridazinone derivatives were synthesized and characterized by FT-IR, 1 H-NMR, 13 C-NMR and ESI-MS. • Computational studies were performed by B3LYP/6-31+g(d,p) level. • TD-DFT calculations are adopted to construct theoretical absorption spectra in the solvent phase which is compared with the experiments. • Synthesized compounds were studied for their optical properties in solution and solid phases. Three novel fluorophores i.e. (E)-4-(2-chlorobenzyl)-6-(4-chlorostyryl)pyridazin-3(2H)-one (4a) , (E)-6-(4-chlorostyryl)-4-(4-methoxybenzyl)pyridazin-3(2H)-one (4b) and (E)-4-benzyl-6-(4-chlorostyryl)pyridazin-3(2H)-one (4c) were synthesized and characterized by FT-IR, 1 H-NMR, 13 C-NMR and mass spectrometry . To gain insights into the structure-property relationship, a detailed computational study is taken up here at the B3LYP/6-31+g(d,p) level. Frontier molecular orbital (FMO) analysis and natural bond orbital analysis (NBO) are done on the optimized geometries to evaluate the reactivity and stability of the molecules. Electrostatic potential maps offer the charge distribution in these molecules. Time-dependent density functional theory calculations are adopted to construct theoretical absorption spectra in the solvent phase which is compared with the experiments. In addition, the synthesized compounds were studied for their optical properties in solution and solid phases. Consequently, the fluorophores studied, show emissions, which cover a spectral range, going from 416 nm for compound 4b to 418 nm for 4c and 421nm for compound 4a .

Chasing Self‐Assembly of Thioether‐Substituted Flavylium Salts in Solution and Bulk State

Two series of flavylium triflates carrying alkoxy side chains in the A‐ring (benzo unit of chromylium salt) and thioethers in the B ring (phenyl unit) (On ‐Fla‐Sm ) as well as thioethers at both A and B ring (Sn ‐Fla‐Sm ) were synthesized in order to understand the effect of thioether functionalization on their self‐assembly and electronic properties. Concentration‐dependent and diffusion ordered (DOSY) NMR experiments of O1 ‐iV‐Fla‐S3 indicate the formation of columnar H‐aggregates in solution with antiparallel intracolumnar stacking of the AC unit (chromylium) of the flavylium triflate, in agreement with the solid state structure of O1 ‐V‐Fla‐S1 . Thioether substitution on the B ring changes the linear optical properties in solution, whereas it has no effect on the A ring. According to differential scanning calorimetry, polarizing optical microscopy and X‐ray diffraction bulk self‐assembly of these ionic liquid crystals (ILCs) depends on the total number of side chains, yielding SmA and LamCol phases for ILCs with 2–3 chains and Colro, Colh phases for ILCs with 3–6 chains. Thus, we demonstrated that thioethers are a useful design tool for ILCs with tailored properties.

Boranils: Versatile Multifunctional Organic Fluorophores for Innovative Applications

Multifunctional stimuli-responsive fluorophores showing bright environment-sensitive emissions have fueled intense research due to their innovative applications in the fields of biotechnologies, optoelectronics, and materials. A strong structural diversity is observed among molecular materials, which has been enriched over the years with a growing responsiveness to stimuli. Boron dipyrromethene (BODIPY) dyes have long been the flagship of emissive boron complexes due to their outstanding properties until a decade ago when analogues based on N^O, N^N, or N^C π-conjugated chelates emerged. The finality of developing borate dyes was to compensate for BODIPYs’ lack of solid-state fluorescence and small Stokes shifts while keeping their excellent optical properties in solution. Among them, the borate complexes based on a salicylaldimine ligand, called by the acronym boranils appear as the most promising, owing to their facile synthesis and dual-state emission properties. Boranil dyes have proven to be good alternatives to BODIPY dyes and have been applied in applications such as bioimaging, bioconjugation, and detection of biosubstrates. Meanwhile, ab initio calculations have rationalized experimental results and provided insightful feedback for future designs. This review article aims at providing a concise yet representative overview of the chemistry around the boranil core with the subsequent applications.

Synthesis and Optical Properties of Thiazolo-Chlorin and Porphyrin Skeletons.

Macrocyclic π-skeletons containing a thiazole moiety were synthesized via MacDonald [3 + 1]-type condensation. The construction of thiazolochlorin 1a and thiazoloporphyrin 1b depended on the conformation of the thiazole moieties, and their 18π-systems expanded along the molecular y and x axes, respectively. In particular, the structure of thiazolochlorin 1a was studied in detail using 2D nuclear magnetic resonance methods. The optical properties in solution were measured and discussed based on both experimental data and computational studies.

Stereoisomer-Independent Stable Blue Emission in Axial Chiral Difluorenol.

Bulky conjugated molecules with high stability are the prerequisite for the overall improvement of performance in wide-bandgap semiconductors. Herein, a chiral difluorenol, 2,2′-(9,9′-spirobi[fluorene]-2,2′-diyl)bis(9-(4-(octyloxy)phenyl)-9H-fluoren-9-ol) (DOHSBF), is set as a desirable model to reveal the stereoisomeric effects of wide-bandgap molecules toward controlling photophysical behavior and improving thermal and optical stability. Three diastereomers are obtained and elucidated by NMR spectra. Interestingly, the effect of modifying the stereo-centers is not observed on optical properties in solutions, pristine films, or post-treated film states. All three diastereomers as well as the mixture exhibit excellent spectral stability without undesirable green emission. Therefore, this stereoisomer-independent blue-emitting difluorenol will be a promising candidate for next-generation wide-bandgap semiconductors that would have extensive application in organic photonics.

Influence of the Curing and Annealing Temperatures on the Properties of Solution Processed Tin Oxide Thin Films

We report the effect of the curing (Tcuring) and annealing (Tanneal) temperatures on the structural, electrical, and optical properties of solution processed tin oxide. Tanneal was varied from 300 to 500 °C, and Tcuring from 200 °C to Tanneal. All Tanneal lead to a polycrystalline phase, but the amorphous phase was observed at Tanneal = 300 °C and Tcuring ranging from 250 to 300 °C. This could be explained by the melting point of the precursor (SnCl2), occurring at 250 °C. The crystallinity can be effectively controlled by the annealing temperature, but the curing temperature dramatically affects the grain size. We can reach grain sizes from 5–10 nm (Tcuring = 200 °C and Tanneal = 300 °C) to 30–50 nm (Tcuring = 500 °C and Tanneal = 500 °C). At a fixed Tanneal, Hall mobilities, carrier concentration, and conductivity increased with the curing temperature. The Hall mobility was in the range of 1 to 9.4 cm2/Vs, the carrier concentration was 1018 to 1019 cm−3, and the conductivity could reach ~20 S/cm when the grain size was 30–50 nm. The optical transmittance, the optical bandgap, the refractive index, and the extinction coefficient were also analyzed and they show a correlation with the annealing process.

Mobility of doxorubicin in TPGS micelles in response to sodium taurodeoxycholate incorporation: Analyses based on scattering and fluorescence studies

This study describes the effect of bile salt addition upon encapsulation locus of doxorubicin (DOX, a hydrophilic anticancer drug) in D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) micelles. Sodium taurodeoxycholate (NaTDC) was used as bile salt. After analyzing the scattering behavior of TPGS-NaTDC mixed system, steady-state fluorescence, time-resolved fluorescence and fluorescence anisotropy techniques were employed to track the movement of DOX in micelles at various NaTDC concentrations. Our results suggest that after triggering contraction of micelles in low concentration regime (0.05–0.5 mM), NaTDC molecules participated with TPGS to form mixed micelles (average hydrodynamic diameter: 8–11 nm) and swollen aggregates (200–300 nm). In spite this, no changes in the shape of micelles and optical properties of solution were recorded. Small angle neutron scattering data suggest that NaTDC molecules engaged with core-forming segment of TPGS at low concentration (0.05–1.0 mM), and later migrated towards the shell region and imparted electrostatic charge to the headgroups. Transitions beyond this point (>1.0 mM) were marked by drastic changes in the effective charge of aggregates and aggregation number of participating molecules. We have shown that NaTDC-derived electrostatic charge can be exploited to drive positively charged DOX molecules from the hydrophilic shell to apolar core region in TPGS micelles. Importantly, loaded DOX molecules remained stable against storage time (up to 50 days) and microenvironment temperature (25–40°C).

Distinct Tetracyanoquinodimethane Derivatives: Enhanced Fluorescence in Solutions and Unprecedented Cation Recognition in the Solid State.

Tetracyanoquinodimethane (TCNQ) is known to react with various amines to generate substituted TCNQ derivatives with remarkable optical and nonlinear optical characteristics. The choice of amine plays a crucial role in the outcome of molecular material attributes. Especially, mono/di-substituted TCNQ’s possessing strong fluorescence in solutions than solids are deficient. Furthermore, cation recognition in the solid-state TCNQ derivatives is yet undetermined. In this article, we present solution-enhanced fluorescence and exclusive solid-state recognition of K+ ion achieved through the selection of 4-(4-aminophenyl)morpholin-3-one (APM) having considerable π-conjugation and carbonyl (C=O) functionality, particularly in the ring. TCNQ when reacted with APM, in a single-step reaction, resulted in two well-defined distinct compounds, namely, 7,7-bis(4-(4-aminophenyl)morpholin-3-ono)dicyanoquinodimethane (BAPMDQ [1], yellow) and 7,7,8-(4-(4-aminophenyl)morpholin-3-ono)tricyanoquinodimethane (APMTQ [2], red), with increased fluorescence intensity in solutions than their solids. Crystal structure investigation revealed extensive C–H−π interactions and strong H-bonding in [1], whereas moderate to weak interactions in [2]. Surprisingly, simple mechanical grinding during KBr pellet preparation with [1, 2] triggered unidentified cation recognition with a profound color change (in ∼1 min) detected by the naked eye, accompanied by a drastic enhancement of fluorescence, proposed due to the presence of carbonyl functionality, noncovalent intermolecular interactions, and molecular assemblies in [1, 2] solids. Cation recognition was also noted with various other salts as well (KCl, KI, KSCN, NH4Cl, NH4Br, etc.). Currently, the recognition mechanism of K+ ion in [1, 2] is demonstrated by the strong electrostatic interaction of K+ ion with CO and simultaneously cation−π interaction of K+ with the phenyl ring of APM, supported by experimental and computational studies. Computational analysis also revealed that a strong cation−π interaction occurred between the K+ ion and the phenyl ring (APM) in [2] than in [1] (ΔGbinding calculated as ∼16.3 and ∼25.2 kcal mol–1 for [1] and [2], respectively) providing additional binding free energy. Thus, both electrostatic and cation−π interactions lead to the recognition. Scanning electron microscopy of drop-cast films showed microcrystalline “roses” in [1] and micro/nano “aggregates” in [2]. Optical band gap (∼3.565 eV) indicated [1, 2] as wide-band-gap materials. The current study demonstrates fascinating novel products obtained by single-pot reaction, resulting in contrasting optical properties in solutions and experiencing cation recognition capability exclusively in the solid state.

A sextuple-decker heteroleptic phthalocyanine heterometallic samarium-cadmium complex with crystal structure and nonlinear optical properties in solution and gel glass.

A sextuple-decker heteroleptic phthalocyanine heterometallic compound (1) with a subunit arrangement of {(Pc)Sm(Pc)Cd(Pc*)Cd(Pc*)Cd(Pc)Sm(Pc)} has been prepared and analyzed using various spectroscopic instruments, in which four unsubstituted phthalocyanine anions (Pc) and two substituted analogues (Pc*) with n-pentoxyl substituents at eight peripheral positions are connected through the complexation of two Sm(III) and three Cd(II) ions. In particular, its sextuple-decker structure has been disclosed by the single-crystal X-ray diffraction technique. The solution and gel glass forms of this compound display third-order nonlinear optical properties due to the intrinsic conjugated nature over the sextuple-decker sandwich complex.

Site-selective C20-fluorinations of chlorophyll-a derivatives using N-fluorobenzenesulfonimide and their optical properties

Site-selective fluorinations at the C20 position of methyl pyropheophorbides- a , which is derived from naturally occurring chlorophyll(Chl)- a , were achieved by using N -fluorobenzenesulfonimide (NFSI). All the synthetic Chl- a derivatives possessing a variety of the C3-substituents (vinyl, ethyl, formyl, acetyl, hydroxymethyl, and 1-hydroxyethyl groups) were mono-fluorinated to produce the corresponding 20-fluoro-chlorins as isolated products. These fluorinated products were characterized by 1D/2D NMR, visible absorption, and fluorescence emission spectroscopy. Owing to the strong electronegativity of the C20-fluorine atom, their red-most Qy absorption and fluorescence emission bands were bathochromically shifted except for the C3-acetyl substitutes. This study showed not only tolerance of the chlorin π-skeleton and C3-substituents to NFSI but also potential availability of the fluorinated Chl library. • N -Fuorobenzenesulfonimide was useful for fluorination of chlorophyll- a derivatives. • The fluorination site-selectively occurred at the C20 position of chlorin π-system. • The mild fluorination was performed without modification of the C3-substituents. • The electron-withdrawing C20-F partially affected molecular conformations. • The C20-fluorination specifically changed optical properties in solution.

2,1,3-Benzothiadiazole dyes conjugated with benzothiazole and benzoxazole: Synthesis, solvatochromism and solid-state properties

Benzothiadiazole (BTD) dyes are an important class of N,S-containing heterocycles that have remarkable optical properties. In this work, two new 2,1,3-benzothiadiazole dyes conjugated with benzothiazole and benzoxazole moieties were synthesized and the optical properties in solutions and in the solid state were investigated. The BTD dyes were synthesized in a single step from cyclization of ortho-diamino benzothiazole and ortho-diamino benzoxazole dyes. The photophysical behavior of BTD precursor's benzoxazole and benzothiazole dyes were also investigated. The dyes present absorption in the UVB (280–315 nm) and UVA (315–400 nm) wavelength and fluorescence in the blue-green visible region. The solvatochromic properties of the dyes were investigated in different solvents taking into account the solvent orientation polarizability (Δf) and ET (30) polarity solvent parameter. The ground and excited state dipole moments were determined by applying Bakshiev's and Kawaski-Chamma-Viallet's formulations. Furthermore, the spectroscopic properties of thin films and powders of BTD dyes were explored.

Nucleophilic Substitution Reaction of Pentafluorophenyl Aminated Perylene Diimide system with N,N‐Dimethylformamide

AbstractNucleophilic substitution process with loss of one fluorine atom was observed when pentafluorophenyl substituted benzo[ghi]perylene triimide and perylene diimide were heated in N,N‐dimethylformamide, in which N,N‐dimethylformamide acted both as solvent and nucleophile reagent. Unexpectedly, the obtained product exhibited significant intramolecular charge transfer optical properties in solutions. The mechanism of nucleophilic substitution and the influence of substituent were further studied and proposed in this manuscript.

A reversible vapor-responsive fluorochromic molecular platform based on coupled AIE–ESIPT mechanisms and its applications in anti-counterfeiting measures

In this work, a series of 2-(2-hydroxyphenyl)benzothiazole (HBT) derivatives with an aggregation-induced emission–excited state intramolecular proton transfer (AIE-ESIPT) dual mechanism was synthesized. We systematically investigated their optical properties in solution, aqueous suspension, and the solid state. The fluorescence properties of these five compounds were highly dependent on the solvent environment. Particularly, DMSO and DMF were found to significantly promote deprotonation of the phenolic hydroxyl and favor fluorescence emission from the phenolic anion. The Keto or Enol forms generally could be transformed to phenolic anions with the aid of base in solution. The results from aggregation-induced emission enhancement (AIEE) and red-shifted AIE clearly illustrated the evolution process of the fluorescence spectra, indicating that the three luminescent species in the solution were transformable. The systematic investigation demonstrated that the desired fluorescence could be generated for HBT derivatives by varying the solvents or adding additives, such as base or water, to the solution. Because of the synergistic effect of AIE and ESIPT, these fluorophores exhibited high solid-state quantum yields and large Stokes shifts. These dyes also featured high photostability and tunable emission spectra covering most of the visible light region. Single crystal studies and theoretical calculations elucidated the luminescent properties. When loaded on filter paper, the HBT-based dyes exhibited high-efficiency fluorescence visualization and reversible solid-state luminescence switching under alternating amine and acid vapor treatments. These dyes were used on banknotes for anti-counterfeiting measures, demonstrating the practical applications of these molecules as security inks.