Optical Chromophores Research Articles

Two‐Photon Absorption Switches Based on Protonation of Pyrimidine Derivatives

AbstractThe photophysical and two‐photon absorption (TPA) properties of five push‐pull pyrimidine derivatives were studied upon protonation with trifluoroacetic acid (TFA). The pyrimidine heterocycles have been used as the protonation sites and electron acceptors while methoxy groups were employed as electron donors. Steady state and fluorescence time‐resolved spectroscopy from femtoseconds to nanoseconds have been used together with the two‐photon excited fluorescence method. Protonation with TFA resulted in red‐shifted absorption and fluorescence spectra as well as to an acceleration of the excited state dynamics. The TPA properties showed a remarkable enhancement upon protonation with a ten‐times increase of the TPA cross sections due to an increased intramolecular charge transfer. Our results demonstrate the potential of pyrimidine chromophores to be used as protonation tunable non‐linear optical chromophores.

Synthesis of Bis(N,N-diethyl)aniline-Based, Nonlinear, Optical Chromophores with Increased Electro-Optic Activity by Optimizing the Thiolated Isophorone Bridge

Six nonlinear, optical chromophores, Z1–Z6, based on the bis(N,N-diethyl)aniline-derived donor and thiolated isophorone bridge, were designed and synthesized. The bis(N,N-diethyl)aniline-derived donor was applied in a chromophore with thiolated isophorone as an electron bridge for the first time. In particular, the bridge parts of chromophores Z2–Z6 were modified with different functional groups, including tert-butyltrimethylsilane and tert-butyl(methyl)diphenylsilane derivative: 1,3-bis(trifluoromethyl)benzene and alkylaniline cyanoacetate, respectively. Density functional theory calculations suggested this series of chromophores show much greater hyperpolarizability than traditional, nonlinear, optical chromophores due to strong electron donor ability. These chromophores, Z1–Z6, showed very high poling efficiencies due to the large steric hindrance and hyperpolarizability of the chromophores. A large poling efficiency (2.04 ± 0.08 nm2/V2) and r33 value (193 pm/V) were achieved for polymeric thin films doped with 25 wt% chromophore Z6 at 1310 nm.

Self-Reporting Polysaccharide Polymersome for Doxorubicin and Cisplatin Delivery to Live Cancer Cells.

We report self-reporting fluorescent polysaccharide polymersome nanoassemblies for enzyme-responsive intracellular delivery of two clinical anticancer drugs doxorubicin (DOX) and cisplatin to study the real-time drug-releasing aspects by fluorescent resonance energy transfer (FRET) bioimaging in live cancer cells. Fluorescent polymersomes were tailor-made by tagging an aggregation-induced emission (AIE) optical chromophore, tetraphenylethylene (TPE), and a plant-based vesicular directing hydrophobic unit through enzyme-biodegradable aliphatic ester chemical linkages in the polysaccharide dextran. The blue-luminescent polymersome self-assembled in water and exhibited excellent encapsulation capability for the red-luminescent anticancer drug DOX. FRET between the AIE polymersome host and DOX guest molecules resulted in a completely turn-off probe. At the intracellular level, the lysosomal enzymatic disassembly of the polymersome restored the dual fluorescent signals from DOX and TPE at the nucleus and the lysosomes, respectively. Live-cell confocal microscopy coupled with selective photoexcitation was employed to study the real-time polymersome disassembly by monitoring the turn-on fluorescent signals in human breast cancer cell lines. Alternatively, carboxylic acid-functionalized AIE polymersomes were also tailor-made for cisplatin stitching to directly monitor Pt drug delivery. The polymersome nanoassemblies exhibited excellent structural tolerance for the chemical conjugation of the Pt drugs, and the fluorescence signals were unaltered. An in vitro drug release study confirmed that the cisplatin-stitched fluorescent polymersomes were very stable under physiological conditions and underwent lysosomal enzymatic degradation to inhibit the cancer cell growth. A lysosomal colocalization experiment using confocal microscopy substantiates the enzyme-responsive degradation of these polymersomes to release both the encapsulated and conjugated drugs at the intracellular level. The present design provides a unique opportunity to deliver more than one anticancer drug from a single polymersome platform in cancer research.

Calculation of the Structure and Properties of Optical Nonlinear Fluorine-Containing Chromophores

Possible modifications of chromophore structures with nonlinear optical properties by bonding F atoms and F-containing groups to the acceptor site of the molecules are considered. Quantum chemical calculations of dipole moments and first hyperpolarizability were performed for several nonlinear chromophores based on N-ethyl- N-(2-hydroxyethyl)-4-phenylazoaniline and modified by the addition of F atoms and F-containing groups to the acceptor site. Positions of maxima in the electronic absorption spectrum and the Mulliken charges on the atoms are found. It is shown that addition of F atoms and F-containing groups to the chromophore acceptor site changes (increases) the efficiency parameter, defined as the product of the dipole moment and the first hyperpolarizability. The main parameters of a waveguide modulator made of an electro-optical polymer composite with F-containing chromophores embedded in it are estimated.

Quantum-Classical Electron as an Organizing Principle in Nature

We are introducing briefly to the new theory of “quantum” transitions in molecular and chemical physics — quantum-classical mechanics, in which an electron behaves dynamically in two ways: both as a quantum and as a classical elementary particle. Namely, in the initial and final adiabatic states of molecular “quantum” transitions, the light electron exhibits its quantum properties. On the contrary, in the transient molecular state, the electron, provoking the so-called dozy chaos in the vibrational motion of very heavy nuclei “in order” to shift the equilibrium positions of their vibrations to new positions corresponding to the new distribution of the electron charge, because of the continuous energy spectrum in the transient state, manifests itself as a classical elementary particle. The article discusses mainly studied and some promising applications of the organizing role of an electron in nature. Among the well-studied applications, the quantum-classical organization of optical absorption band shapes in polymethine dyes and their J-aggregates is discussed. For example, the well-known narrow and intense J-band of J-aggregates is one of the striking examples of the implementation of the so-called Egorov resonance, in which the motion of the reorganization of the nuclei of the environmental medium significantly contributes to the electron transition in the optical pi-electron chromophore of J-aggregates. This effect can also be interpreted as the transfer of dozy chaos from the peak of the J-band into its wing by a chaotic motion of the quantum-classical pi-electron state of the J-chromophore. The dynamic role of the quantum-classical electron in the joint organization of the absorption and luminescence spectra, and an extension of quantum-classical mechanics to nonlinear optical processes are discussed. The probable leading role of quantum-classical electrons in the evolution of molecular matter and possibility of applications of quantum-classical mechanics to the study of cancer and viruses are discussed as a future research perspective.

Laser-stimulated Pockels effect in CdBr2/Cu polymer nanocomposites

Abstract Photostimulated linear electrooptical effects (LEOEs) in the CdBr2/Cu polymer nanocomposites have been established. The phototreatment was carried out using two bicolor coherent beams with Er: glass laser pulses at coherent frequencies 1540 nm and 770 nm. The detection of the LEOE was performed by three wavelengths (633 nm, 1150 nm, and 3390 nm) of continuous-wave (cw) He–Ne laser. The monitoring of the laser-stimulated LEOE has been done immediately after illumination, using the Senarmont method. The fundamental beam was formed by Er: glass laser with pulse time duration about 20 ns and pulse frequency repetition about 10 Hz. The nanocrystallites of the layered crystallites possessed a thickness varying from 1 nm to 200 nm. The contents of the composites have been varied in the polyvinyl alcohol (PVA) matrices. The principal role here is played by Cu ions participating in the ionic conductivity, which favors an internal charged dc-electric field and related photorefraction. The later, in turn, is sensitive to the wavelengths of probing beams. We explored both dependences versus the nanocrystalline thickness as well as the nonlinear optical (NLO) chromophore concentration. This particular study is devoted to the microscopy of the laser-stimulated changes of the crystallites embedded into the matrices.

Synthesis and electro-optic properties of novel Y-type polyimide containing nitrothiazolylazodioxyphenyl group

New Y-type polyimide (5) containing nitrothiazolylazodioxyphenyl groups as nonlinear optical (NLO) chromophores, which are components of the polymer backbone, was prepared and characterized. Polyimide 5 is soluble in common organic solvents such as N,N-dimethylformamide and dimethylsulfoxide. Polyimide 5 shows a thermal stability up to 300 °C in thermogravimetric analysis with glass-transition temperature (Tg) obtained from differential scanning calorimetry near 130 °C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at the 1064 nm fundamental wavelength is around 2.32 pm/V. The dipole alignment of polymer 5 exhibits a thermal stability even at 5 °C higher than Tg, and there is no SHG decay below 135 °C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

A π‐Conjugated Chromophore Dye and Its Functional Paper Strips for Visually On‐Site Sensing F− and Its Reaction Mechanism

AbstractAn improved D−A‐D typed π‐conjugated optical chromophore (PBHPI) with multi‐activated recognition sites and its functionalized testing‐paper strips were constructed and developed, for the first time, based on B3LYP/6‐31G level of theory in Gaussian 03 suite. After its UV‐vis spectral property was investigated in detail, it was noted to find that the target PBHPI and its functionalized paper strips could conclusively react with F− with obvious color change from light yellow to dark red. Under the optimized experimental conditions, both PBHPI and its functionalized paper‐strips could selectively recognize F− with a double‐wavelength colorimetric response to realize a wide linear range from 5.0 ×10–6 mol/L to 1.4 ×10–4 mol/L. The present sensing systems were successfully applied for visually on‐site monitoring F− in some commercial organic and toothpaste samples simply and conveniently. The recognition mechanism was confirmed to be the deprotonating mechanism to form multiple hydrogen bonds as what we expected.

Synthesis of Novel Chromophore Based on Tricyanocyclopentenone Acceptor and Its NLO Property

Novel organic second Nonlinear optical (NLO) chromophore GZP-T based on tricyanocyclopentenone electronic acceptor group were designed and synthesized in this paper. The structure of chromophore GZP-T is characterized by mass spectrum and nuclear magnetic resonance spectroscopy. And chromophore FTC based on traditional tricyanofuran electronic acceptor was also prepared as the contrast. Their delocalized energy levels were estimated by UV–VIS spectra. Their thermal properties were studied by thermogravimetric analysis (TGA). Obviously, chromophore GZP-T showed lower delocalized energy levels and higher thermal decomposition temperature (just about 290 °C). The poled films showed the largest second-order nonlinear optical coefficients of 103.1 and 68.6 pm/V, respectively, for chromophore GZP-T and FTC. These advantages of chromophore GZP-T are attributed to the improvement of first-order hyperpolarizability and the attenuatation of intermolecular dipole interaction by the introduction of tricyanocyclopentenone electronic acceptor. And in another word, tricyanocyclopentenone electronic acceptor may be a promising way to drastically change the nonlinear optical features of the titled compounds and show a direction of designing new electron acceptor in the field of nonlinear optical materials.

Repeated and Folded DNA Sequences and Their Modular Ag106+ Cluster

Molecular silver clusters are optical chromophores, and species with distinct spectra form with DNA strands. One such hybrid chromophore is a violet cluster bound to repeated C2X sequences where X ≠ C. We varied the number of C2X repeats and the X nucleobase and consider three observations. First, different lengths of (C2A)y and (C2T)y strands with y = 3–12 identify a minimal (C2X)6 scaffold that forms a specific Ag10 adduct. This cluster has a +6 oxidation state, absorbs between 400–450 nm, and folds its DNA host. Second, different X nucleobases alter the (C2X)6 binding site. The natural nucleobases preferentially form the Ag106+ cluster and yield strong circular dichroism. These ligands coordinate via their heteroatoms, and the N3 of thymine was identified via cluster fluorescence that varies with pH. In contrast, abasic sites and imidazole substitutions suppress circular dichroism and diminish the number of silver adducts. These observations suggest that a (C2X)6 coordinates Ag106+ via multiple nucleobases. Third, beyond the minimal (C2X)6 binding site, longer strands still form Ag106+ but can also coordinate additional Ag+ adducts. The added Ag+ do not perturb the Ag0 and their spectra and thus may partition to open C2X subunits outside the core (C2X)6–Ag106+ complex. Thus, these modular complexes distinguish oxidized and reduced silvers. Collectively, these three observations suggest that the DNA and silver cluster play complementary roles: a repeated C2X sequence stabilizes the Ag106+ cluster, while the cluster folds its host. We specifically suggest that the Ag+ within Ag106+ cross-links remote C2X subunits and the Ag0 coordinate with mismatch sites in a hairpin-like secondary structure. Distinct roles for Ag+ and Ag0 within a cluster are considered in light of the X-ray spectra of related complexes.

Synthesis and properties of novel nonlinear optical polyester containing carbomethoxycyanovinylnitrocatecholic group

ABSTRACTA new X-type polyester 5 containing 4-(2′-carbomethoxy-2′-cyano)vinyl-5-nitrocatecholic groups as nonlinear optical (NLO) chromophores, which are parts of the polymer backbone, was prepared and studied its properties. Polyester 5 is soluble in common organic solvents such as acetone and dimethylsulfoxide. Polymer 5 shows a thermal stability up to 280°C from thermogravimetric analysis with glass-transition temperature (Tg) obtained from differential scanning calorimetry of near 110°C. The second harmonic generation (SHG) coefficient (d33) of poled polymer 5 film at the 1064 nm fundamental wavelength is 6.13 × 10−9 esu. The dipole alignment of polymer 5 exhibits a thermal stability up to Tg, and no significant SHG decay is observed below 110°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

Synthesis and nonlinear optical properties of novel polyester containing dicyanovinylnitrocatecholic group

ABSTRACTA novel X-type polyester containing 4-(2′,2′-dicyanovinyl)-5-nitrocatecholic groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. The polyester is soluble in common organic solvents such as N,N-dimethylformamide and acetone. It shows a thermal stability up to 300°C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 105°C. The second harmonic generation (SHG) coefficient (d33) of a poled polymer film at the 1064 nm fundamental wavelength is 5.31 × 10−9 esu. The dipole alignment exhibits a thermal stability even at 5°C higher than glass-transition temperature (Tg), and no significant SHG decay is observed below 110°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

A DNA-Encapsulated and Fluorescent Ag106+ Cluster with a Distinct Metal-Like Core

Silver cluster–DNA complexes are optical chromophores, and pairs of these conjugates can be toggled from fluorescently dim to bright states using DNA hybridization. This paper highlights spectral and structural differences for a specific cluster pair. We have previously characterized a cluster with low emission and violet absorption that forms a compact structure with single-stranded oligonucleotides. We now consider its counterpart with blue absorption and strong green emission. This cluster develops with a single-stranded/duplex DNA construct and is favored by low silver concentrations with ≲8 Ag+:DNA, an oxygen atmosphere, and neutral pH. The resulting cluster displays key signatures of a molecular metal with well-defined absorption/emission bands at 490/550 nm, and with a fluorescence quantum yield of 15% and lifetime of 2.4 ns. The molecular cluster conjugates with the larger DNA host because it chromatographically elutes with the DNA and it exhibits circular dichroism. The silver cluster is identified as Ag106+ using two modes of mass spectrometry and elemental analysis. Our key finding is that it adopts a low-dimensional shape, as determined from a Ag K-edge extended X-ray absorption fine structure analysis. The Ag0 in this oxidized cluster segregates from the Ag+ via a sparse number of metal-like bonds and a denser network of silver–DNA bonds. This structure contrasts with the compact, octahedral-like shape of the violet counterpart to the blue cluster, which is also a Ag106+ species. We consider that the blue- and violet-absorbing clusters may be isomers with shapes that are controlled by the secondary structures of their DNA templates.

Formation of channel optical waveguides in polymethylmethacrylate with embedded electro-optic chromophore DR13 by the photoinduced bleaching method

A composite polymeric material based on polymethylmethacrylate (PMMA) with embedded electro- optical (EO) chromophore DR13 is designed. Irradiation with electromagnetic radiation in the visible range leads to a bleaching of the composite and its refractive index n decreases due to the irreversible photodestruction of the chromophore. Changes in the absorption spectrum and refractive index of the composite with the irradiation time are measured. It is shown that the change in n depends on the concentration of DR13 in the polymer matrix and can reach a value of Δn = 0.034 in the telecommunication C-range near a wavelength of 1.55 μm. The rate of bleaching depends on the wavelength of the actinic light and reaches its maximum when the wavelength is near the maximum of chromophore absorption. With the use of the photobleaching method and the PMMA/DR13 composite, channel waveguides and the other elements of the integrated optical devices are fabricated, including waveguide splitters, directional couplers, and Mach–Zehnder interferometers. This simple one-step method does not involve the removal of polymer material by liquidphase or reactive ion etching.

Alternative bridging architectures in organic nonlinear optical materials: comparison of π- and χ-type structures

Organic nonlinear optical (ONLO) chromophores are used to make electro-optic devices. Traditional ONLO chromophores use a π-conjugated bridge to couple the electron acceptor and donor moieties. We have explored whether other types of conjugation can be used to make high-performance ONLO chromophores. We have found that cross-conjugated bridge structures, when other parameters are kept the same, can exhibit comparable hyperpolarizabilities. Experimental hyperpolarizabilities of prototypical cross-conjugated chromophores, measured by hyper-Raleigh scattering, are comparable with their π-conjugated analogues, in contrast with the prediction of several electronic structure calculation methods. This opens new synthetic routes to other types of chromophores, which may provide enhanced performance.

Collimated light reflection and transmission of a surface partially covered by large and tenuous particles.

We derive simple approximate expressions for the reflectivity and transmissivity of light from disordered monolayers of tenuous particles of dimensions larger than the wavelength and supported by a flat interface. The expressions derived can be used for different particle shapes and for moderate angles of incidence. We then investigate the effects of particle shape and orientation on reflectivity and transmissivity spectra of a monolayer of tenuous particles containing an optical chromophore in a solution in their interior. We also simulate the effects of a particle's shape and orientation on the angle dependence of the optical reflectivity and transmissivity. In our examples, we consider disordered monolayers of particles analogous to some biological cells.

Synthesis and nonlinear optical properties of novel polyester containing nitrothiazolylazoresorcinoxy group

ABSTRACTNovel Y-type polyester 4 containing 4-(5-nitro-2-thiazolylazo)re-sorcinoxy group as nonlinear optical (NLO) chromophore, which constitutes parts of the polymer backbone, was prepared and characterized. Polyester 4 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. Polyester 4 shows a thermal stability up to 240°C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 106°C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at the 1064 nm fundamental wavelength is 8.43 × 10−9 esu. The poled polymer film exhibits an enhanced thermal stability of dipole alignment and there was no negligible decay of the SHG signal over hundreds of hours at 70°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

A Segregated, Partially Oxidized, and Compact Ag10 Cluster within an Encapsulating DNA Host.

Silver clusters develop within DNA strands and become optical chromophores with diverse electronic spectra and wide-ranging emission intensities. These studies consider a specific cluster that absorbs at 400 nm, has low emission, and exclusively develops with single-stranded oligonucleotides. It is also a chameleon-like chromophore that can be transformed into different highly emissive fluorophores. We describe four characteristics of this species and conclude that it is highly oxidized yet also metallic. One, the cluster size was determined via electrospray ionization mass spectrometry. A common silver mass is measured with different oligonucleotides and thereby supports a Ag10 cluster. Two, the cluster charge was determined by mass spectrometry and Ag L3-edge X-ray absorption near-edge structure spectroscopy. Respectively, the conjugate mass and the integrated white-line intensity support a partially oxidized cluster with a +6 and +6.5 charge, respectively. Three, the cluster chirality was gauged by circular dichroism spectroscopy. This chirality changes with the length and sequence of its DNA hosts, and these studies identified a dispersed binding site with ∼20 nucleobases. Four, the structure of this complex was investigated via Ag K-edge extended X-ray absorption fine structure spectroscopy. A multishell fitting analysis identified three unique scattering environments with corresponding bond lengths, coordination numbers, and Debye-Waller factors for each. Collectively, these findings support the following conclusion: a Ag10(+6) cluster develops within a 20-nucleobase DNA binding site, and this complex segregates into a compact, metal-like silver core that weakly links to an encapsulating silver-DNA shell. We consider different models that account for silver-silver coordination within the core.

Synthesis and Properties of Novel Nonlinear Optical Polyester Containing Cyanovinylnitroresorcinoxy Group

Novel X-type polyester 5 containing 4-(2’-carbomethoxy-2’-cyano)vinyl-6-nitroresorcinoxy group as nonlinear optical (NLO) chromophore, which constitutes parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. Polyester 5 shows a thermal stability up to 280°C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 116°C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at the 1064 nm fundamental wavelength is 4.25 × 10−9 esu. The dipole alignment exhibits a thermal stability even at 4°C higher than glass-transition temperature (Tg), and no significant SHG decay is observed below 120°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.

Synthesis and electro-optic properties of novel X-type polyester containing dioxynitrobenzylidenecyanoacetate with highly enhanced thermal stability of dipole alignment

Novel X-type polyester 5 containing 5-nitro-2,4-dioxybenzylidenecyanoacetate groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. Polymer 5 shows a thermal stability up to 280 °C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 116 °C. The second harmonic generation (SHG) coefficient (d 33) of poled polymer film at the 1064 nm fundamental wavelength is 1.78 pm V−1. The dipole alignment exhibits a thermal stability even at 4 °C higher than glass-transition temperature (T g), and no significant SHG decay is observed below 120 °C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.