Optical Properties Of Chromophores Research Articles

Hierarchical Modeling of the Nonlinear Optical Response of Composite Materials Based on Tetrathiafulvalene Derivatives.

The presented work concerns computational investigations of the physical properties of composite materials based on polymer matrix and nonlinear optical (NLO) active chromophores. The structural, electronic, and optical properties of selected tetrathiafulvalene (TTF)-based chromophores have been calculated using quantum chemical methods. The polymer matrix changes the physical properties of the inserted chromophores influencing their optical parameters. To explain the mechanism of the NLO signal occurrence from the composites based on poly(methyl methacrylate) (PMMA) matrix and TTF chromophores, their structures are modeled using the classical molecular dynamics. In consequence, the structural properties of the composites are discussed according to the NLO requirements. By developing the theoretical model based on a discrete multipole local field approach, the impact of polymer matrix on the optical properties of chromophores is explained.

Internal Stark effect of single-molecule fluorescence

The optical properties of chromophores can be efficiently tuned by electrostatic fields generated in their close environment, a phenomenon that plays a central role for the optimization of complex functions within living organisms where it is known as internal Stark effect (ISE). Here, we realised an ISE experiment at the lowest possible scale, by monitoring the Stark shift generated by charges confined within a single chromophore on its emission energy. To this end, a scanning tunneling microscope (STM) functioning at cryogenic temperatures is used to sequentially remove the two central protons of a free-base phthalocyanine chromophore deposited on a NaCl-covered Ag(111) surface. STM-induced fluorescence measurements reveal spectral shifts that are associated to the electrostatic field generated by the internal charges remaining in the chromophores upon deprotonation.

Exciton Delocalization and Scaffold Stability in Bridged Nucleotide-Substituted, DNA Duplex-Templated Cyanine Aggregates.

Molecular excitons play a foundational role in chromophore aggregates found in light-harvesting systems and offer potential applications in engineered excitonic systems. Controlled aggregation of chromophores to promote exciton delocalization has been achieved by covalently tethering chromophores to deoxyribonucleic acid (DNA) scaffolds. Although many studies have documented changes in the optical properties of chromophores upon aggregation using DNA scaffolds, more limited work has investigated how structural modifications of DNA via bridged nucleotides and chromophore covalent attachment impact scaffold stability as well as the configuration and optical behavior of attached aggregates. Here we investigated the impact of two types of bridged nucleotides, LNA and BNA, as a structural modification of duplex DNA-templated cyanine (Cy5) aggregates. The bridged nucleotides were incorporated in the domain of one to four Cy5 chromophores attached between adjacent bases of a DNA duplex. We found that bridged nucleotides increase the stability of DNA scaffolds carrying Cy5 aggregates in comparison with natural nucleotides in analogous constructs. Exciton coupling strength and delocalization in Cy5 aggregates were evaluated via steady-state absorption, circular dichroism, and theoretical modeling. Replacing natural nucleotides with bridged nucleotides resulted in a noticeable increase in the coupling strength (≥10 meV) between chromophores and increased H-like stacking behavior (i.e., more face-to-face stacking). Our results suggest that bridged nucleotides may be useful for increasing scaffold stability and coupling between DNA templated chromophores.

Electronic and optical properties of chromophores from bacterial cellulose

We report a systematic computational investigation on the electronic and optical properties of the principal chromophores found in bacterial cellulose (BC). In particular, we focus on the three chromophoric leading structures that were isolated from aged BC (1) 2,5-dihydroxy-[1,4]benzoquinone (2) 5,8-dihydroxy-[1,4]naphthoquinone and (3) 2,5-dihydroxyacetophenone. For the isolated molecules we performed all-electrons density functional theory (DFT) and time dependent DFT calculations with a localized Gaussian basis set and the hybrid exchange correlation functional B3LYP. We quantified key molecular properties relevant as electron affinities, ionization energies, quasi-particle energy gaps, optical absorption spectra, and exciton binding energies. We address moreover the impact of the solvent on the optical properties of the above systems using starting configurations obtained after classical molecular dynamics simulations in water. Our results could be of importance to comprehend the mechanisms underlying the processes of degradation of BC, which are of fundamental relevance for cultural heritage applications.

Synthesis of push-pull chromophores including an N-[4-(4-methoxyphenoxy)butyl]carbazole fragment

Organic substances with nonlinear optical properties of the second order are the promising materials for molecular electronics and photonics, that is, finally, for telecommunication and electro optical devices [1–6]. These materials possess some advantages if compared with their inorganic analogs: they have high values of nonresonance susceptibility, high nonlinear optic response, high transmissibility, low dielectric permittivity, besides they are sufficiently easy to process and economic [1, 7]. However certain drawbacks in their practical application also exist, e.g., the strong intermolecular electrostatic interaction, poor solubility in common organic solvents, thermal and photochemical instability. By altering the chemical structure of material, namely, by selecting the optimum electron-donor and electron-acceptor substituents it is possible to obtain the maximum nonlinearity on the molecular level and also affect the chemical, photochemical, and thermal stability. The introduction of electron-donor orthoor para-alkoxyphenyl groups into the monomers is known to change the optical properties of chromophores. It results in increasing of the electro optic coefficient value (r33) and molecular hyperpolarizability β [8–10]. When such a group is situated in the peripheral part of a long aliphatic chain and is incorporated into the chromophore structure both intermolecular and intramolecular interaction may occur between the donor and acceptor parts of the chromophore. Besides, the introduction of long-chain substituents in the structure of compounds affects the character of their packing in the solid state and their thermal stability [11]. In this work we continued to study carbazolecontaining compounds including in their structure ω(4-methoxyphenyl)alkyl substituents at the nitrogen atom of this heterocycle [12, 13] and have synthesized two new chromophores 8 and 9 including N-[4-(4methoxyphenoxy)butyl]carbazole moiety as a donor fragment. The optical and electrochemical properties of all prepared during thes work compounds were examined. First from the corresponding α,ωdibromoalkane and p-methoxyphenol 1 in acetone the starting bromides 2 and 3 were prepared [12]. The subsequent alkylation of carbazole with the synthesized bromides under the conditions of the phasetransfer catalysis in the system acetone–16 M water solution of NaОН–benzyltriethylammonium chloride led to the formation of the corresponding N-substituted carbazoles 4 and 5 [13]. The acetylation of the latter at room temperature in dichloroethane in the presence of SnCl4 afforded 3-acetylcarbazoles 6 and 7.

吡嗪-2-羧酸在γ-改性磷酸锆中的插层组装及发光性能

采用直接沉淀法制备了层状框架γ-磷酸锆(γ-ZrP)及改性磷酸锆(γ-DDZrP),通过插层化学法将吡嗪-2-羧酸生色团与改性磷酸锆进行杂化组装。X射线衍射结果显示,γ-DDZrP的层间距(3.70 nm)远远大于γ-ZrP(1.11 nm),这有利于吡嗪-2-羧酸生色团的插入。组装后层状框架的层间距由3.70 nm减小为3.33~3.29 nm。荧光光谱表明,最大发射峰位置发生了明显蓝移,由溶液中的373 nm蓝移至悬浮液的366 nm。研究发现,吡嗪-2-羧酸在水溶液中的荧光强度很低,但形成插层组装后,悬浮液的荧光强度有了很大程度的提高,当浓度为15μmol/L时,荧光强度增大了6倍。这说明γ-DDZrP能够改善吡嗪-2-羧酸的荧光性能,有利于其在分子识别和荧光探针等领域的应用。

Optical Properties of Chromophores with Different Six-Membered N-Heterocyclic Aromatic Ring

A series of intramolecular charge transfer (ICT) molecules containing six-membered N-heterocyclic electron acceptors, as well as their phenyl analogue, have been synthesized. The pyrazine derivatives exhibit the largest quantum yield, stokes shift and the longest emission maxima wavelength due to the appropriate electronegativity of pyrazine, while the triazine derivative has much lower quantum yield due to its too strong ICT. The methyl groups at N-heterocyclic rings also have influence on the optical properties by disturbing the molecular dipole moment.

Computational Nanoscience with NWChem

The NWChem software as been used to examine many nanoscale systems and their properties over the years. In this paper, an overiew of the general capabilities of NWChem is given as well as more specific details on the planewave and Gaussian based density functional codes usually used for nanoscale investigations. Examples are given of the scientific literature using NWChem, as well as two case studies: 1) Band gaps in oxides using exact-exchange based exchange-correlation functionals with the planewave DFT module, 2) Optical properties of chromophores using the Gaussian based DFT module.

Synthesis and Nonlinear Optical Properties of Chromophores with 1,8‐Dimethoxy‐9,10‐dihydroanthracene and Ring‐locked Triene

Abstract The new chromophore molecules with nonlinear optical (NLO) properties were prepared by Knoevenagel condensation from 1,8‐dimethoxy‐4,5‐diformyl‐9,10‐dihydroanthracene and isophorone derivative in the presence of piperidine and acetic acid. In these chromophore, the ring‐locked trienes were employed as the conjugation bridge and electron acceptor in D‐π‐A units. The key intermediate dialdehyde was conveniently prepared via a three step reaction, in which 1,8‐dimethoxyanthraquinone was reduced with zinc/acetic acid and sodium/ethanol successively, followed by formylation with 1,1‐dichlorodimethyl ether in the presence of TiCl4. The solvatochromism indicate that they have higher second‐order nonlinear hyperpolarizability μβ values than the corresponding reference compound, without red shift of the charge transfer band.

Reversible Change in Optical Properties of Chromophores in Zeolites by Interaction with Alkali Metal Cations

Reversible color changes of chromophores in cationic zeolites were investigated in order to elucidate the effect of cations and chromophores on the color change. We prepared a series of alkali metal cation exchanged zeolite Y and mordenite accommodating N,N-dimethyl-p-nitroaniline (DMpNA) molecules. The UV−vis absorption spectra showed an extraordinarily large red shift of the π−π* bands of DMpNA in the dehydrated form. The degree of the red shift is larger as the size of the cation decreases. 13C MAS NMR spectra showed sites and dynamic behavior of DMpNA. The color change behavior was also examined for p-nitroaniline and N-methyl-p-nitroaniline in NaY. Large red shifts of the π−π* bands were again observed in the dehydrated form, and the degree of the band shift was correlated well with the scale of susceptibility of the chromophores to the solvent polarity. These results indicated that the color change behavior depended on the combination of cationic zeolites and guest chromophores.