Theoretical study of static (Hyper)polarizabilities of twisted intramolecular charge transfer chromophores

Density functional theory calculations are performed to study the (hyper)polarizabilities of a series of planar and twisted intramolecular charge transfer molecules (tictoids) with different electron‐donating and electron‐withdrawing groups. Both similarity and difference between the planar and twisted molecules are noted in their (hyper)polarizability variation with respect to substituent and solvent dielectric constant. When compared with dramatic enhancements resulting from geometry twist and solvent effect, substitution to D/A pairs leads to relatively moderate variation in (hyper) polarizability. In addition, tictoids with different substituents may exhibit different solvent effects in their hyperpolarizability magnitudes. Our calculations suggest that the nonlinear optical response of the tictoids could be tuned by appropriately selecting the donor/acceptor pairs and solvents. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Synthesis of E,E-4-(6-(N-hydroxyethyl(N-ethyl)-aminostyrylquinoxalin-2-yl)vinyl)-2-dicyanomethylene-3-cyano-2,5-dihydrofurans

Abstract

Nonlinear-optical chromophores with N-hydroxyethyl-N-ethylaniline donor, tricyanofuran acceptor moieties and 3,7-divinylquinoxaline π-bridge have been synthesized. The acetyl derivatives of these chromophores exhibit an intense charge transfer band in the visible region of spectrum and a large positive and negative solvatochromism in different solvents.     

β-Cyclodextrin as a mimetic of the natural GFP-chromophore environment

The green fluorescent protein (GFP) chromophore has been anchored to β-cyclodextrin (βCD) via a copper(I)-catalyzed azide-alkyne cycloaddition. The photophysical properties of this new GFP-CD derivative have been evaluated, showing the formation of a self-inclusion complex and enhancement of fluorescence of the GFP-chromophore covalently bound to the βCD. This enhancement of fluorescence by encapsulation and hence fixation of the chromophore in a binding pocket mimics the effect exerted by the natural protein environment.     

Octupolar Derivatives Functionalized with Superacceptor Peripheral Groups: Synthesis and Evaluation of the Electron‐Withdrawing Ability of Potent Unusual Groups

Novel tripodal derivatives with a triphenylamine core and that bear “superacidifiers” (i.e., fluorinated sulfoximinyl blocks) or novel sulfiliminyl moieties as peripheral groups were synthesized. These new chromophores show strong absorption in the near‐UV region and emission in the visible region. The fluorinated sulfoximinyl moieties were found to behave as potent auxochromic and electron‐withdrawing (EW) groups, thus leading to redshifted absorption and emission. These moieties promote a core‐to‐periphery intramolecular charge transfer (ctp‐ICT) transition, the energy of which was found to be correlated to their EW strength. In this study, we provide evidence of a linear correlation between the Hammett constant (σ_p) values and the electronic gap between the ground and first excited state of the three‐branched derivatives. This in turn was used to derive σ_p values of fluorinated sulfoximinyl moieties. These EWGs show unprecedentedly high σ_p values, up to 1.45 relative to 0.8 for NO₂. Also, by using this method, the sulfiliminyl moiety was shown to exhibit similar EW strength as NO₂, while promoting improved transparency and solubility. Finally, the superior EW strength of the fluorinated sulfoximine peripheral moieties was shown to induce significant enhancement of the two‐photon absorption responses in the red near‐IR region of the three‐branched derivatives relative to similar octupoles that bear more usual strong EW groups. These characteristics (improved nonlinear responses or transparency) open new routes for the design of nonlinear optical (NLO) chromophores for optical limiting or electro‐optical modulation. Such building blocks could also be of interest for optoelectronic applications, including the development of solar cells.     

Efficient NIR‐Light Emission from Solid‐State Complexes of Boron Difluoride with 2′‐Hydroxychalcone Derivatives

This article describes a series of nine complexes of boron difluoride with 2′‐hydroxychacone derivatives. These dyes were synthesized very simply and exhibited intense NIR emission in the solid state. Complexation with boron was shown to impart very strong donor–acceptor character into the excited state of these dyes, which further shifted their emission towards the NIR region (up to 855 nm for dye 5 b , which contained the strongly donating triphenylamine group). Strikingly, these optical features were obtained for crystalline solids, which are characterized by high molecular order and tight packing, two features that are conventionally believed to be detrimental to luminescence in organic crystals. Remarkably, the emission of light from the π‐stacked molecules did not occur at the expense of the emission quantum yield. Indeed, in the case of pyrene‐containing dye 4 , for example, a fluorescence quantum yield of about 15 % with a fluorescence emission maximum at 755 nm were obtained in the solid state. Moreover, dye 3 a and acetonaphthone‐based compounds 1 b , 2 b , and 3 b showed no evidence of degradation as solutions in CH₂Cl₂ that contained EtOH. In particular, solutions of brightly fluorescent compound 3 a (brightness: ε×Φ_f=45 000 M ^?1 cm^?1) could be stored for long periods without any detectable changes in its optical properties. All together, these new dyes possess a set of very interesting properties that make them promising solid‐state NIR fluorophores for applications in materials science.     

不同基体刚性偶氮化合物光致光学各向异性及其唯象模拟

在不同刚性的聚合物基体聚甲基丙烯酸甲酯（PMMA）、聚乙烯咔唑（PVK）和聚苯乙烯（PS）薄膜基体中掺入相同质量分数（均为0．003）的分散红13（DRl3）偶氮染料。以线偏振连续Ar^＋激光（514nm）作为控制光,连续He-Ne激光（632．8nm）作为信号光考察了具有相同厚度的三种样品在相同控制光功率（15mW）下的光致双折射效应。实验发现刚性较大的聚乙烯咔唑基体样品的双折射效应最小,刚性最小的聚苯乙烯基体样品的双折射效应最大。在偶氮生色团光致异构的四能级模型基础上,建立一新的唯象的模型。在模型中引入描述聚合物基体刚性的参量s,通过数值计算描述了不同基体刚性参量s对偶氮生色团光致异构取向的影响。计算结果表明,基体的刚性越大,样品的光致双折射效应越小,定性地解释了实验现象。     

Electronic and vibronic contributions to two-photon absorption in donor-acceptor-donor squaraine chromophores

Many squaraines have been observed to exhibit two-photon absorption at transition energies close to those of the lowest energy one-photon electronic transitions. Here, the electronic and vibronic contributions to these low-energy two-photon absorptions are elucidated by performing correlated quantum-chemical calculations on model chromophores that differ in their terminal donor groups (diarylaminothienyl, indolenylidenemethyl, dimethylaminopolyenyl, or 4-(dimethylamino)phenylpolyenyl). For squaraines with diarylaminothienyl and dimethylaminopolyenyl donors and for the longer examples of 4-(dimethylamino)phenylpolyenyl donors, the calculated energies of the lowest two-photon active states approach those of the lowest energy one-photon active (1B(u)) states. This is consistent with the existence of purely electronic channels for low-energy two-photon absorption (TPA) in these types of chromophores. On the other hand, for all squaraines containing indolinylidenemethyl donors, the calculations indicate that there are no low-lying electronic states of appropriate symmetry for TPA. Actually, we find that the lowest energy TPA transitions can be explained through coupling of the one-photon absorption (OPA) active 1B(u) state with b(u) vibrational modes. Through implementation of Herzberg-Teller theory, we are able to identify the vibrational modes responsible for the low-energy TPA peak and to reproduce, at least qualitatively, the experimental TPA spectra of several squaraines of this type.