Helicenes: synthesis and applications.

This review draws a rather comprehensive picture of how Suzuki polycondensation was discovered in 1989 and how it was subsequently developed into the most powerful polymerization method for polyarylenes during the last 20 years. It combines insights into synthetic issues with classes of polymers prepared and touches upon aspects of this method's technological importance. Because a significant part of the developmental work was carried out in industry, the present review makes reference to an unusually large number of patents.

Suzuki Polycondensation: Polyarylenes à la Carte

Time-dependent Hartree–Fock and Moller–Plesset second-order calculations have been used to unravel the relationships between structure and first hyperpolarizability in spiropyran/merocyanine couples and therefore to design efficient second-order nonlinear optical switching compounds. Large first hyperpolarizabilities for the merocyanine form as well as large contrasts of first hyperpolarizability have been obtained when, on the same species, (i) substituents at R1 and R2 positions on the phenolate ring of the merocyanine form are strong acceptor and donor substituents, respectively, (ii) the ethylenic bridge is substituted by donor groups, (iii) the other aromatic part of the system is benzimidazolo rather than indolino or benzothiazolo, and (iv) strong donor substituents are placed on the benzimidazolo moiety.

In silico optimization of merocyanine-spiropyran compounds as second-order nonlinear optical molecular switches.

Molecular switches: Highly efficient acido- and photoswitchable frequency doublers (see scheme) based on the indolinooxazolidine core are studied by means of hyper-Rayleigh experiments and quantum-chemical calculations.

To optimize the nonlinear optical (NLO) contrast, a series of indolinooxazolidine derivatives with electron-withdrawing substituents in the para position on the indolinic residue have been synthesized. Their linear and nonlinear optical properties have been characterized by UV-visible absorption and hyper-Rayleigh scattering measurements, as well as by ab initio calculations. The two-way photo- or pH-triggered switching mechanism has been demonstrated by comparing the absorption spectra of the zwitterionic and protonated open forms (POF). Hyper-Rayleigh measurements have revealed that the second-order NLO contrast between the closed indolinooxazolidine and the open π-conjugated colored forms remain very large upon substitution. Theory and measurements show that for the POFs the amplitude of the first hyperpolarizability follows the Hammett parameters of the withdrawing groups. However, because the measurements are performed in resonance, to recover this behavior, elaborate procedures including homogeneous and inhomogeneous broadenings, as well as single-mode vibronic structures are necessary to extrapolate to the static limit.

Two‐Way Molecular Switches with Large Nonlinear Optical Contrast

In this paper, we report the first systematic experimental and theoretical investigation of the electric field induced second harmonic response of some tetrathia[7]helicene-based NLOphores. We studied six model compounds carrying the NO2, CH=CHCN, and COCF3 units as accepting groups on both the terminal thiophene positions as well as on the central benzene ring of the helicene backbone. These groups, known to be of medium and medium-strong accepting strength, allow tuning of both the electronic and structural properties of the helicenes studied. This experimental/theoretical study should set a milestone in addressing new structure-properties relationship of this class of nonconventional chiral chromophores able to show second order as well as third order NLO phenomena.

Theoretical and Experimental Investigation of Electric Field Induced Second Harmonic Generation in Tetrathia[7]helicenes†

The Pd-catalyzed cross-coupling reaction involving organostannanes (Stille reaction) is applied to prepare a series of N-t-BOC-protected D−π−A oligopyrroles. After purification, oligomers with one to four pyrrole units inserted between a 4-nitrophenyl and a 4-methoxyphenyl group are isolated in yields between 20 and 47%. Only minor differences in the linear optical properties are observed for the four oligomers. The charge-transfer band around λmax = 365 nm shows a small, unexpected, hypsochromic shift, while the π−π* band around λmax = 285 nm shows a small, expected, bathochromic shift upon elongation of the molecule. Their nonlinear optical properties, however, show a surprising proceeding; going from the D−π−A oligomer with one pyrrole unit to that with three pyrrole units, the hyperpolarizability, as measured by hyper-Rayleigh scattering, increases additionally with the number of pyrrole units within the oligomer, up to 277 × 10-30 esu in case of the trimer. On the basis of the assumption that both tr...

Synthesis and (Non)linear Optical Properties of a Series of Donor-Oligopyrrole-Acceptor Molecules,

Oxidation effects on the hyper-Rayleigh scattering (HRS) second-order nonlinear optical responses of homo- and hetero-helicenes have been investigated using the time-dependent Hartree-Fock approach and the Austin Model I semi-empirical Hamiltonian. Upon oxidation, this approach predicts a substantial increase of the HRS response, which, with the exception of tetrathia-[7]-helicene and pentathia-[9]-helicene, is accompanied by a decrease of the depolarization ratio. In the case of helicenes bearing thiophene units, the HRS increase is associated with the presence of a substantial axial contribution to the first hyperpolarizability, whereas the radial component is otherwise dominant. (c) 2005 Elsevier B.V. All rights reserved.

Hyper-Rayleigh scattering of neutral and charged helicenes (vol 412, pg 275, 2005)

Iron oxide/gold core-shell nanoparticulate systems are prepared in which a biologically active substance is either bound to the surface of the gold shell of the nanoparticle or is contained within the gold shell of the nanoparticle. Such systems are used for the targeted delivery of biologically active substances, hyperthermia treatment, imaging or combinations thereof. The core diameter of the said nanoparticles is between 5-150nm and thickness of the gold shell is typically between 1-50nm. Depending on the size of the core, the particles are single domain magnetic or superparamagnetic. The biologically active substances used may be attached to the shell through chemical bonding, for example by using thiol or amine groups. Optical properties of the nanoparticles (i.e., the wavelength at which the nanoparticles may absorb) can be controlled by varying shell thickness and core size.

Targeted delivery of biologically active substances using iron oxide/gold core-shell nanoparticles

Variable optical filter, at least consisting of an optical filter structure (2) with different zones (3A-3B-3C-3D-3E) and/or reflection surfaces (4A-4B-4C-4D-4E-4F) which are made such that light (L1) with a well-defined wavelength passes, whereas light (L2) with another wavelength is reflected, in particular according to the so-called Bragg principle, whereby this filter (1-1A-1B-1C) also is provided with means (7) for altering the optical characteristics of the filter structure (2), characterized in that the aforementioned means (7) at least consist in that, on one hand, the optical path of the aforementioned filter structure (2) comprises a portion (6) based on one or more polymers, which is configured as an optical cavity enclosed by refractive surfaces of the aforementioned filter structure, and the optical characteristics of which can be changed under the influence of an electric potential, an electric field (E), respectively, or under the influence of light and, on the other hand, the filter (1) is provided with means (7) with which, in a controlled manner, an electric potential can be generated over, respectively, an electric field (E) in the aforementioned portion (6), and/or an optical field in this portion.

Variable optical filter and devices applying such filter

In an exemplary method, a nano-architectured carbon structure is fabricated by forming a unit (e.g., a film) of a liquid carbon-containing starting material. A surface of the unit is nano-molded using a durable mold ( 122 ) that is pre-formed with a pattern of nano-concavities corresponding to a desired pattern of nano-features to be formed by the mold on the surface of the unit. After nano-molding the surface of the unit, the first unit is stabilized to render the unit and its formed nano-structures capable of surviving downstream steps. The mold is removed from the first surface to form a nano-molded surface of a carbonization precursor ( 152 ). The precursor is carbonized in an inert-gas atmosphere at a suitable high temperature to form a corresponding nano-architectured carbon structure ( 62 ). A principal use of the nano-architectured carbon structure is a carbon electrode used in, e.g., Li-ion batteries, supercapacitors, and battery-supercapacitor hybrid devices.

Nano-architectured carbon structures and methods for fabricating same

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