The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Frequency down-conversion of solid-state laser sources to the mid-infrared spectral range using non-oxide nonlinear crystals

A crucial goal for modern telecommunications systems is development of very high-speed components for broadband (>100 GHz), all-optical signal/information processing. The core component of such technologies is the electro-optic modulator, which encodes electrical signals onto fibre-optic transmissions. A significant challenge therefore is obtaining materials that have large electro-optic responses and that can be readily fabricated into devices at low cost. We report here on the realization of high-response heteroaromatic organic chromophores that can be straightforwardly self-organized from the vapour phase into intrinsically acentric, high-quality, micrometre-scale films. These π-conjugated electro-optically active films (with second-order susceptibilities up to ∼100 pm V−1) are thermally stable and conveniently grown by a simple physical vapour deposition process in a few hours. Supramolecular acentricity is achieved without electric field poling, enforced by biomimetic heterocycle–hydroxycarbonyl head-to-tail hydrogen-bonding.

Very large electro-optic responses in H-bonded heteroaromatic films grown by physical vapour deposition

We show that strong noncovalent interactions between a host polymer and guest dye molecules drastically suppress the dye aggregation tendency, thereby allowing high doping levels, which in turn opens possibilities for enhanced performance. We use a common azo-dye (Disperse Red 1) and three polymer matrixes:  polystyrene (PS), poly(4-vinylphenol) (PVPh), and poly(styrenesulfonic acid) (PSSA). The polymer−dye systems are studied in thin films by ultraviolet−visible and infrared spectroscopy and by optical second-harmonic generation. The lack of interaction in PS-matrix limits the maximum obtainable dye loading without aggregation below 20 wt %. Due to the polar nature of PVPh matrix, ca. 40 wt % dye loading can be achieved without aggregation, whereas in PSSA an ionic complex is formed, allowing ca. 60 wt % loading. In the latter case a dye molecule is attached to approximately each polymer unit, which has typically required covalent bonding of dye molecules to the polymer. This motivates further studies of...

Polymer−Dye Complexes: A Facile Method for High Doping Level and Aggregation Control of Dye Molecules

Harnessing supramolecular interactions in organic solid-state devices: Current status and future potential

Hydrogen‐Bond‐Directed Orientation in Nonlinear Optical Thin Films

We studied the effects of cryogenic cooling of a 2-[3-(4-hydroxystyryl)-5, 5-dimethylcyclohex-2-enylidene] malononitrile (OH1) crystal on the generation of broadband THz pulses via collinear optical rectification of 1350 nm femtosecond laser pulses. Cooling of the OH1 crystal from room temperature to 10 K leads to a ~10% increase of the pump-to-THz energy conversion efficiency and a shift of the THz pulse spectra to a higher frequency range. Both effects are due to the temperature variation of the THz absorption and the refractive index of the OH1 crystal. This conclusion has been verified by temperature dependent measurements of the linear absorption in the THz frequency region. An approach to obtain a stronger increase of the THz generation efficiency at cryogenic cooling of the OH1 crystal is discussed.

https://archive-ouverte.unige.ch/unige:36307/ATTACHMENT01

Generation of broadband THz pulses in organic crystal OH1 at room temperature and 10 K

We studied the effects of cryogenic cooling of a 2-[3-(4-hydroxystyryl)-5, 5-dimethylcyclohex-2-enylidene] malononitrile (OH1) crystal on the generation of broadband THz pulses via collinear optical rectification of 1350 nm femtosecond laser pulses. Cooling of the OH1 crystal from room temperature to 10 K leads to a ~10% increase of the pump-to-THz energy conversion efficiency and a shift of the THz pulse spectra to a higher frequency range. Both effects are due the temperature variation of THz absorption and the refractive index of the OH1 crystal. This conclusion has been verified by temperature dependent measurements of the linear absorption in the THz frequency region.

We present simulations for a design of a high-energy single-stage mid-IR difference frequency generation adapted to a two-color Ti:sapphire amplifier system. The optimized mixing process is based on chirped pulse difference frequency generation (CP-DFG), allowing for a higher conversion efficiency and reduced two-photon absorption losses. The numerical start-to-end simulations include stretching, chirped pulse difference frequency generation and pulse compression. Realistic design parameters for commercially available nonlinear crystals (GaSe, AgGaS2, LiInSe2, LiGaSe2) are considered. Compared with conventional unchirped DFG directly pumped by Ti:sapphire technology, we predict a threefold increase in the quantum efficiency. Our CP-DFG scheme provides up to 340 mu J pulse energy directly at 7.2 mu m when pumped with 8 mJ and supports a bandwidth of up to 350 nm. The resulting 240 fs mid-IR pulses are inherently phase stable.

/pdf/design-of-efficient-single-stage-chirped-pulse-difference-wy8xnba7eb.pdf

Design of efficient single-stage chirped pulse difference frequency generation at 7 μm, driven by a dual wavelength Ti:sapphire laser

We present a design for a high-energy single stage mid-IR difference frequency generation adapted to a two-color Ti:sapphire amplifier system. The optimized mixing process is based on chirped pulse difference frequency generation (CP-DFG), allowing for a higher conversion efficiency, larger bandwidth and reduced two photon absorption losses. The numerical start-to-end simulations include stretching, chirped pulse difference frequency generation and pulse compression. Realistic design parameters for commercially available non linear crystals (GaSe, AgGaS2, LiInSe2, LiGaSe2) are considered. Compared to conventional un-chirped DFG directly pumped by Ti:sapphire technology we report a threefold increase of the quantum efficiency. Our CP-DFG scheme provides up to 340 {\mu}J pulse energy directly at 7.2 {\mu}m when pumped with 3 mJ and supports a bandwidth of up to 350 nm. The resulting 240 fs mid-IR pulses are inherently phase stable.

/pdf/design-of-efficient-single-stage-chirped-pulse-difference-4osuqt442j.pdf

Christian Erny

Papers

Hydrogen‐Bond‐Directed Orientation in Nonlinear Optical Thin Films

Generation of broadband THz pulses in organic crystal OH1 at room temperature and 10 K

Generation of broadband THz pulses in organic crystal OH1 at room temperature and 10 K

Design of efficient single-stage chirped pulse difference frequency generation at 7 μm, driven by a dual wavelength Ti:sapphire laser

Design of efficient single stage chirped pulse difference frequency generation at 7 {\mu}m driven by a dual wavelength Ti:sapphire laser