Modular synthesis of zwitterionic, xanthene bridged, low twist angle chromophores with high hyperpolarizability (original) (raw)
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Entrapping of Push-Pull Zwitterionic Chromophores in Hybrid Matrices for Photonic Applications
Journal of Sol-gel Science and Technology, 2003
A new class of heterocycle-based push-pull chromophores showing enhanced nonlinear properties characterized by an aromatic and highly zwitterionic ground state and a quinoid/neutral excited state have been synthesized to be incorporated in sol-gel hybrid systems. This class of compounds shows very large first molecular hyperpolarizabilities (ßµ as high as 27000 × 10-48 esu) and is a promising candidate for photonic
Journal of the American Chemical Society, 2007
This contribution details the synthesis and chemical/physical characterization of a series of unconventional twisted π-electron system electro-optic (EO) chromophores. Crystallographic analysis of these chromophores reveals large ring-ring dihedral twist angles (80-89°) and a highly charge-separated zwitterionic structure dominating the ground state. NOE NMR measurements of the twist angle in solution confirm that the solid-state twisting persists essentially unchanged in solution. Optical, IR, and NMR spectroscopic studies in both the solution phase and solid state further substantiate that the solid-state structural characteristics persist in solution. The aggregation of these highly polar zwitterions is investigated using several experimental techniques, including concentration-dependent optical and fluorescence spectroscopy and pulsed field gradient spin-echo (PGSE) NMR spectroscopy in combination with solidstate data. These studies reveal clear evidence of the formation of centrosymmetric aggregates in concentrated solutions and in the solid state and provide quantitative information on the extent of aggregation. Solution-phase DC electric-field-induced second-harmonic generation (EFISH) measurements reveal unprecedented hyperpolarizabilities (nonresonant µ as high as -488 000 × 10 -48 esu at 1907 nm). Incorporation of these chromophores into guest-host poled polyvinylphenol films provides very large electrooptic coefficients (r33) of ∼330 pm/V at 1310 nm. The aggregation and structure-property effects on the observed linear/nonlinear optical properties are discussed. High-level computations based on state-averaged complete active space self-consistent field (SA-CASSCF) methods provide a new rationale for these exceptional hyperpolarizabilities and demonstrate significant solvation effects on hyperpolarizabilities, in good agreement with experiment. As such, this work suggests new paradigms for molecular hyperpolarizabilities and electro-optics. Steier, W. H.; Robinson, B. H.; Zhang, C.; Ren, A.; Garner, S.; Chen, A.; Londergan, T.; Irwin, L.; Carlson, B.; Fifield, L.; Phelan, G.; Kincaid, C.; Amend, J.; Jen, A. Houbrechts, S.; Kauranen, M.; Clays, K.; Persoons, A.
Chemistry of Materials, 2006
The electric-field-dependent change in refractive index in nonlinear optical (NLO) materials can be utilized for electrical-to-optical signal conversion, such as fast electrooptic (EO) modulators needed in optical telecommunication. 1 Compared to inorganic NLO crystals (e.g., LiNbO 3 ), organic NLO materials offer advantages such as higher EO coefficients, lower dielectric constants, and good processibility. 2 To obtain a large EO response, chromophores with a high molecular nonlinearity (hyperpolarizability ) need to be oriented to form a macroscopically noncentrosymmetric material. For chromophores with a large dipole moment (µ), one way to achieve such a polar ordering is by electric-field poling of the chromophores in a polymer matrix. Consequently, the main figure of merit describing the performance of NLO chromophores in such EO polymer applications is the scalar product µ . Among many types of organic NLO chromophores, zwitterionic derivatives of 7,7,8,8-tetracyanoquinodimethane (TCNQ) such as (Z)-4-[1-cyano-3-(diethylamino)-2-propenylidene]-2,5-cyclohexadiene-1-ylidenepropanedinitrile (DEMI; ) are known to possess very high molecular hyperpolarizabilities and show the largest µ values reported to date. 3 To be useful for EO applications, the chromophores need to be either doped in a medium (e.g., polymer or sol-gel glass) or covalently linked to a polymer and oriented under an electric field. While the zwitterionic nature of the NLO chromophores is in favor of attaining a large µ value, it can also present limitations for EO applications as a result of poor solubility and strong dipole-dipole interactions. For example, DEMI was reported to have a high µ 0 value of 9500 × 10 -48 esu ( 0 ) static hyperpolarizability). 3 An analogue, picolinium quinodimethane (PQDM) 2a ( , was calculated to have a static molecular hyperpolarizability of 1270 × 10 -30 esu. 4 However, both chromophores are highly crystalline and have no functional groups (e.g., OH or NH 2 ), making it very difficult to either physically or chemically incorporate them into a host polymer.
2015
Since 2005, the Diederich group has conducted comprehensive research to develop nonplanar push-pull chromophores possessing significant optoelectronic properties (Chapter 1). Formal [2+2] cycloaddition-retroelectrocyclization (CA-RE) reactions have been utilized to accomplish this synthetic goal. In the last ten years, most of our studies have addressed the reactions of commonly used tetracyanoethene (TCNE) or 7,7,8,8tetracyano-p-quinodimethane (TCNQ) with activated alkynes. However, there are only a few reports exploring the possibility of altering the acceptor molecule for these reactions. To tackle this issue, we introduced 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an electron-deficient alkene moiety in formal [2+2] CA reactions (Chapter 2). Surprisingly, the chosen alkene was not suitable to undergo RE following initial CA. Attempts to force the RE instead resulted in an unexpected rearrangement whereby the spirocyclic push-pull chromophores were obtained.
Exceptional Molecular Hyperpolarizabilities in Twisted π-Electron System Chromophores
Angewandte Chemie International Edition, 2005
Molecule-based electrooptic (EO) materials are of intense research interest for understanding how light interacts with matter and for applications in photonic technologies such as high-speed optical communications, integrated optics, and optical data processing and storage. In such materials, the second-order susceptibility tensor governing EO response (r 33 ), is governed both by the net polar microstructural order and the microscopic molecular first hyperpolarizability tensor (b). Large b values are essential for large EO response, and the quest for higher performance EO chromophores presents a daunting challenge. To date, effective chromophores have been designed according to similar principles embodied in the classical "two-level" model: conjugated p systems endcapped with donor (D) and acceptor (A) moieties. Elegant efforts have sought maximum b by optimizing D and A strengths and conjugation pathways, [3] directed by "bond length alternation" and "auxiliary donor and acceptor" models. Such strategies utilize extended planar p-conjugation, resulting in chromophores that are inherently elaborate structurally, complicating synthesis and introducing potential chemical, thermal, and photochemical instabilities. Alternative routes to very large-b chromophores would clearly be desirable, and there is growing evidence that simple two-level systems may not provide access. Recent theoretical work suggests that unconventional chromophores with twisted p-electron systems bridging D and A substituents (TICTOID = twisted intramolecular chargetransfer; Scheme 1) may exhibit unprecedented hyperpolarizabilities through non-classical mechanisms. These would have relatively simple biaryl structures in which b is sterically tunable through R 1 , R 2 modification of the interplanar dihedral angle (q). Large b magnitudes are predicted at q % 70-858, [8a] with twist-induced reduction in D-p-A conjugation leading to charge-separated zwitterionic ground states. The intriguing question is whether such molecules, with small numbers of p-electrons, could thereby exhibit far larger b values than conventional planar chromophores.
TURKISH JOURNAL OF CHEMISTRY, 2021
Introduction Donor-π-acceptor (D-π-A)-type push-pull chromophores, are well-known for their desirable features, such as tunable strong intramolecular charge-transfer bands that absorb light in a wide range of area including visible and near-IR regions, spectacular nonlinear optical properties, excellent solubility, and high thermal stabilities [1-3]. With these desired properties, push-pull chromophores have already been employed in a series of advanced applications such as photovoltaics, [4,5] light-emitting diodes, [6,7] sensors, [1,8,9] and NLO devices [1,10,11]. The successful integration of push-pull systems in high technology areas makes it necessary to design and synthesize new molecular structures with enhanced optoelectronic properties. However, synthetic strategies to access these entities are arguably limited and require multi-step protocols. The formal [2+2] cycloaddition-retroelectrocyclization (CA-RE) is one of the promising reaction candidates to circumvent these synthetic problems [1]. With its high-yielding nature and broad substrate scope, [2+2] CARE transformation occurs under very mild conditions without requiring a catalyst and fulfills all the requirements to be referred as a "click-type reaction" [12,13] [2+2] CARE transformation requires electron-rich alkynes and electrondeficient alkenes to synthesize nonplanar D-π-A systems [1]. Bruce and co-workers reported the first example of [2+2] CARE reactions between ruthenium-substituted acetylides and tetracyanoethylene (TCNE) in 1981 [14]. Later, metalfree substrates have also been employed in CARE reactions for the synthesis of structurally demanding push-pull chromophores by Diederich and co-workers [11]. The short and easy-to-perform CARE method has increased the variety in the design of the target push-pull chromophores. When the structures of push-pull chromophores obtained by CARE reactions are examined in detail, derivatization is mostly made in two main parts (donor groups and acceptor groups).
The Journal of Physical Chemistry C, 2008
The synthesis, structural and spectroscopic characterization, and nonlinear optical response properties of a "slightly" twisted zwitterionic 4-quinopyran electrooptic chromophore FMC, 2-{4-[1-(2-propylheptyl)-1Hpyridine-4-ylidene]cyclohexa-2,5-dienylidene}malononitrile, are reported. X-ray diffraction data and density functional theory (DFT) minimized geometries confirm that deletion of the four o-, o′-, o′′-, and o′′′-methyl groups in the parent chromophore TMC-2, 2-{4-[3,5-dimethyl-1-(2-propylheptyl)-1H-pyridin-4-ylidene]-3,5dimethylcyclohexa-2,5-dienylidene}malononitrile, relaxes the arene-arene twist angle from 89.6 to 9.0°. These geometrical changes result in a significantly increased contribution of the quinoidal structure to the molecular ground state of FMC (versus TMC-2), reduced solvatochromic shifts in the optical spectra, and a diminished electric-field-induced second-harmonic (EFISH) generation derived molecular hyperpolarizability (µ ) -2340 × 10 -48 esu of DFMC, the dendrimer derivative of FMC, vs -24000 × 10 -48 esu of TMC-2) in CH 2 Cl 2 at 1907 nm. Pulsed field gradient spin-echo (PGSE) NMR spectroscopy and EFISH indicate that the levels of FMC aggregation in solution are comparable to those of TMC-2 (monomers and dimers) in CH 2 Cl 2 solution. B3LYP and INDO/S computation of chromophore molecular structure, aggregation, and hyperpolarizability trends are in good agreement with experiment. † Part of the "Larry Dalton Festschrift".
European Journal of Organic Chemistry, 2009
We have developed procedures for the synthesis of push-pull azo-chromophores containing the s-triazolo[3,4-b]thiadiazole heterocycle compatible with the presence of electron-acceptor groups (nitrophenyl group) as substituents on both the triazole and thiadiazole rings. The linear and non-linear optical properties of the synthesized chromophores have been characterized by the EFISH technique, electro-optical absorption spectroscopy and DFT calculations. The combined
Journal of the American Chemical Society, 2006
Efficient noncentrosymmetric arrangement of nonlinear optical (NLO) chromophores with high first-order hyperpolarizability () for increased electro-optical (EO) efficiency has proven challenging as strong dipolar interactions between the chromophores encourage antiparallel alignment, attenuating the macroscopic EO effect. This work explores a novel approach to simultaneously achieve large values while providing an adjustable dipole moment by linking a strong neutral-ground-state (NGS) NLO chromophore with positive to a zwitterionic (ZWI) chromophore with negative in an antiparallel fashion. It is proposed that the overall of such a structure will be the sum of the absolute values of the two types of chromophores while the dipole moment will be the difference. Molecules 1-3 were synthesized to test the feasibility of this approach. Molecular dynamics calculations and NMR data supported that the NGS chromophore component and the ZWI chromophore component self-assemble to an antiparallel conformation in chloroform. Calculations showed that the dipole moment of 1 is close to the difference of the two component chromophores. Hyper-Rayleigh scattering (HRS) studies confirmed that the first hyperpolarizability of 1 is close to the sum of the two component chromophores. These results support the idea that an antiparallel-aligned neutral-ground-state chromophore and a zwitterionic chromophore can simultaneously achieve an increase in and a decrease of the dipole moment.
Hybrid organic–inorganic materials containing poled zwitterionic push–pull chromophores
Journal of the European Ceramic Society, 2004
Dihydroxy functionalised zwitterionic push-pull chromophores have been introduced in 3-glycidoxypropyltrimethoxysilane, tetraethylorthosilicate and N-[(3-trimethoxysilyl)propyl]ethylenediamine derived hybrid materials. Hybrid films have been deposited as thick layers via spin-coating. The amine groups introduced with the organically modified alkoxide bearing amine functionalities have been found to have an effective scavenger effect of the dye photobleaching.The addition, during the synthesis of the precursor sol, of N-hydroxyl carbazole has allowed to reach up to 20% of chromophore concentration avoiding the formation of aggregates within the matrix. The NLO properties of the material, after poling, have shown a good temporal stability, with retention of ca. 70% of the initial signal value, after several months, providing a d 33 value of $ 50Ä70 pm V À1 at the wavelength of 1.064 mm.