Push-pull molecules

Luo Y, Norman P, Macak P, Agren H (2000) Solvent-induced two-photon absorption of a push — pull molecule. J Phys Chem A 104 4718-4722... 

The insertion of a photosensitive group or of a redox active unit into the push-pull system 1 yields switchable molecular wires and push-pull molecules that contain a photo-switch or a redox switch S, as represented in 4. Compounds of such type containing for instance electroactive ferrocene groups and photosensitive metal complexes, have been synthesized. Some of them are shown in series 5 (Marczinke, B. Przibilla, K.J. Lehn, J.-M., unpublished data). 

Thakkar and his group have completed many careful studies of intracules, extracules, Coulomb holes, and related topics.145 These position-space results are complemented by Thakkar s many studies of momentum densities and related quantities. He also has a long-standing interest in electron and X-ray scattering.146 His current interests include the relationship147 between the aromaticity of heterocyclic compounds and their polarizabilities, and the prediction of push-pull molecules that have a large nonlinear optical response and are thus candidates for materials to be used in optical computers. 

Specific Interactions in Solid State Dimers of Push-Pull Molecules Motivations and Model... 

Apart from the class of push-pull molecules many other polyconjugated systems exhibit peculiar electronic properties which make them very attractive for technological applications. Most of these systems do not posses a permanent dipole moment and their mutual interactions are due only to London dispersion forces. Also in this case, however,... 

The simplest model consists of two centres, one donor (D) and one acceptor (A), separated by a distance I and contains two electrons. Here we consider this simple system to illustrate some general relations between charge transfer, transition intensities and linear as well as non-linear optical polarizabilities. We will show below that the electro-optic parameters and the molecular polarizabilities may be described in terms of a single parameter, c, that is a measure of the extent of coupling between donor and acceptor. Conceptually, this approach is related to early computations on the behaviour of inorganic intervalence complexes (Robin and Day, 1967 Denning, 1995), Mulliken s model for molecular CT complexes (Mulliken and Pearson, 1969) and a two-form/two-state analysis of push-pull molecules (Blanchard-Desce and Barzoukas, 1998). 

Fig. 4. Schematics of push-pull molecules for electro-optic and photorefractive applications...

Fig. 5. Ground state and first excited state of a push-pull molecule...

Barzoukas, M., Runser, C., Port, A., Blanchard-Desce, M. A two-state description of (hyper) polarizabilities of push-pull molecules based on a two-form model. Chem. Phys. Lett. 257, 531-537 (1996)... 

Bishop, D.M., Champagne, B., Kirtman, B. Relationship between static vibrational and electronic hyperpolarizabilities of rr-conjugated push-pull molecules within the two-state valence-bond charge-transfer model. J. Chem. Phys. 109, 9987-9994 (1998)... 

Blanchard-Desce, M., Barzoukas, M. Two-form two-state analysis of polarizabilities of push-pull molecules. J. Opt. Soc. Am. B 15, 302-307 (1998)... 

Abstract The first part of this review presents the state of the art on two-photon absorbing molecules. Early works concerned the optimization of dipolar push-pull molecules. Recently, the synthesis of linear and branched centrosymmetrical quadrupolar molecules led to higher nonlinearities, but still far from reaching the fundamental limits of molecular two-photon cross-sections. 

Linear organic molecules were firstly considered for the design of TPA efficient molecules. This family can be divided into two groups (Fig. 1) (1) dipolar molecules constituted by a noncentrosymmetric structure, with a linear delocaUzed electrons system substituted at each end by electron donor D and acceptor groups A (push-pull molecules) (2) quadrupolar systems, consisting of symmetric molecules with a n electrons system substituted by donor or acceptor groups. 

In good agreement with the model described in Fig. 2b for push-pull molecules, TPA spectra match one-photon absorption curves this confirms that the value of cttpa is dominated by the dipolar term of Eq. 5 and that dipolar molecules efficient in quadratic NLO processes (see Eq. 6) should present high TPA responses. This trend has been illustrated by work on azo-aromatic... 

Fig. 4 Example of the relationship between molecular structure/TPA efficiency in push-pull molecules containing pyridyl and biphenyl amino moieties aTPA( max) in THE is expressed in GM for a laser excitation at 800 nm, and the linear absorption is in nm...

Cationic complexes of cyclometallated Ir (ppy)2 (ppy = 2-phenylpyridine) with chelated diimine ligands, such as bipyridines (bipy) and phenan-throlines (phen), have interesting phosphorescent properties with potential applications in electroluminescent devices. Such compounds show at rather high energy MLCT transitions (2,nax = 340-380 nm) from the [Ir° (ppy)2]-based HOMOs to the LUMOs based on the n -orbitals of the phen (or bipy) ligands. Thus, these complexes can be considered as push-pull molecules in which the Ir° (ppy)2 moiety acts as the donor and the diimine as the acceptor part. 

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