An efficient and expeditious synthesis of di- and trisubstituted amino-phenyl and -benzyl derivatives of tetrazole and [1,3,4]oxadiazol-2-one

A practical protocol for the parallel synthesis and purification of amino tetrazole and [1,3,4]oxadiazol-2-one derivatives as carboxylic acid bioisosteres is described. Phenyl- and benzyl-amines, substituted with tetrazole or [1,3,4]oxadiazol-2-one, were transformed into functionally diverse and novel compounds, with p K a values ranging from 4.9 to 8.4, by two sequential reductive alkylation reactions. These series of di- and trisubstituted amino-phenyl and -benzyl derivatives were produced in solution using solid-supported reagents and were purified by solid-phase extraction (SPE) techniques.     

Polaritons in confined systems

Polaritons in confined systems are introduced and their dispersion is calculated. The amount of squeezing of confined excitons-polaritons in GaAs quantum wells is evaluated.     

Optical properties of microcavity polaritons

This work contains a theoretical analysis of the optical properties of semiconductor quantum wells embedded in planar Fabry-Perot microcavities. In particular, the properties of the system in correspondence to the excitonic transition are studied by means of the polariton formalism. The polariton states in microcavities are derived and the polar-iton dispersion is presented. Particular emphasis is put on the existence of two well distinct regimes depending on the exciton and cavity parameters: strong coupling and weak coupling regime. The main experimental results are reviewed and compared with the prediction of the theory. After the polariton states have been characterized, the optical response of the system is discussed, with particular attention to the photoluminescence measurements. The polariton formation and relaxation through phonon scattering and the effect of the exciton inhomogeneous broadening are considered and, finally, a phe-nomenological model for the polariton photoluminescence spectra is presented.     

Regioselective synthesis of 2,8-disubstituted 4-aminopyrido[3,2-d]pyrimidine-6-carboxylic acid methyl ester compounds

We report herein the synthesis of 4-amino-2,8-dichloropyrido[3,2-d]pyrimidine derivatives 2 and their regioselective diversification through S(N)Ar and metal-catalyzed cross-coupling reactions. While amination of 2 took place selectively at C-2, the regioselectivity of thiol or thiolate addition depended on the reaction conditions. Selective C-8 addition was obtained in DMF with Hünig's base and C-2 addition in (i)PrOH. These C-2 or C-8 regioselective thiolations provided an opportunistic way to selectively activate either of the two positions toward the metal-catalyzed cross-coupling reaction. The chloride could be efficiently substituted by Suzuki-Miyaura reaction and the sulfanyl group by Liebeskind-Srogl cross-coupling reaction, demonstrating the orthogonality of both reactive centers. The development of regioselective conditions for these different transformations yielded the synthesis of 4-amino-2,6,8-trisubstituted pyrido[3,2-d]pyrimidine derivatives, with various substituents.     

Microscopic quantum theory of exciton polaritons with spatial dispersion

Summary The quantum Hamiltonian of excitons in interaction with the electromagnetic field is derived for the case of Frenkel excitons and for the case of Wannier excitons by taking into account spatial dispersion and the singular behaviour of the electron-hole exchange. The exact eigenvalues and eigenstates are obtained for the upper and lower polaritons. In the case of Wannier excitons a correction to the phenomenological quantum theory is found. In both cases the coincidence of the upper polariton limit fork=0 and the longitudinal exciton value atk=0 is proved. Spin effects are shown to introduce a factor two both in the coupling strength and in the transverse-longgitudinal splitting for singlet excitons.

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Riassunto Si deriva l’hamiltoniana quantistica di eccitoni in interazione con il campo elettromagnetico sia nel modello di Frenkel che nel modello di Wannier, includendo la dispersione spaziale e la singolarità del termine di scambio elettrone-buca. Si ottengono autostati e autovalori esatti per il polaritone superiore e quello inferiore. Nel modello di Wannier si trova una correzione alla teoria quantistica fenomenologica. In entrambi i modelli si dimostra la coincidenza del limite ak=0 del polaritone superione con quello dell’eccitone longitudinale. Questo è connesso con la dipendenza dell’accoppiamento eccitone-radiazione e dello scambio elettrone-buca dalla forza di oscillazione della transizione ottica. Gli effetti di spin introducono un fattore due sia nel termine di accoppiamento che nella separazione longitudinale-trasversale di eccitoni di singotetto.

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Резуме Квантовый Гамильтоньян зкцитонов, взаимодействующих с злектромагнитным полем, получен и в случае зкцитонов Френкеля и в случае зкцитонов Ванниера, причем учитывается пространственная дисперсия и особое поведение злектронно-дырочного обмена. Получены точные собственные значения и точные собственные функции Гамильтоньяна. В случае зкцитонов Ванниера найдена поправка результатов, полученных в феноменологической кватовой теории. В обоих случаях доказывается совпад ение энергии верхнего поларитона приk=0 с знергиейпродольного зкцитона приk=0. Доказывается, что наличие спина вызывает удвоение козффициента силы связи и также удвоение поперечно-продоьного расщепления синглетных состояний.

     

Access and regioselective transformations of 6-substituted 4-aryl-2,8-dichloropyrido[3,2-d]pyrimidine compounds

We report herein an efficient route for the synthesis of 2,4,8-trichloropyrido[3,2-d]pyrimidines 1 with R(1) substituents at C-6. The potential of such scaffolds was demonstrated by the possibility to displace regioselectively each aromatic chloride to introduce diversity. Sequential sulfur nucleophilic addition followed by Liebeskind-Srogl cross-coupling reaction yielded unprecedented aryl introduction at C-4 on a trichloropyrido[3,2-d]pyrimidine derivative. The reactivity difference of the remaining two chlorides toward S(N)Ar reactions was investigated. Amination yielded high C-2 regioselectivity, while thiolation was influenced by C-6 substituents, resulting in medium to high C-2 versus C-8 regioselectivity. The last chloride was efficiently displaced by S(N)Ar, Suzuki-Miyaura cross-coupling reaction, or reduction. C-2 arylation as a final step was also possible by Liebeskind-Srogl cross-coupling reaction on the previously introduced C-2 thioether. A concise and highly divergent synthetic use of 1 was developed, thereby providing an efficient approach to explore the structure-activity relationship of pyrido[3,2-d]pyrimidine derivatives such as 9, 10, 15, and 16.     

Statistical properties of polariton states

Summary The unitary transformation that relates free polarization and photon states to polariton states is constructed. The time evolution of an arbitrary initial state in terms of the polariton Hamiltonian is presented. The many-photon components of polariton states as well as the transition probabilities to polariton states and the intrinsec and time-dependent polariton squeezing are discussed.     

Wärmewiderstand durch Spinwellen —Spinwellenstreuung in einem Ferromagnetikum

The heat conduction by spin waves is obtained using the Boltzmann equation and considering only magnon-magnon scattering. In contrast to the case of phonons with a linear energy-momentum relationship, Umklapp processes need not be considered to obtain a non-vanishing collision-term in the Boltzmann equation for magnons. In a spin system with a Hamiltonian consisting of exchange and anisotropy energies the temperature dependence of the thermal resistivity isa+bT ^3/2 within the spin wave approximation.     

Strongly driven exciton resonances in quantum wells: light-induced dressing versus coulomb scattering

The nonequilibrium dynamics of a two-dimensional electron-hole gas is studied in the regime of strong and resonant pumping of the exciton resonance. The Coulomb collision rates are consistently determined by taking into account the light-induced coherence of the two-band system that leads to a dressing of the carrier spectral functions. The light dressing dramatically reduces the Coulomb scattering efficiency. Results are presented for Rabi oscillations in the time domain and dynamical Stark splitting in the pump-probe absorption spectra.