Symmetry Breaking in Pyrrolo[3,2-b]pyrroles: Synthesis, Solvatofluorochromism and Two-photon Absorption

Five centrosymmetric and one dipolar pyrrolo[3,2-b]pyrroles, possessing either two or one strongly electron-withdrawing nitro group have been synthesized in a straightforward manner from simple building blocks. For the symmetric compounds, the nitroaryl groups induced spontaneous breaking of inversion symmetry in the excited state, thereby leading to large solvatofluorochromism. To study the origin of this effect, the series employed peripheral structural motifs that control the degree of conjugation via altering of dihedral angle between the 4-nitrophenyl moiety and the electron-rich core. We observed that for compounds with a larger dihedral angle, the fluorescence quantum yield decreased quickly when exposed to even moderately polar solvents. Reducing the dihedral angle (i.e., placing the nitrobenzene moiety in the same plane as the rest of the molecule) moderated the dependence on solvent polarity so that the dye exhibited significant emission, even in THF. To investigate at what stage the symmetry breaking occurs, we measured two-photon absorption (2PA) spectra and 2PA cross-sections (sigma(2PA)) for all six compounds. The 2PA transition profile of the dipolar pyrrolo[3,2-b]pyrrole, followed the corresponding one-photon absorption (1PA) spectrum, which provided an estimate of the change of the permanent electric dipole upon transition, approximate to 18D. The nominally symmetric compounds displayed an allowed 2PA transition in the wavelength range of 700-900nm. The expansion via a triple bond resulted in the largest peak value, sigma(2PA)=770GM, whereas altering the dihedral angle had no effect other than reducing the peak value two- or even three-fold. In the S0S1 transition region, the symmetric structures also showed a partial overlap between 2PA and 1PA transitions in the long-wavelength wing of the band, from which a tentative, relatively small dipole moment change, 2-7D, was deduced, thus suggesting that some small symmetry breaking may be possible in the ground state, even before major symmetry breaking occurs in the excited state.1111Ysciescopu

Proposal for a Practical Wizard of Physical Training Instructor's Administration in the Czech Army

Název: Návrh praktického průvodce administrativní činnosti tělovýchovného pracovníka AČR English name: Proposal for a practical wizard of physical training instructor's administration in the Czech Army Cíl práce: Analýza administrativní činnosti tělovýchovných pracovníků AČR a navržení optimálního řešeni pro tvorbu praktického průvodce. Metoda: Návrh byl zpracován na základě obsahové analýzy a komparace dokumentů vytvořených tělovýchovnými pracovníky AČR. Celkem bylo dodáno so88 dokumentů (vyjádřeno objemově 2,J Gb dat) v nejrůznějších formátech (převážně .doc a .xls). Pro orientaci v datech byly dokumenty roztříděny deduktivní metodou. Strukturní analýzou dokumentů byly do- kumenty rozděleny do oblastí. Na závěr byla provedena deskripce obsahu dokumentů. Výsledky: Na základě analýzy dostupných možnosti tělovýchovných pra- covníků při práci s výpočetní technikou a analýze vhodných softwarových nástrojů byl navržen způsob řešeni vzorových dokumentů a možné varianty praktického průvodce administrativní činnosti. Průvodce byl vytvořen v kódováni HTML (vybráno jako vhodnější řešeni) a v programu Zoner Con- text 4 (ukázka řešeni). Klíčová slova: vojenská tělovýchova, tělovýchovný pracovník AČR, admi- nistrativní činnost, formuláře, praktický průvodce administrativní činnosti

Theoretical spectroscopy of a NIR-absorbing benziphthalocyanine dye

Benziphthalocyanines are (Yanai et al. in Chem Phys Lett 393:51-57, 2004) phthalocyanines in which one isoindoline unit has been replaced by a phenyl ring. In this study, we focus on a macrocycle of this family recently synthesized by Uchiyama and co-workers (Toriumi et al. Angew Chem Int Ed 53:7814-7818, 2014), and composed of three indoline units (substituted with 2,6-diisopropylphenyl-oxy groups) and one resorcinol unit. We aim at characterizing the possible tautomers to evaluate whether this compound might exist as a mixture of several forms or not. To reach our goals, we use state-of-the-art ab initio theories, i.e., Time-Dependent Density Functional Theory coupled with a refined solvation model (the Polarizable Continuum Model) as well as post-Hartree Fock approaches. We first investigate the stability, the structure and the aromaticity of the possible tautomers before analyzing their spectroscopic signatures. Using an approach going beyond the vertical approximation, we compare experimental and theoretical 0-0 energies and band shapes. This study allows us to point out the dominant presence of the quinoidal form as well as to unravel the vibronic contributions responsible for the specific shape of the optical spectrum

Highly fluorescent extended 2-(2 `-hydroxyphenyl)benzazole dyes: synthesis, optical properties and first-principle calculations

The investigation of the optical properties of extended 2-(2-hydroxyphenyl)benzazole dyes showed a complete frustration of the excited-state intramolecular proton transfer (ESIPT) process leading to a novel family of highly fluorescent fluorophores. In the case of a benzothiazole ring, restoration of ESIPT can be observed in acidic medium leading to ratiometric sensing. These experimental results have been rationalised by first-principle calculations

Modelling excitation energy transfer in covalently linked molecular dyads containing a BODIPY unit and a macrocycle

With the help of time-dependent density functional theory coupled to an implicit solvation scheme (the polarisable continuum model), we have investigated the singlet-singlet Excitation Energy Transfer (EET) process in a panel of large BODIPY-macrocycle dyads. We have first considered different strategies to compute the electronic coupling in a representative BODIPY-zinc porphyrin assembly and, next evaluated the performances of the chosen computational protocol on several BODIPY-porphyrinoid molecular architectures for which the EET rate constants have been experimentally measured. This step showed the robustness of our approach, which is able to reproduce the magnitude of the measured rate constants in most cases. We have finally applied the validated methodology on newly designed dyads combining a BODIPY unit and an azacalixphyrin macrocycle, a recently synthesised porphyrin analogue that displays exceptional optical properties. This work allowed us to propose new molecular architectures presenting improved properties and also to highlight the interest of using azacalixphyrin as a building block in molecular light-harvesting antennas

Tuning ESIPT fluorophores into dual emitters

International audienceDyes undergoing excited-state intramolecular proton transfer (ESIPT) are known to present large Stokes shifts as a result of the important geometrical reorganisation following photon absorption. When the ESIPT process is not quantitative, one can obtain dual emitters characterised by two distinct fluorescence bands, observed due to emissions from both the canonical and ESIPT isomers. However, dual emission generally requires to maintain a very specific balance, as the relative excited-state free energies of the two tautomers have to be within a narrow window to observe the phenomenon. Consequently, simple chemical intuition is insufficient to optimise dual emission. In the present contribution, we investigate, with the help of quantum-mechanical tools and more precisely, time-dependent density functional theory (TD-DFT) and algebraic diagrammatic construction (ADC), a wide panel of possible ESIPT/dual emitters with various substituents. The selected protocol is first shown to be very robust on a series of structures with known experimental behaviour, and next is applied to novel derivatives with various substituents located at different positions. This work encompasses the largest chemical library of potential ESIPT compounds studied to date. We pinpoint the most promising combinations for building dual emitters, highlight unexpected combination effects and rationalise the impact of the different auxochromes

Synthesis and Photophysical Properties of N-Arylated Diketopyrrolopyrroles

The N-arylation of diketopyrrolopyrroles with aryl fluorides free of nitro groups was successfully achieved for the first time. Diketopyrrolopyrroles possessing 3,4-dimethoxyphenyl and benzofuryl substituents underwent reaction with, for example, pentafluoropyridine, in the presence of K2CO3 in N-methyl-2-pyrrolidone to give the desired products in moderate yields. Their photophysical properties in solution were found not to differ significantly from those of analogous N-alkylated diketopyrrolopyrroles, whereas in contrast to the latter compounds, they were found to possess fluorescence in the solid state. The photophysical properties of all compounds were rationalized by using time-dependent density functional theory

Fused Bis-Azacalixphyrin that reaches NIR II absorptions

International audienc

Symmetry Breaking in Pyrrolo[3,2-b]pyrroles: Synthesis, Solvatofluorochromism and Two-photon Absorption

Five centrosymmetric and one dipolar pyrrolo[3,2-b]pyrroles, possessing either two or one strongly electron-withdrawing nitro group have been synthesized in a straightforward manner from simple building blocks. For the symmetric compounds, the nitroaryl groups induced spontaneous breaking of inversion symmetry in the excited state, thereby leading to large solvatofluorochromism. To study the origin of this effect, the series employed peripheral structural motifs that control the degree of conjugation via altering of dihedral angle between the 4-nitrophenyl moiety and the electron-rich core. We observed that for compounds with a larger dihedral angle, the fluorescence quantum yield decreased quickly when exposed to even moderately polar solvents. Reducing the dihedral angle (i.e., placing the nitrobenzene moiety in the same plane as the rest of the molecule) moderated the dependence on solvent polarity so that the dye exhibited significant emission, even in THF. To investigate at what stage the symmetry breaking occurs, we measured two-photon absorption (2PA) spectra and 2PA cross-sections (sigma(2PA)) for all six compounds. The 2PA transition profile of the dipolar pyrrolo[3,2-b]pyrrole, followed the corresponding one-photon absorption (1PA) spectrum, which provided an estimate of the change of the permanent electric dipole upon transition, approximate to 18D. The nominally symmetric compounds displayed an allowed 2PA transition in the wavelength range of 700-900nm. The expansion via a triple bond resulted in the largest peak value, sigma(2PA)=770GM, whereas altering the dihedral angle had no effect other than reducing the peak value two- or even three-fold. In the S0S1 transition region, the symmetric structures also showed a partial overlap between 2PA and 1PA transitions in the long-wavelength wing of the band, from which a tentative, relatively small dipole moment change, 2-7D, was deduced, thus suggesting that some small symmetry breaking may be possible in the ground state, even before major symmetry breaking occurs in the excited state

Traitement de la grenouillette sus-hyoidienne

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