960 research outputs found
Thermal equilibration between excited states or solvent effects: unveiling the origins of anomalous emissions in heteroleptic Ru(II) complexes
In this manuscript we present a computational study on the photoluminescence
properties of several heteroleptic [Ru(H)(CO)(N^N)(tpp)2]+ complexes (tpp =
triphenylphosphine). A special focus is set on disentangling the
temperature-dependent emissive properties. Experimentally, when cooling a
solution of [Ru(H)(CO)(dmphen)(tpp)2]+ (dmphen =
5,6-dimethyl-1,10-phenanthroline) from room to cryogenic temperature, a partial
emission switch from metal-to-ligand charge transfer (3MLCT) to ligand-centered
(3LC) phosphorescence is observed, resulting in dual photoluminescence. Two
different origins of the anomalous emissions are possible, i.e., thermal
equilibration between electronically excited states or different excited state
solvent relaxation effects. Our calculations are in favor of the thermally
equilibrated scenario. This computational investigation highlights the
importance of controlling the temperature-dependent emissive behavior for
optoelectronic applications
General Approach To Compute Phosphorescent OLED Efficiency
Phosphorescent organic light-emitting diodes (PhOLEDs) are widely used in the
display industry. In PhOLEDs, cyclometalated Ir(III) complexes are the most
widespread triplet emitter dopants to attain red, e.g., Ir(piq)3 (piq =
1-phenylisoquinoline), and green, e.g., Ir(ppy)3 (ppy = 2-phenylpyridine),
emissions, whereas obtaining operative deep-blue emitters is still one of the
major challenges. When designing new emitters, two main characteristics besides
colors should be targeted: high photostability and large photoluminescence
efficiencies. To date, these are very often optimized experimentally in a
trial-and-error manner. Instead, accurate predictive tools would be highly
desirable. In this contribution, we present a general approach for computing
the photoluminescence lifetimes and efficiencies of Ir(III) complexes by
considering all possible competing excited-state deactivation processes and
importantly explicitly including the strongly temperature-dependent ones. This
approach is based on the combination of state-of-the-art quantum chemical
calculations and excited-state decay rate formalism with kinetic modeling,
which is shown to be an efficient and reliable approach for a broad palette of
Ir(III) complexes, i.e., from yellow/orange to deep-blue emitters
A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Bicyclic Systems
Pursuing our efforts to define highly-accurate estimates of the relative
energies of excited states in organic molecules, we investigate, with
coupled-cluster methods including iterative triples (CC3 and CCSDT), the
vertical excitation energies of 10 bicyclic molecules (azulene, benzoxadiazole,
benzothiadiazole, diketopyrrolopyrrole, fuofuran, phthalazine, pyrrolopyrrole,
quinoxaline, tetrathiafulvalene, and thienothiophene). In total, we provide
\emph{aug}-cc-pVTZ reference vertical excitation energies for 91 excited states
of these relatively large systems. We use these reference values to benchmark
various wave function methods, i.e., CIS(D), EOM-MP2, CC2, CCSD, STEOM-CCSD,
CCSD(T)(a)*, CCSDR(3), CCSDT-3, ADC(2), ADC(2.5), ADC(3), as well as some
spin-scaled variants of both CC2 and ADC(2). These results are compared to
those obtained previously on smaller molecules. It turns out that while the
accuracy of some methods is almost unaffected by system size, e.g., CIS(D) and
CC3, the performance of others can significantly deteriorate as the systems
grow, e.g., EOM-MP2 and CCSD, whereas others, e.g., ADC(2) and CC2, become more
accurate for larger derivatives.Comment: 19 pages, 2 figure
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Mise au point de méthodes de chimie quantique pour optimiser la géométrie des polymères stéréoréguliers
Elaboration de procédés de chimie quantique pour évaluer les hyperpolarisabilités de polymères stéréoréguliers
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Aza-boron-dipyrromethene dyes: TD-DFT benchmarks, spectral analysis and design of original near-IR structures
International audienceThe excited-state energies of aza-boron-dipyrromethene (Aza-BODIPY) derivatives are investigated with Time-Dependent Density Functional Theory (TD-DFT), with twin goals. On the one hand, a pragmatic, yet efficient, computational protocol is defined in order to reach rapidly semi-quantitative estimates of the λmax of these challenging dyes. It turned out that a PCM-TD-BMK/6-311+G(2d,p)//PCM-PBE0/6-311G(2d,p) approach delivers appropriate lower bounds of the experimental results, despite the inherent limits of the vertical approximation. On the other hand, the method is applied to design new dyes absorbing in the near-IR. The spectral features of ca. 30 new compounds have been simulated in a systematic way, trying to efficiently combine several available synthetic strategies leading to significant bathochromic displacements. A series of dyes absorbing above 850 nm are proposed, illustrating that (relatively) fast theoretical calculations might be a useful pre-screening step preceding synthesis
Optical signatures of borico dyes: a TD-DFT analysis
International audienceUsing time-dependent density functional theory, we investigate the excited-state properties of a series of emissive dyes combining the properties of coumarins and fluoroborate compounds. These boron-iminocoumarins (borico) compounds have been synthesized very recently by Frath et al. (Chem Commun 49:4908, 2013) . We determine both their vertical and 0-0 energies, reproduce and analyze their characteristic experimental band shape, investigate the nature of the excited-states in large dyads containing two different fluoroborate complexes and design red-shifted compounds. We also consider an additional panel of fused coumarin-BODIPY emitters
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