Natural anthocyanin pigments/dyes and phenolic copigments/co-dyes form noncovalent complexes, which stabilize and modulate (in particular blue, violet, and red) colors in flowers, berries, and food products derived from them (including wines, jams, purees, and syrups). This noncovalent association and their electronic and optical implications constitute the copigmentation phenomenon. Over the past decade, experimental and theoretical studies have enabled a molecular understanding of copigmentation. This review revisits this phenomenon to provide a comprehensive description of the nature of binding (the dispersion and electrostatic components of π-π stacking, the hydrophobic effect, and possible hydrogen-bonding between pigment and copigment) and of spectral modifications occurring in copigmentation complexes, in which charge transfer plays an important role. Particular attention is paid to applications of copigmentation in food chemistry.

Thermally activated delayed fluorescence (TADF) offers the premise for all-organic light emitting diodes with quantum efficiencies competing those of transition metal-based phosphorescent devices. While computational efforts have so far largely focused on gas-phase calculations of singlet and triplet excitation energies, the design of TADF materials requires multiple methodological developments targeting among others a quantitative description of electronic excitation energetics, fully accounting for environmental electrostatics and molecular conformational effects, the accurate assessment of the quantum-mechanical interactions that trigger the elementary electronic processes involved in TADF, as well as a robust picture for the dynamics of these fundamental processes. In this perspective, we describe some recent progress along those lines and highlight the main challenges ahead for modeling, which we hope will be useful to the whole TADF community.

A new approach stemming from the adiabatic-connection (AC) formalism is proposed to derive parameter-free double-hybrid (DH) exchange-correlation functionals. It is based on a quadratic form that models the integrand of the coupling parameter, whose components are chosen to satisfy several well-known limiting conditions. Its integration leads to DHs containing a single parameter controlling the amount of exact exchange, which is determined by requiring it to depend on the weight of the MP2 correlation contribution. Two new parameter-free DHs functionals are derived in this way, by incorporating the non-empirical PBE and TPSS functionals in the underlying expression. Their extensive testing using the GMTKN30 benchmark indicates that they are in competition with state-of-the-art DHs, yet providing much better self-interaction errors and opening a new avenue towards the design of accurate double-hybrid exchange-correlation functionals departing from the AC integrand.

Articles you may be interested inExcited state calculations on fluorene-based polymer blends: Effect of stacking orientation and solvation Theoretical and experimental studies of the opto-electronic properties of positively charged oligo(phenylene vinylene)s: Effects of chain length and alkoxy substitutionWe report a detailed quantum-chemical characterization of the electronic and optical properties of polyfluorene chains and compare them to those in copolymers containing alternating fluorene and benzothiadiazole or ethylenedioxythiophene units. The introduction of the comonomer can strongly modify the excitonic properties as well as the efficiency of charge-and energy-transfer processes. The choice of the comonomer is thus critical in targeting specific optical properties while maintaining good transport properties.

Nanographenes with zigzag edges are predicted to manifest non-trivial π-magnetism resulting from the interplay of concurring electronic effects, such as hybridization of localized frontier states and Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenues toward organic spintronics. The magnetic stability in nanographenes is thus far limited by the weak magnetic exchange coupling, which remains below the room temperature thermal energy. Here, we report the synthesis of large rhombus-shaped nanographenes with zigzag periphery on gold and copper surfaces. Single-molecule scanning probe measurements show an emergent magnetic spin singlet ground state with increasing nanographene size. The magnetic exchange coupling in the largest nanographene (C 70 H 22 , containing five benzenoid rings along each edge), determined by inelastic electron tunneling spectroscopy, exceeds 100 meV or 1160 K, which outclasses most inorganic nanomaterials and survives on a metal electrode.Magnetism in solids is usually associated to d-or f-block elements. However, since the isolation of graphene, the field of carbon magnetism has gained increased traction 1 . Though

New materials for OLED applications with low singlet-triplet energy splitting have been recently synthesized in order to allow for the conversion of triplet into singlet excitons (emitting light) via a Thermally Activated Delayed Fluorescence (TADF) process, which involves excited-states with a non-negligible amount of Charge-Transfer (CT).The accurate modeling of these states with Time-Dependent Density Functional Theory (TD-DFT), the most used method so far because of the favorable trade-off between accuracy and computational cost, is however particularly challenging. We carefully address this issue here by considering materials with small (high) singlet-triplet gap acting as emitter (host) in OLEDs, and by comparing the accuracy of TD-DFT and the corresponding Tamm-Dancoff Approximation (TDA), which is found to greatly reduce error bars with respect to experiments thanks to better estimates for the lowest singlet-triplet transition. Finally, we quantitatively correlate the singlet-triplet splitting values with the extent of CT, using for it a simple metric extracted from calculations with double-hybrid functionals, that might be applied in further molecular engineering studies.

In this letter we report the error analysis of 59 exchange-correlation functionals in evaluating the structural parameters of small-and medium-sized organic molecules.From this analysis, recently developed double-hybrids, such as xDH-PBE0, emerge as the most reliable methods, while global-hybrids confirm their robustness in reproducing molecular structures. Notably the M06-L density-functional is the only semilocal method reaching an accuracy comparable to hybrids'. A comparison with errors obtained on energetic databases (including thermochemistry, reaction barriers and interaction energies) indicate that most of the functionals have a coherent behavior, showing low (or high) deviations on both energy and structure datasets. Only a few of them are more prone toward one of these two properties. 2The quality of any method rooted in density functional theory (DFT) is (strongly) affected by the choice of the exchange-correlation functional (ECF), which gives the unknown term of the Kohn-Sham energy. If from one side the spreading of DFT in chemistry and physics has encouraged the research of new and better-performing density-functionals, 1 from the other side their validation has become a due step before any routine application. Such a benchmark passes through a careful evaluation (and consequent statistical analysis) of the errors on defined properties and systems sets.Starting from the nineties, a large effort has been made in order to define standard benchmark sets allowing for a meaningful and fair comparison between different ECFs. 2-8Among the properties firstly targeted, atomization energies, ionization potentials and electron affinities 2-4 as well as bond lengths and angles of (mostly) small organic systems received a particular attention. Figure S1 and S2 in the Supporting Information). Both databases are an excellent diagnostic test to discriminate density-functionals in modeling structural parameters of organic systems.In this Letter, we use these two datasets to thoroughly benchmark the accuracy of 59ECFs (reported in Table The references and further details of all the considered computational methods involved in this Letter are given in Table S1 of the Supporting Information.In order to discriminate the accuracy of the selected approaches, we define a criterion based on the matrix containing all the interatomic distances. For each system, we compute the mean absolute deviation (MAD) over the distance matrix of the probed and the reference geometries, and calculate the averaged deviation over the set. Figure 1 reports these statistics for the 63 computational approaches considered in this Letter (see Table S2 and S3 in the Supporting Information for more details).For the CCse21 dataset, the deviations span from 0.002 to 0.016 Å for xDH-PBE0and HF methods, respectively. Within this interval, a smooth transition from high to low accuracy is observed. Apart from the worst performing ECFs like BLYP, B97D, B97D3 or TPSS, most of the methods give a slight increase of the distance matrix deviation (...

On the basis of our previous developments in the field of nonempirical double hybrids, we present here a new exchange-correlation functional based on a range-separated model for the exchange part and integrating a nonlocal perturbative correction to the electron correlation contribution. Named RSX-QIDH, the functional is free from any kind of empirical parametrization. Its range-separation parameter is set to recover the total energy of the hydrogen atom, thus eliminating the self-interaction error for this one-electron system. Subsequent tests on some relevant benchmark data sets confirm that the self-interaction error is particularly low for RSX-QIDH. This new functional provides also correct dissociation profiles for charged rare-gas dimers and very accurate ionization potentials directly from Kohn-Sham orbital energies. Above all, these good results are not obtained at the expense of other properties. Indeed, further tests on standard benchmarks show that RSX-QIDH is competitive with the more empirical ωB97X-2 double hybrid and outperforms the parent LC-PBE long-range corrected hybrid, thus underlining the important role of the nonlocal perturbative correlation.