The role of X-H bonds (X = C, N and O) in internal conversion processes: dibenzoterrylene as an example.

We have developed a theoretical framework for calculating rate constants of internal conversion () in the Franck-Condon (FC) and Herzberg-Teller (HT) approximations. The method accounts for anharmonic vibrational contributions and the Duschinsky effect. Our approach employs recursive dynamic programming to sum over multiple vibrational quantum number combinations and uses a Lagrange-multiplier technique with dispersion broadening to improve the accuracy of the calculated rate constants.

Hyperuniform Mesoporous Gold Films Coated with Halogen-Bonding Metal-Organic Frameworks for Selective Raman Sensing of Chlorinated Hydrocarbons.

The selective detection of chlorinated aromatic hydrocarbons (CAHs) in environmental samples is challenging due to matrix interference effects. We report a surface-enhanced Raman spectroscopy (SERS) sensor that combines mesoporous Au films with UiO-66-I metal-organic framework (MOF) coatings to achieve the selective detection of CAHs. We show that mesoporous Au films can be considered hyperuniform two-dimensional (2D) materials where long-range correlations and local disorder assist in electromagnetic hotspot formation for SERS.

Photolysis of labile bonds towards radical generation: case study of alkyl verdazyls.

Two series of stable verdazyl radical derivatives, specifically 1,2,4,6-substituted-1,4-dihydro-1,2,4,5-tetrazin-3(2)-ones (also called "alkylverdazyls" or "AlkVZs"), were systematically investigated in photoactivated C-N bond homolysis. In-depth evaluation of their mechanisms indicated that several factors played a pivotal role in the generation of radicals during photon absorbance. From quantum chemical calculations, it was found that the most influential factor is the generation of charge-separated excited states, where one electron is located at the verdazyl moiety and the second one is distributed at the alkyl part.

Predicting intersystem crossing rate constants of alkoxy-radical pairs with structure-based descriptors and machine learning.

Peroxy radicals (RO) are ubiquitous intermediates in many oxidation processes, especially in the atmospheric gas phase. The recombination reaction of two peroxy radicals (RO + R'O) has been demonstrated to lead, several steps, to a triplet complex of two alkoxy radicals: (RO˙⋯R'O˙). The different product channels of RO + R'O reactions thus correspond to different reactions of this triplet complex.

Orbital contributions to magnetically induced current densities using gauge-including atomic orbitals.

We have developed a method to calculate orbital contributions to magnetically induced current density (MICD) susceptibilities in molecules using gauge-including atomic orbitals (GIAO). The methods implemented in the GIMIC program have been used for analyzing orbital contributions to magnetically induced ring-current (MIRC) strengths. We have studied five aromatic, one nonaromatic, and four antiaromatic molecules.

Wavelength-dependent intersystem crossing dynamics of phenolic carbonyls in wildfire emissions.

Quantum chemical calculations were employed to construct Jablonski diagrams for a series of phenolic carbonyls, including vanillin, iso-vanillin, 4-hydroxybenzaldehyde, syringaldehyde, and coniferyl aldehyde. These molecules can enter the Earth's atmosphere from forest fire emissions and participate in photochemical reactions within the atmospheric condensed phase, including cloud and fog droplets and aqueous aerosol particles. This photochemistry alters the composition of light-absorbing organic content, or brown carbon, in droplets and particles through the formation and destruction of key chromophores.

Nonradiative Deactivation of the Fluorescent Ag-DNA and Ag-DNA Emitters: The Role of Water.

The luminescent quantum yield of silver-cluster emitters stabilized by short oligonucleotides (Ag-DNA) may be efficiently tuned by replacing nucleobases in their stabilization DNA matrices with analogues. In the present study, we proposed a valuable and straightforward theoretical methodology for assessing the photophysical behaviors emerging in Ag-DNA emitters after excitation. Using green Ag-DNA and near-IR Ag-DNA emitters we demonstrate how point guanine/inosine replacement could affect the photophysical rate constants of radiative/nonradiative processes.

Molecular phosphorescence enhancement by the plasmon field of metal nanoparticles.

A theoretical model is proposed that allows the estimation of the quantum yield of phosphorescence of dye molecules in the vicinity of plasmonic nanoparticles. For this purpose, the rate constants of the radiative and nonradiative intramolecular transitions for rhodamine 123 (Rh123) and brominated rhodamine (Rh123-2Br) dyes have been calculated. The plasmon effect of Ag nanoparticles on various types of luminescence processes has been studied both theoretically and experimentally.

Experimental and computational studies of the optical properties of 2,5,8-tris(phenylthiolato)heptazine with an inverted singlet-triplet gap.

Photophysical properties of the three-fold symmetric 2,5,8-tris(phenylthiolato)heptazine molecule (1) are studied from combined experimental and computational viewpoints. The intense blue photoemission of 1 in the solid state and in toluene solution is proposed to have a fluorescent origin on the basis of a relatively short emission lifetime and no detectable triplet decay. Calculations at correlated levels of theory also show that 1 has a large inverted singlet-triplet (IST) gap, a non-vanishing spin-orbit coupling matrix element between the first excited singlet and triplet states, and a fast intersystem crossing rate constant that leads to singlet population from the higher-lying triplet state.

Engineering Tunable Ratiometric Dual Emission in Single Emitter-based Amorphous Systems.

Molecular emitters with multi-emissive properties are in high demand in numerous fields, while these properties basically depend on specific molecular conformation and packing. For amorphous systems, special molecular arrangement is unnecessary, but it remains challenging to achieve such luminescent behaviors. Herein, we present a general strategy that takes advantage of molecular rigidity and S -T energy gap balance for emitter design, which enables fluorescence-phosphorescence dual-emission properties in various solid forms, whether crystalline or amorphous.

Highly Efficient Room-Temperature Light-Induced Synthesis of Polymer Dots: A Programming Control Paradigm of Polymer Nanostructurization from Single-Component Precursor.

Polymer dots (PDs) have raised considerable research interest due to their advantages of designable nanostructures, high biocompatibility, versatile photoluminescent properties, and recyclability as nanophase. However, there remains a lack of , real-time, and noncontact methods for synthesizing PDs. Here we report a rational strategy to synthesize PDs through a well-designed single-component precursor (an asymmetrical donor-acceptor-donor' molecular structure) by photoirradiation at ambient temperature.

Influence of plasmons on the luminescence properties of solvatochromic merocyanine dyes with different solvatochromism.

The effect of localized surface plasmon resonance (LSPR) of a system consisting of a highly dipolar merocyanine dye and a silver nanoparticle (NP) was studied experimentally and theoretically. A theoretical model for estimating the fluorescence quantum yield () using quantum chemical calculations of intramolecular and intermolecular electronic transition rate constants was developed. Calculations show that the main deactivation channels of the lowest excited singlet state of the studied merocyanines are internal conversion ((S → S)) and fluorescence ((S → S)).

Incorporation of a Fluorine Atom in a Bridging Ligand of Half-Lantern Pt Complexes Provides up to 10-Fold Enhancement of Electroluminescence Brightness.

The binuclear half-lantern platinum(II) complexes [Pt(pbt)(μ-SN)] (pbtH = 2-phenylbenzothiazole, SN = benzo[]thiazole-2-thiolate , 6-fluorobenzo[]thiazole-2-thiolate , 6-chlorobenzo[]thiazole-2-thiolate , 6-bromobenzo[]thiazole-2-thiolate , and 6-iodobenzo[]thiazole-2-thiolate ) were synthesized by the treatment of the in situ formed [Pt(pbt)(NCMe)]NO complex and appropriate benzo[]thiazole-2-thiole in the presence of BuOK; yield: 51-84%. Complexes - exhibit intense red photoluminescence originated from MMLCT state reaching 22% room temperature quantum yields in a CHCl solution. All complexes display excited-state decay kinetics both in solution and in the solid state; the kinetics was adequately modeled by single exponentials.

Gold(i)-containing light-emitting molecules with an inverted singlet-triplet gap.

Delayed fluorescence from molecules with an inverted singlet-triplet gap (DFIST) is the consequence of the unusual reverse order of the lowest excited singlet (S) and triplet (T) states of thermally activated delayed fluorescence (TADF) emitters. Heptazine (1,3,4,6,7,9,9-heptaazaphenalene) derivatives have an inverted singlet-triplet gap thanks to the combination of multiple resonance (MR) effects and a significant double excitation character. Here, we study computationally the effect of gold(i) metalation and coordination on the optical properties of heptazine (molecule 4) and the phosphine-functionalized 2,5,8-tris(dimethylphosphino)heptazine derivatives (molecules 1-3).

Large Gas-Phase Source of Esters and Other Accretion Products in the Atmosphere.

Dimeric accretion products have been observed both in atmospheric aerosol particles and in the gas phase. With their low volatilities, they are key contributors to the formation of new aerosol particles, acting as seeds for more volatile organic vapors to partition onto. Many particle-phase accretion products have been identified as esters.

Computational Investigation of Substituent Effects on the Alcohol + Carbonyl Channel of Peroxy Radical Self- and Cross-Reactions.

Organic peroxy radicals (RO) are key intermediates in atmospheric chemistry and can undergo a large variety of both uni- and bimolecular reactions. One of the least understood reaction classes of RO are their self- and cross-reactions: RO + R'O. In our previous work, we have investigated how RO + R'O reactions can lead to the formation of ROOR' accretion products through intersystem crossings and subsequent recombination of a triplet intermediate complex (RO···OR').

On the origin of the inverted singlet-triplet gap of the 5th generation light-emitting molecules.

Excitation energies of the lowest singlet and triplet state of molecules whose first excited singlet state lies energetically below the first triplet state have been studied computationally at (time-dependent) density functional theory, coupled-cluster, and second-order multiconfiguration perturbation theory levels. The calculations at the levels show that the singlet-triplet gap is inverted as compared to the one expected from Hund's rule, whereas all density functionals yield the triplet state as the lowest excited state. Double excitations responsible for the inverted singlet-triplet gap have been identified.

Photo- and Electroluminescent Neutral Iridium(III) Complexes Bearing Imidoylamidinate Ligands.

Imidoylamidinate-based heteroleptic bis(2-phenylbenzothiazole)iridium(III) and -rhodium(III) complexes [()M(NN)] ( = 2-phenylbenzothiazole, NN = '-(benzo[]thiazol-2-yl)acetimidamidyl ( and ), '-(6-fluorobenzo[]thiazol-2-yl)acetimidamidyl (), '-(benzo[]oxazol-2-yl)acetimidamidyl (), '-(1-methyl-1-benzo[]imidazol-2-yl)acetimidamidyl (); yields 70-84%) were obtained by the reaction of the in situ-generated solvento-complex [()M(NCMe)]NO and benzo[]thia/oxa/-methylimidozol-2-amines in the presence of NaOMe. Complexes - exhibited intense orange photoluminescence, reaching 37% at room temperature quantum yields, being immobilized in a poly(methyl methacrylate) matrix. A photophysical study of these species in a CHCl solution, neat powder, and frozen (77 K) MeOCHOH-EtOH glass matrix─along with density-functional theory (DFT), ab initio methods, and spin-orbit coupling time-dependent DFT calculations─verified the effects of substitution in the imidoylamidinate ligands on the excited-state properties.

Odd-Number Cyclo[]Carbons Sustaining Alternating Aromaticity.

Cyclo[]carbons ( = 5, 7, 9, ...

Non-intersecting ring currents in [12]infinitene.

The aromaticity of the newly synthesized [12]infinitene is addressed via analysis of the magnetically induced current density and the induced magnetic field. Our calculations reveal that [12]infinitene responds to an external magnetic field by creating two current-density pathways that flow diatropically along the edges of the molecule. The current-density pathways do not intersect.

Magnetically induced ring currents in metallocenothiaporphyrins.

The magnetically induced current-density susceptibility tensor (CDT) of the lowest singlet and triplet states of the metallocenothiaporphyrins, where the metal is V, Cr, Mn, Fe, Co, Ni, Mo, Tc, Ru, or Rh, have been studied with the gauge-including magnetically induced currents (GIMIC) method. The compounds containing V, Mn, Co, Tc or Rh were studied as cations because the neutral molecules have an odd number of electrons. The calculations show that the aromatic nature of most of the studied molecules follows the Hückel and Baird rules of aromaticity.

Integration of global ring currents using the Ampère-Maxwell law.

Magnetically induced ring currents are calculated from the magnetic shielding tensor by employing the Ampère-Maxwell law. The feasibility of the method is demonstrated by integrating the component of the shielding tensor along the symmetry axis of highly symmetric ring-shaped aromatic, antiaromatic and nonaromatic molecules. The calculated ring-current strengths agree perfectly with the ones obtained by integrating the current-density flux passing through a plane cutting half the molecular ring.

Computational Investigation of the Formation of Peroxide (ROOR) Accretion Products in the OH- and NO-Initiated Oxidation of α-Pinene.

The formation of accretion products ("dimers") from recombination reactions of peroxyl radicals (RO) is a key step in the gas-phase generation of low-volatility vapors, leading to atmospheric aerosol particles. We have recently demonstrated that this recombination reaction very likely proceeds via an intermediate complex of two alkoxy radicals (RO···OR') and that the accretion product pathway involves an intersystem crossing (ISC) of this complex from the triplet to the singlet surface. However, ISC rates have hitherto not been computed for large and chemically complex RO···OR' systems actually relevant to atmospheric aerosol formation.

Dianthracenylazatrioxa[8]circulene: Synthesis, Characterization and Application in OLEDs.

A soluble, green-blue fluorescent, π-extended azatrioxa[8]circulene was synthesized by oxidative condensation of a 3,6-dihydroxycarbazole and 1,4-anthraquinone by using benzofuran scaffolding. This is the first circulene to incorporate anthracene within its carbon framework. Solvent-dependent fluorescence and bright green electroluminescence accompanied by excimer emission are the key optical properties of this material.

Single-layer polymeric tetraoxa[8]circulene modified by s-block metals: toward stable spin qubits and novel superconductors.

Tunable electronic properties of low-dimensional materials have been the object of extensive research, as such properties are highly desirable in order to provide flexibility in the design and optimization of functional devices. In this study, we account for the fact that such properties can be tuned by embedding diverse metal atoms and theoretically study a series of new organometallic porous sheets based on two-dimensional tetraoxa[8]circulene (TOC) polymers doped with alkali or alkaline-earth metals. The results reveal that the metal-decorated sheets change their electronic structure from semiconducting to metallic behaviour due to n-doping.