Optical Activity of Spin-Forbidden Electronic Transitions in Metal Complexes from Time-Dependent Density Functional Theory with Spin-Orbit Coupling

The Amsterdam Modeling Suite

In this paper, we present the Amsterdam Modeling Suite (AMS), a comprehensive software platform designed to support advanced molecular and materials simulations across a wide range of chemical and physical systems. AMS integrates cutting-edge quantum chemical methods, including Density Functional Theory (DFT) and time-dependent DFT, with molecular mechanics, fluid thermodynamics, machine learning techniques, and more, to enable multi-scale modeling of complex chemical systems. Its design philosophy allows for seamless coupling between components, facilitating simulations that range from small molecules to complex biomolecular and solid-state systems, making it a versatile tool for tackling interdisciplinary challenges, both in industry and in academia. The suite also emphasizes user accessibility, with an intuitive graphical interface, extensive scripting capabilities, and compatibility with high-performance computing environments.

Bromo-Heptahelicene-Bis-Thiadiazole: Photophysics, Chiroptics, and Excited-State Dynamics

The synthesis of a [7]helicene bromide derivative with two fused 2,1,3-thiadiazole heterocycles (TD[7]Br) and a comprehensive study of its photophysical and chiroptical characteristics are presented along with a comparison with 9-bromo-carbo[7]helicene ([7]Br) and 2,15-dibromo-carbo[6]helicene ([6]Br). The integration of a bromine heavy atom onto the helicene backbone facilitates efficient singlet-to-triplet conversion allowing to investigate the resulting fluorescence and phosphorescence properties. The steady-state chiroptical features of the systems are demonstrated through electronic circular dichroism and circularly polarized luminescence. Interestingly, a fluorescence quantum yield of 14% is obtained, a 17-fold increase compared to the corresponding bromo-heptacarbohelicene, and phosphorescence dissymmetry factors reach ±1.2 × 10-2 at 580 nm at low temperature. Finally, the exploration of various excited states generated during the excitation process and their dynamics is delved into by employing nonpolarized transient absorption and emission spectroscopies, thus, highlighting the fruitful combination of heavy-atom effect and charge transfer. The experimental results are understood through time-dependent density functional theory computations.

Optically active cofacial ABCD-Pt(II)-porphyrin dimer exhibits bright circularly polarized phosphorescence

Synthesis of an intrinsically chiral cofacial ABCD-Pt(II)-porphyrin (Por) dimer was achieved by the simple Pt-templated synthesis of Por, followed by Suzuki-Miyaura cross-coupling. The isolated enantiomers exhibited bright red circularly polarized phosphorescence with a BCPP value above 101 M-1 cm-1.

Tri-n-butyl Phosphate vs Tri-iso-amyl Phosphate Complexation with Th(IV), U(VI), and Nd(III): From Theory to Experiment

The complexation behavior of tri-iso-amyl phosphate (TiAP) and tri-n-butyl phosphate (TBP) ligands with U(VI), Th(IV), and Nd(III) was investigated using density functional theory (DFT). Quantum chemical calculations yielded identical coordination geometries for TBP and TiAP complexes. Calculated complexation energies indicated a preferential extraction of U(VI) followed by Th(IV) over Nd(III), aligning with solvent extraction experiments conducted in the cross-current mode. Notably, during the separation of Th(IV) from RE(III), an increase in Th(IV) loading in the organic phase suppressed RE(III) extraction. Further analysis highlighted the crucial role of structural features (symmetry and dipole moment) in the extraction behavior of complexes. Energy decomposition analysis underscored the essential role of geometric strain and dispersion interaction energies in deciding the stability of the complexes.

Enantiopure [6]-Azairidahelicene by Dynamic Kinetic Resolution of a Configurationally Labile [4]-Helicene

A pair of enantiopure [6]-azairidahelicenes incorporating chirality at the metal center and on the helicenic ligand were synthesized by dynamic kinetic resolution (dkr) of a configurationally labile [4]-helicenic ligand (4-(2-pyridyl)-benzo[g]phenanthrene, L1H) using bis-cyclometalated chiral-at-metal only iridium(III) precursors as chiral inductors. The origin of the observed dkr is attributed to the different conformation and stability of diastereomeric reaction intermediates formed during the cyclometalation process. The isolated enantiomers exhibited circularly polarized phosphorescence (CPP), with |gphos| values of 1.8×10-3.

A Perspective on the Simulation of Electronic Circular Dichroism and Circularly Polarized Luminescence Spectra in Chiral Solid Materials

Chiral materials have shown tremendous potential for many technological applications, such as optoelectronics, sensing, magnetism, information technology, and imaging. Characterization of these materials is mostly based on chiroptical spectroscopies, such as electronic circular dichroism (ECD) and circularly polarized luminescence (CPL). These experimental measurements would greatly benefit from theoretical simulations for interpretation of the spectra as well as predictions on new materials. While ECD and CPL simulations are well established for molecular systems, they are not for materials. In this Perspective, we describe the theoretical quantities necessary to simulate ECD and CPL spectra in oriented systems. Then, we discuss the approximate strategies currently used to perform these calculations, what computational machinery is already available to develop more general approaches, and some of the open challenges for the simulation of ECD and CPL spectra in solid materials. When methods that are as reliable and computationally efficient as those for molecules are developed, these simulations will provide invaluable insight and guidance for the rational design of optically active materials.

Circularly polarized phosphorescence with a large dissymmetry factor from a helical platinum(II) complex

A chiral platinum(II) complex with a helical Schiff-base [4]helicene ligand exhibits intense red circularly polarized phosphorescence (CPP) with a glum of 0.010 in the dilute solution state. The intense CPP was caused by a change in the electronic transition character based on the induction of the helical structure.

Understanding the Complexation Behavior of Carbamoylphosphine Oxide Ligands with Representative f-Block Elements

The complexation behavior of carbamoylmethylphosphine oxide ligands (CMPO), a bifunctional phosphine oxide, and their substituted derivatives with Ce(III), Eu(III), Th(IV), U(VI), and Am(III) was probed at the density functional theory (DFT) level. The enhanced extraction of trivalent rare earth elements by the 2-diphenylphosphinylethyl derivative over the conventional CMPO ligand is identified due to the availability of an additional P═O donor group in the former. In addition, the orbital and dispersive interactions play a vital role in the preference of Th(IV) over U(VI) during extraction using CMPO ligands. The better complexing ability of ligands having long alkyl chain substituents at the P atom is justified due to the observed enhanced dispersion interactions in these systems.

Pivotal role of transition density in circularly polarized luminescence

Realizing high luminescence dissymmetry factor (g) in circularly polarized luminescence (CPL) materials remains a big challenge, which necessitates understanding systematically how their molecular structure controls the CPL. Here we investigate representative organic chiral emitters with different transition density distributions and reveal the pivotal role of transition density in CPL. We rationalize that to obtain large g-factors, two conditions should be simultaneously satisfied: (i) the transition density for the S₁ (or T₁)-to-S₀ emission must be delocalized over the entire chromophore; and (ii) the chromophore inter-segment twisting must be restricted and tuned to an optimal value (∼50°). Our findings offer molecular-level insights into the CPL of organic emitters, with potential applications in the design of chiroptical materials and systems with strong CPL effects.

Enantiopure cycloplatinated pentahelicenic N-heterocyclic carbenic complexes that display long-lived circularly polarized phosphorescence

The preparation of the first enantiopure cycloplatinated complexes bearing a bidentate, helicenic N-heterocyclic carbene and a diketonate ancillary ligand is presented, along with their structural and spectroscopic characterization based on both experimental and computational studies. The systems exhibit long-lived circularly polarized phosphorescence in solution and in doped films at room temperature, and also in a frozen glass at 77 K, with dissymmetry factor g_lum values ≥10^-3 in the former and around 10^-2 in the latter.

Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission

The experimental measurement of the photophysical and chiroptical properties of helicene-based π-conjugated emitters with electron-accepting (-CN, -py, -NO₂) or donating (TMS, NMe₂, NH₂) moieties is reported at low temperature (77 K). The samples exhibit strong circularly polarized phosphorescence in frozen solution of 2-MeTHF, with a luminescence dissymmetry factor reaching 1.6 × 10^-2 and a lifetime of over 0.46 s for the most active molecule, the nitro compound. The theoretical investigation shows that although the singlet (S₁) and triplet (T₁) excited-state emissions mainly arise from the helicene core, the rotatory strengths of the spin-allowed versus spin-forbidden emission have opposite signs. Further analysis of the spin-orbit coupling matrix elements shows that there is no strong mixing between S₁ and T₁, justifying the different signs of the rotatory strengths. In the case of the nitro compound, the enhanced phosphorescence emission is due to an efficient intersystem crossing.