Proton transfer induced excited-state aromaticity gain for chromophores with maximal Stokes shifts.

Excited state aromaticity (ESA) offers a fascinating route for driving photophysical and photochemical processes but is challenging to harness fully due to its inherent association with unstable antiaromatic ground states. Here, we propose to circumvent this problem the introduction of a new class of photophysical processes, the generation of ESA an excited-state intramolecular proton transfer. We select twelve candidate molecules based on the cyclobutadiene and pentalene scaffolds and investigate their ground and excited state properties using computation.

Classification and quantitative characterisation of the excited states of π-conjugated diradicals.

Diradicals are of high current interest as emerging materials for next generation optoelectronic applications. To tune their excited-state properties it would be greatly beneficial to have a detailed understanding of the wave functions of the different states involved but this endeavour is hampered by formal and practical barriers. To tackle these challenges, we present a formal analysis as well as concrete results on diradical excited states.

Near-infrared luminescent open-shell π-conjugated systems with a bright lowest-energy zwitterionic singlet excited state.

Open-shell systems with extensive π-conjugation have fascinating properties due to their narrow bandgaps and spin interactions. In this work, we report neutral open-shell di- and polyradical conjugated materials exhibiting intriguing optical and magnetic properties. Our key design advance is the planarized geometry allowing for greater interaction between adjacent spins.

Singlet Fission in Pechmann Dyes: Planar Chromophore Design and Understanding.

Singlet fission in organic chromophores holds the potential for enhancing photovoltaic efficiencies beyond the single-junction limit. The most basic requirement of a singlet fission material is that it has a large energy gap between its first singlet and triplet excited states. Identifying such compounds is not simple and has been accomplished either through computational screening or by subtle modifications of previously known fission materials.

Suppression of Dexter transfer by covalent encapsulation for efficient matrix-free narrowband deep blue hyperfluorescent OLEDs.

Hyperfluorescence shows great promise for the next generation of commercially feasible blue organic light-emitting diodes, for which eliminating the Dexter transfer to terminal emitter triplet states is key to efficiency and stability. Current devices rely on high-gap matrices to prevent Dexter transfer, which unfortunately leads to overly complex devices from a fabrication standpoint. Here we introduce a molecular design where ultranarrowband blue emitters are covalently encapsulated by insulating alkylene straps.

Reducing undesired solubility of squarephaneic tetraimide for use as an organic battery electrode material.

Locally aromatic alkyl--substituted squarephaneic tetraimide (SqTI) conjugated macrocycles are four-electron reducible, owing to global aromaticity and presumed global Baird aromaticity of the dianion and tetraanion states, respectively. However, their good solubility inhibits their application as a battery electrode material. By applying sidechain removal as a strategy to reduce SqTI solubility, we report the development of its unsubstituted derivative SqTI-H, which was obtained directly from squarephaneic tetraanhydride by facile treatment with hexamethyldisilazane and MeOH.

Quantification of the Ionic Character of Multiconfigurational Wave Functions: The Diagnostic.

The complete active space self-consistent field (CASSCF) method is a cornerstone in modern excited-state quantum chemistry providing the starting point for most common multireference computations. However, CASSCF, when used with a minimal active space, can produce significant errors (>2 eV) even for the excitation energies of simple hydrocarbons if the states of interest possess ionic character. After illustrating this problem in some detail, we present a diagnostic for ionic character, denoted as  , that is readily computed from the transition density.

Functionalisation of conjugated macrocycles with type I and II concealed antiaromaticity cross-coupling reactions.

Conjugated macrocycles can exhibit concealed antiaromaticity; that is, despite not being antiaromatic, under specific circumstances, they can display properties typically observed in antiaromatic molecules due to their formal macrocyclic 4 π-electron system. Paracyclophanetetraene (PCT) and its derivatives are prime examples of macrocycles exhibiting this behaviour. In redox reactions and upon photoexcitation, they have been shown to behave like antiaromatic molecules (requiring type I and II concealed antiaromaticity, respectively), with such phenomena showing potential for use in battery electrode materials and other electronic applications.

The OpenMolcas : A Community-Driven Approach to Advancing Computational Chemistry.

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations.

Expedient synthesis and luminescence sensing of the inositol pyrophosphate cellular messenger 5-PP-InsP.

Inositol pyrophosphates are important biomolecules associated with apoptosis, cell growth and kinase regulation, yet their exact biological roles are still emerging and probes do not exist for their selective detection. We report the first molecular probe for the selective and sensitive detection of the most abundant cellular inositol pyrophosphate 5-PP-InsP, as well as an efficient new synthesis. The probe is based on a macrocyclic Eu(iii) complex bearing two quinoline arms providing a free coordination site at the Eu(iii) metal centre.

Classification of doubly excited molecular electronic states.

Electronic states with partial or complete doubly excited character play a crucial role in many areas, such as singlet fission and non-linear optical spectroscopy. Although doubly excited states have been studied in polyenes and related systems for many years, the assignment as singly doubly excited, even in the simplest case of butadiene, has sparked controversies. So far, no well-defined framework for classifying doubly excited states has been developed, and even more, there is not even a well-accepted definition of doubly excited character as such.

Energy Component Analysis for Electronically Excited States of Molecules: Why the Lowest Excited State Is Not Always the HOMO/LUMO Transition.

The ability to tune excited-state energies is crucial to many areas of molecular design. In many cases, this is done based on the energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). However, this viewpoint is incomplete neglecting the many-body nature of the underlying excited-state wave functions.

Squarephaneic Tetraanhydride: A Conjugated Square-Shaped Cyclophane for the Synthesis of Porous Organic Materials.

Aromatic carboxylic anhydrides are ubiquitous building blocks in organic materials chemistry and have received considerable attention in the synthesis of organic semiconductors, pigments, and battery electrode materials. Here we extend the family of aromatic carboxylic anhydrides with a unique new member, a conjugated cyclophane with four anhydride groups. The cyclophane is obtained in a three-step synthesis and can be functionalised efficiently, as shown by the conversion into tetraimides and an octacarboxylate.

Non-Kasha fluorescence of pyrene emerges from a dynamic equilibrium between excited states.

Pyrene fluorescence after a high-energy electronic excitation exhibits a prominent band shoulder not present after excitation at low energies. The standard assignment of this shoulder as a non-Kasha emission from the second-excited state (S) has been recently questioned. To elucidate this issue, we simulated the fluorescence of pyrene using two different theoretical approaches based on vertical convolution and nonadiabatic dynamics with nuclear ensembles.

Newton-X Platform: New Software Developments for Surface Hopping and Nuclear Ensembles.

Newton-X is an open-source computational platform to perform nonadiabatic molecular dynamics based on surface hopping and spectrum simulations using the nuclear ensemble approach. Both are among the most common methodologies in computational chemistry for photophysical and photochemical investigations. This paper describes the main features of these methods and how they are implemented in Newton-X.

Squarephaneic Tetraanhydride: A Conjugated Square-Shaped Cyclophane for the Synthesis of Porous Organic Materials.

Aromatic carboxylic anhydrides are ubiquitous building blocks in organic materials chemistry and have received considerable attention in the synthesis of organic semiconductors, pigments, and battery electrode materials. Here we extend the family of aromatic carboxylic anhydrides with a unique new member, a conjugated cyclophane with four anhydride groups. The cyclophane is obtained in a three-step synthesis and can be functionalised efficiently, as shown by the conversion into tetraimides and an octacarboxylate.

Using diketopyrrolopyrroles to stabilize double excitation and control internal conversion.

Diketopyrrolopyrrole (DPP) is a pivotal functional group to tune the physicochemical properties of novel organic photoelectronic materials. Among multiple uses, DPP-thiophene derivatives forming a dimer through a vinyl linker were recently shown to quench the fluorescence observed in their isolated monomers. Here, we explain this fluorescence quenching using computational chemistry.

Hierarchical Assembly of a Micro- and Macroporous Hydrogen-Bonded Organic Framework with Tailored Single-Crystal Size.

Porous organic molecular materials represent an emergent field of research in Chemistry and Materials Science due to their unique combination of properties. To enhance their performance and expand the number of applications, the incorporation of hierarchical porosity is required, as exclusive microporosity entails several limitations. However, the integration of macropores in porous organic molecular materials is still an outstanding challenge.

Reversible P-P bond cleavage at an iridium(III) metal centre.

Treatment of a κ-P-monodentate bicyclic diphosphane iridium(III) complex with a labile gold(I) precursor afforded an unusual Ir/Au complex in which the P-P single bond has been cleaved. This reaction was cleanly reversed upon addition of tertiary phosphine. Carbon-carbon bond activation, across neighbouring PCN rings of the coordinated bicyclic diphosphane, occurred upon thermolysis of the Ir/Au complex.

Sterically demanding macrocyclic Eu(iii) complexes for selective recognition of phosphate and real-time monitoring of enzymatically generated adenosine monophosphate.

The design of molecular receptors that bind and sense anions in biologically relevant aqueous solutions is a key challenge in supramolecular chemistry. The recognition of inorganic phosphate is particularly challenging because of its high hydration energy and pH dependent speciation. Adenosine monophosphate (AMP) represents a valuable but elusive target for supramolecular detection because of its structural similarity to the more negatively charged anions, ATP and ADP.