On-Surface Synthesis and Characterization of a High-Spin Aza-[5]-Triangulene.

Triangulenes are a class of open-shell triangular graphene flakes with total spin increasing with their size. In the last years, on-surface-synthesis strategies have permitted fabricating and engineering triangulenes of various sizes and structures with atomic precision. However, direct proof of the increasing total spin with their size remains elusive.

Near-Unity Triplet Generation Promoted via Spiro-Conjugation.

An intersystem crossing (ISC) rate constant of 1.0×10  s was previously registered with a spiro-bis-benzophenone scaffold. Triplet generation efficiency could be further enhanced by stabilizing the spiro-charge-transfer (CT) state and rationally designing spiro-compounds (SCTs) that consist of electron-rich diphenyl ether as the spiro-CT donor and electron-deficient dinaphthyl ketone as the spiro-CT acceptor.

Engineering the Charge-Transfer State to Facilitate Spin-Orbit Charge Transfer Intersystem Crossing in Spirobis[anthracene]diones.

Spiro conjugation has been proposed to dictate the efficiency of charge transfer, which could directly affect the spin-orbit charge transfer intersystem crossing (SOCT-ISC) process. However, this process has yet to be exemplified. Herein, we prepared three spirobis[anthracene]diones, in which two benzophenone moieties are locked in close proximity and differentially functionalized to fine-tune the charge transfer state.

Singlet fission in spiroconjugated dimers.

Spiroconjugation results in a unique arrangement of conjugated fragments providing a novel way to chemically connect chromophoric units and control their electronic interaction, which is a key factor for the viability of the singlet fission photophysical reaction. In this study, we computationally explore the possibility of intramolecular singlet fission in spiroconjugated dimers by characterizing the nature of the low-lying excited electronic states, evaluating the magnitude of interstate couplings, describing possible singlet fission mechanisms, and investigating the potential role of low and high frequency vibrational modes in the exciton fission process. The spiro linkage of organic chromophores with the proper excited singlet and triplet energies favors the presence of low-lying charge resonance states, which play a major role in the formation of the triplet pair state.

Triangular graphene nanofragments: open-shell character and doping.

In this work we study the intricacies of the electronic structure properties of triangular graphene nanofragments (TGNFs) in their ground and low-lying excited states by means of ab initio quantum chemistry calculations. We focus our attention on the radical and diradical characters of phenalenyl and triangulene, the smallest members of the TGNF family, and we describe the nature of their low-lying excited states. Moreover, we rationalize the modulation of the electronic and magnetic properties by means of selective boron or nitrogen substitution of carbon sites and by hydrogen saturation.

Thieno[3,4-c]pyrrole-4,6-dione Oligothiophenes Have Two Crossed Paths for Electron Delocalization.

A new series of electron-deficient oligothiophenes, thieno[3,4-c]pyrrole-4,6-dione oligothiophenes (OTPD ), from the monomer to hexamer, is reported. The optical and structural properties in the neutral states have been analyzed by absorption and emission spectroscopy together with vibrational Raman spectroscopy. In their reduced forms, these molecules could stabilize both anions and dianions in similar ways.

Stable 2D anti-ferromagnetically coupled fluorenyl radical dendrons.

We report the first class of stable, two-dimensional (2D) anti-ferromagnetically coupled dendritic polyradicaloids. A kinetically blocked fluorenyl radical was used to build up the first and second generation dendrons and containing three and seven fluorenyl units, respectively. The neighboring fluorenyl radicals in and show moderate anti-ferromagnetic exchange interaction, resulting in a doublet and quartet ground state, respectively, with a small doublet-quartet energy gap.

Isomerism, Diradical Signature, and Raman Spectroscopy: Underlying Connections in Diamino Oligophenyl Dications.

A diradical dication of a 4,4'-di(bis(1,4-methylphenyl)amino)-p-terphenyl oligomer has been characterized in solid-state by Raman spectroscopy and thermo-spectroscopy together with quantum chemical calculations. The diradical character has been evaluated on the basis of the Raman spectra and as a function of temperature. A complete understanding of the nature of the changes in solid state has been provided based on a pseudo-Jahn-Teller effect, which is feasible owing to the fine balance between quinoidal/aromatic extension among consecutive rings and steric crowding.

Fluorenyl Based Macrocyclic Polyradicaloids.

Synthesis of stable open-shell polyradicaloids including control of intramolecular spin-spin interactions is a challenging topic in organic chemistry and materials science. Herein, we report the synthesis and physical characterization of two series of fluorenyl based macrocyclic polyradicaloids. In one series (FR-MCn, n = 4-6), the fluorenyl radicals are directly linked at 3,6-positions; whereas in the other series (MC-FnAn, n = 3-5), an additional ethynylene moiety is inserted between the neighboring fluorenyl units.

Low-Lying ππ* States of Heteroaromatic Molecules: A Challenge for Excited State Methods.

The description of low-lying ππ* states of linear acenes by standard electronic structure methods is known to be challenging. Here, we broaden the framework of this problem by considering a set of fused heteroaromatic rings and demonstrate that standard electronic structure methods do not provide a balanced description of the two (typically) lowest singlet state (La and Lb) excitations. While the Lb state is highly sensitive to correlation effects, La suffers from the same drawbacks as charge transfer excitations.

In Silico Design of Monomolecular Drug Carriers for the Tyrosine Kinase Inhibitor Drug Imatinib Based on Calix- and Thiacalix[n]arene Host Molecules: A DFT and Molecular Dynamics Study.

The use of functionalized calix- and thia-calix[n]arenes is proposed as the basis for our in silico design of a suitable drug carrier for the tyrosine kinase inhibitor, Imatinib. Their mutual electronic properties and interaction energies, Eint, were assessed with the use of Density Functional Theory (DFT) methods under the NBODel methodology. Three structural variables for the host molecules were considered: R = {SO3H (1), t-Bu (2), i-Pr (3), COOH (4), (CH2)2OH (5), (CH2)2NH2 (6)}; b = {CH2, S}; n = {5, 6, 8}, and two possible orientations for the insertion of Imatinib within the macrocycle cavity: pyridine moiety pointing inward (N1) and piperazine pointing inward (N2).