Acene-Linked Zethrenes and Bisphenalenyls: A DFT Search for Organic Tetraradicals

Abstract

Polycyclic aromatic hydrocarbons are of special interest due to their promising nonlinear optical and magnetic properties. A series of acene-linked zethrenes and bisphenalenyls comprising from five to nine benzene rings in the linker group have been computationally studied by the DFT UB3LYP/6-311++G­(d,p) quantum-chemical modeling of their electronic structure, possible spin states, and exchange interactions. The zethrenes with octacene and nonacene linkers as well as bisphenalenyls comprising heptacene, octacene, and nonacene linker groups have been revealed to possess tetraradicaloid nature, which makes them promising building blocks for organic optoelectronic and spintronic devices. The results obtained open a way of constructing tetraradicaloid organic molecules characterized by the presence of two types of paramagnetic centers.

Engineering Triangulene Building Blocks with Tunable Magnetic Exchange Coupling for All-Carbon-Based Molecular Spintronics

“…In an attempt to extend the range of the exchange energies, we design the "double-arrow systems", denoted as [n] x,y -arrow, to modulate the interaction between two [n]-TG terminals by inserting a rectangular NG bridge 43,44 with its armchair edge length and zigzag edge width involving x and y hexagons, respectively, e.g., [4] 2,3 -arrow as shown in Scheme 2b. 45,46 For all double-arrow systems considered in this study, a spin-polarized BS ground state is observed. The relative energies for the low-lying spin states of the double-arrow systems with various terminal and bridge sizes are presented in Table S3.…”

Quinonoid versus Aromatic π-Conjugated Oligomers and Polymers and Their Diradical Characters

“…A different class of conjugated polymers with alternating donor–acceptor units show below 1 eV gaps with strong diradical characteristics . The diradical character can be correlated to singlet fission reactions, , electronic properties of an open-shell system such as two photon absorptions, , excitation energies and singlet-triplet energy gaps, , and the optical properties such as hyperpolarizability − and magnetic properties. , A neutral molecule with two unpaired electrons, with strong localization, results in diradicals as illustrated in Figure . Among the various mechanisms of diradical state stabilization, oligomers in this article achieve their singlet diradical character due to the repulsion of electrons with α and β spins.…”

Environmental effects on the singlet fission phenomenon: a model Hamiltonian-based study

“…23–29 Irrespective of the level of theory, wave function-based theory or density functional theory (WFT and DFT, respectively) calculations, such an approximation is considered to be satisfactory for molecular crystals and more questionable in covalent dimers. 30–34…”

“…[23][24][25][26][27][28][29] Irrespective of the level of theory, wave function-based theory or density functional theory (WFT and DFT, respectively) calculations, such an approximation is considered to be satisfactory for molecular crystals and more questionable in covalent dimers. [30][31][32][33][34] However, one may wonder how much the immediate environment of a given monomer may modulate its spectroscopy. In the design of singlet fission compounds, we felt that attention should be paid to the molecular description, and to go beyond the free monomer description.…”