Tandem arrays of TEMPO and nitronyl nitroxide radicals with designed arrangements on DNA.

Herein we describe one-dimensional electron-spin arrays consisting of two different organic radicals with the designed arrangement based on the DNA sequence. Two mismatch-binding ligands carrying 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO) and nitronyl nitroxide selectively bind to the predetermined sites on double stranded DNA. By using the two mismatch-binding ligands carrying the organic radicals as the glue for DNA, electron-spin assembly could be successfully synchronized with the hybridization.

Programmed assembly of organic radicals on DNA.

Nitronyl nitroxide radical introduced to naphthyridine carbamate dimer is noncovalently bound to a CGG/CGG triad as an addressable position in DNA duplexes, leading to the programmed assembly of the radical molecules into an 11-mer duplex and a tandem repetitive array of double stranded DNA.

A guanine-substituted nitronyl nitroxide radical forming a one-dimensional ferromagnetic chain.

A stable guanine-substituted nitronyl nitroxide radical 1 has been synthesized and characterized. The single-crystal structure analyses and magnetic susceptibility measurements exhibit a one-dimensional architecture of guanine base resulting from carbonyl-amino hydrogen bonds in the solid state, giving a 1D ferromagnetic chain of the radical moieties.

Theoretical study on spin alignments in ferromagnetic heterospin chains with competing exchange interactions: a generalized ferrimagnetic system containing organic biradicals in the singlet ground state.

Spin alignments in heterospin chains are examined from numerical calculations of model spin Hamiltonians. The Hamiltonians of the heterospin chains mimic an open-shell molecular assemblage composed of an organic biradical in a singlet (S = 0) ground state and a doublet (S = 1/2) monoradical, which are coupled by intermolecular ferromagnetic exchange interactions. It is found from numerical calculations of the spin Hamiltonians that the spin value S2 of the ground-state singlet biradical embedded in the exchange-coupled assemblage deviates from zero and contributes to the bulk magnetization.

Exchange interaction in covalently bonded biradical-monoradical composite molecules.

As a novel molecular designing for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component ferrimagnetics". When a pi-biradical with an S = 1 ground state and a pi-monoradical with S = (1)/(2) are united by sigma-bonds, the pi-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S = 1 and (1)/(2) in the single molecule, serving as a building block for organic molecule-based ferrimagnets under favorable conditions (single-component ferrimagnetics).

Experimental evidence for the triplet-like spin state appearing in ground-state singlet biradicals as a key feature for generalized ferrimagnetic spin alignment.

The authors have previously proposed a theoretical model for exotic spin alignment in organic molecular assemblages: The alternating chain of organic biradicals in a singlet (Sb=0) ground state and monoradicals with S=1/2 has a ferrimagnetic ground state for the whole chain, which has been termed generalized ferrimagnetism. An important feature of the generalized ferrimagnetic spin alignment has been found in the deviation of the expectation value Sb2 of the biradical spin from zero. Even a triplet-like spin state Sb2=2 (Sb=1) has been predicted in the theoretical calculations.