A Solid-State Effect Responsible for an Organic Quintet State at Room Temperature and Ambient Pressure - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Advanced Materials Année : 2015

A Solid-State Effect Responsible for an Organic Quintet State at Room Temperature and Ambient Pressure

Résumé

Organic molecules with a higher spin state such as quintet ground state have been observed at low temperatures but they could not exist at higher temperature due to chemical instability. [ 10 ] However, Kekulé diradicals are expected to provide the necessary stability. [ 2 ] Organic stable radicals have been studied extensively for decades. [ 1b ] Among them, 1,3-diaryl-1,2,4-benzotriazinyl radicals have attracted our attention due to their interesting magnetic, as well as electronic properties, and more importantly , their exceptional air and moisture stability. [ 11 ] In the past, we have been interested in linking two of the 1,3-diaryl-1,2,4-benzo triazinyl radical moieties in a single molecule. We designed a hexa-azaanthracene with the goal of generating a stable triplet molecule as shown in 1T (Figure 1), based on the notion that the aromatic sextet would dominate the stability of the molecule and that the two unpaired spins would not be able to pair due to their location relative to each other (1,3-aromatic substitution). Instead, very surprisingly, 1ZI was formed (Figure 1). In this case cyanine stabilization over aromaticity was the driving force. [ 12 ] This unexpected result, coupled with the observation that QDM derivatives have, in some cases, produced diradical contributions to the overall structure (diradicaloids), [ 2,8 ] led us to design 6,6-bis(2-ethylhexyl)-1,1′,3,3′-tetraphenyl-4,6-dihydro-1H-fl uoreno[2,3,8,9]-1,2,4-ditriazin-4-yl (FDT). Here, we demonstrate the fi rst example of synthesis and characterization of an organic diradicaloid based on stable benzotri-azinyls. We further show that electron spin resonance (ESR) spectra of a polycrystalline sample of FDT resulted in the discovery of a, so far unprecedented, intermolecular quintet state at room temperature, supported by the following observations: i) recording of the Δ M s = ±2 forbidden transition by ESR spectros-copy; ii) essentially perfectly superimposable simulation of the ESR spectrum for a quintet and NOT for a triplet; and iii) density functional theory calculations. Variable-temperature (VT) NMR, bond-length analyses, and DFT calculations indicated that the molecule has contributions from a closed shell, covalent structure (FDT (QI)) and an open shell diradical canonical form (FDT) (Figure 1). Static magnetic susceptibility studies showed that the effective magnetic moment continuously decreased with decreasing temperature, and surprisingly, increasing magnetic fi eld strength. A paramagnetic susceptibility was observable only at very weak fi eld strengths (100–1000 Oe). At higher fi eld strengths, the solid is diamagnetic. The same material can be fabricated into a near-infrared (NIR) photodetector with detectivity over 10 11 cm Hz 1/2 W –1 at 1200 nm. The synthetic route to FDT followed the familiar procedure [ 13 ] for the formation of benzotriazinyls, shown in Obtaining high-spin-state organic solids at ambient conditions has been the goal of organic materials scientists, chemists, and physicists because they would enable, not only a fundamental understanding of the nature of spin–spin correlations , but also provide a wide range of advanced applications, quantum information processing systems, and organic spin-tronics. [ 1 ] Molecules with two unpaired electrons have been heavily investigated in the recent past. [ 2 ] Delocalized diradicals can be divided into Kekulé and non-Kekulé structures. Typical examples of non-Kekulé molecules are meta-quinodimethane (m-QDM), [ 3 ] trimethylenemethanes, [ 4 ] and nitrogen-centered (aminyl) radicals. [ 5 ] Only a few molecules with stable open shell structures at room temperature have been studied, such as a suitably substituted corannulene, [ 6 ] bis(triarylamine) dicat-ions, [ 7 ] p-quinodimethanes [ 8 ] and specifi cally designed poly-cyclic aromatic hydrocarbons. [ 9 ] An essential component of all these molecules is the proper substitution to stabilize the unpaired electrons.

Domaines

Matériaux

Dates et versions

hal-01337313 , version 1 (21-07-2016)

Identifiants

Citer

Yonghao Zheng, Mao-Sheng Miao, Géraldine Dantelle, Nancy D. Eisenmeger, Guang Wu, et al.. A Solid-State Effect Responsible for an Organic Quintet State at Room Temperature and Ambient Pressure. Advanced Materials, 2015, 27 (10), pp.1718-1723. ⟨10.1002/adma.201405093⟩. ⟨hal-01337313⟩

Collections

UGA CNRS NEEL
81 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More