Synthesis of Liquid Crystalline 4H-Benzo[1,2,4]thiadiazines and Generation of Persistent Radicals

Abstract

Four substituted 4H-benzo[1,2,4]thiadiazines 2 were prepared by condensation of the appropriate anilines and benzonitriles followed by oxidative cyclization. The preparation of three fluorinated derivatives 2b-2d proceeded smoothly, while the synthesis of 2a was problematic, presumably due to the relatively high electron density of the benzene ring. The four-ring derivatives 2c and 2d exhibited liquid crystalline properties (2c: Cr 95 SmA 158 I and 2d: Cr 142 SmA 212 I). 4H-Benzo[1,2,4]thiadiazines 2 were oxidized with AgO to generate the corresponding persistent radicals 1 (g=2.0057). The stability of the radicals followed the order 1b approximately 1d>1c>1a, and the two fluorinated radicals 1b and 1d were isolated as crude solids. The lower stability of 1c is presumably due to the presence of the reactive benzylic CH position, and 1a lacks the stabilizing effect of the three fluorine atoms. ESR spectra for 1 were simulated using DFT-derived hfcc as the starting point.

Synthesis and characterization of green-to-yellow emissive Ir(III) complexes of pyridylbenzothiadiazine ligand

“…The family of benzo[e] [1,2,4]thiadiazine with sulfur in various oxidation states has attracted attention for both materials and pharmaceutical applications [8]. While there are a number of synthetic methodologies to access specific derivatives of fused aryl-1,2,4-thiadiazines depending on the fused substituent [8][9][10], to the best of our knowledge, until now there is only one report of using 3-(pyridin-2-yl)-4H-benzo[e] [1,2,4]thiadiazine (L1) as a bidentate N,N′-chelating ligand, and this with respect to complexation with first row transition metals [11].…”

“…While there are a number of synthetic methodologies to access specific derivatives of fused aryl-1,2,4-thiadiazines depending on the fused substituent [8][9][10], to the best of our knowledge, until now there is only one report of using 3-(pyridin-2-yl)-4H-benzo[e] [1,2,4]thiadiazine (L1) as a bidentate N,N′-chelating ligand, and this with respect to complexation with first row transition metals [11]. We thus became interested to attach L1 to the [Ir(ppy) 2 ] + core and study the structure-property relationship of the resulting complexes.…”

Pushing the Boundaries of Intrinsically Stable Radicals: Inverse Design Using the Thiadiazinyl Radical as a Template

“…Considering the fact that their structures are nearly planar, these radicals seem suitable to construct structural elements of liquid crystals. [19]…”

EPR studies of the dynamics and phase behaviour of dithiadiazolyl radicals derived from mesogenic precursors

“…[7,8] A few attempts have been made to synthesise organic free radical mesogens based on both N/O and N/S free radicals [9,10] and the successful characterisation of the first liquid-crystalline S/N radical by Kaszynski is particularly noteworthy within the context of the current studies. [11] The success of paramagnetic materials as liquid crystals however, tends to be limited by the bulk of the metal ion's coordination sphere or the bulk of groups required to stabilise the N/O-based radical electron sterically. [12] This additional bulk can have an adverse effect on the liquid-crystalline properties due to increased viscosity and a slower switching response.…”