POLYMORPHISM OF 4,7-DIPHENYL-2,1,3-BENZOTHIADIAZOLE DERIVATIVE CRYSTALS

Postnikov V.A.^(1,2), Sorokin T.A.^(1,2), Yurasik G.A.^(1,2),
Kulishov A.A.^(1,2), Sorokina N.I.⁽¹⁾, Borshchev O.V.⁽²⁾

⁽¹⁾ Shubnikov Institute of Crystallography, Kurchatov Complex of Crystallography
and Photonics, National Research Centre “Kurchatov Institute”

117342, Moscow, Butlerova st., 17a

⁽²⁾ Enikolopov Institute of Synthetic Polymer Materials of RAS

117393, Moscow, Profsoyuznaya st., 70

4,7-Diphenyl-2,1,3-benzothiadiazole (P-BTD) and its derivatives (R-P-BTD) are thermo- and chemically stable luminophores featuring a large Stokes shift and efficient emission in both solutions and crystals. Consequently, they are in demand for a wide range of applications in photonics and electronics [1]. Crystalline materials based on these compounds, both in bulk and thin-film form, are of particular interest. However, according to recent studies, conformational crystal polymorphism is frequently observed in the R-P-BTD family of compounds [1,2], which is of great interest for elucidating structure–property relationships. This work discusses the results of a study on the polymorphism of crystals of R-P-BTD-type compounds bearing trimethylsilyl (TMS-P-BTD) [2] and phenyl (P-P-BTD) terminal substituents (see Figure).

TMS-P-BTD	P-P-BTD
Chemical structural formulas of the compounds studied

Using single-crystal X-ray diffraction, three polymorphic forms were identified for TMS-P-BTD: I – monoclinic (sp. gr. P2₁/c, Z/Zʹ = 32/8), II – orthorhombic Pnaa (sp. gr. Pnaa, Z/Zʹ = 12/1.5) and III – triclinic (sp. gr. P-1, Z/Zʹ = 8/4) [2]. For P-P-BTD, two polymorphic forms were established: α – triclinic (sp. gr. P-1, Z/Zʹ = 2/1; a=10.1065(2), b=10.5274(2), c=10.7378(2) Å; α=91.106(1)°, β=98.363(1)°, γ=103.839(1)°) and β – monoclinic (sp. gr. C2/c, Z/Zʹ = 16/2; a=23.0533(2), b=27.5264(10) c=18.9876(12) Å; β=127.159(1)°). The thermodynamic and kinetic aspects of phase transitions in the studied polymorphic systems are discussed.

1. Echeverri M. et. al. Stimuli-Responsive Benzothiadiazole Derivative as a Dopant for Rewritable Polymer Blends // ACS Appl. Mater. Interfaces. 2020. Vol. 12. P. 10929−10937. https://doi.org/10.1021/acsami.9b21209

2. Postnikov V.A. et. al. Conformational Polymorphism of 4,7-Bis(4-(trimethylsilyl)phenyl)- 2,1,3-benzothiadiazole Crystals // Molecules. 2026. Vol. 23. P. 884. https://doi.org/10.3390/molecules31050884

This work was supported by Russian Science Foundation (project № 22-13-00255-П), https://rscf.ru/en/project/22-13-00255/