Tuning of the Coordination and Emission Properties of 4-Amino-2,1,3-Benzothiadiazole by Introduction of Diphenylphosphine Group

Abstract

A novel amino-benzothiadiazole bearing diphenylphosphine groups (L) was designed and synthesized. A number of its coordination compounds of Cu(I) (1•0.75C 7 H 8 , 2a,b), Pd(II) (4), and Pt(II) (5) were prepared demonstrating the coordination of L ligand via N and/or P atoms. The reaction with strong Lewis acid Zn(II) resulted in the rearrangement of PNP to P−P−N moiety and formation of complex 3. The structures of L, 2−5 were determined by single crystal X-ray (XRD) diffraction, while that of 1•0.75C 7 H 8 was determined by powder XRD analysis. Intermolecular secondary bonding of S•••S interactions in the compounds, unusual for benzothiadiazoles, was discussed supported by quantum chemical calculations. Differences in the structures of the compounds cause significant changes of photophysical properties. In particular, the position of the electronic absorption band is featured by the conformation of L, viz., the dihedral angle between the benzothiadiazole unit and the PNP moiety, as proved by TD-DFT calculations performed on model molecules. The photophysical properties of the compounds also strongly depend on the coordination mode of L: the presence of a bond between the metal and the N atom of the thiadiazole unit plays an essential role in defining the position of the absorption and emission bands as well as emission lifetime of these compounds. The thermally activated delayed fluorescence and phosphorescence mechanisms in a thermal equilibrium were determined for 1• 0.75C 7 H 8 . Complex 5 features a broad emission band spanning the entire visible region; moreover, it shows an unusual clear-white luminescence, which remains visible even in the daylight.

Structural and Photophysical Properties of 2,1,3-Benzothiadiazole-Based Phosph(III)azane and Its Complexes

“…The intermolecular distances between adjacent N and S atoms lie in the range 3.04-3.51 Å. These distances are consistent with the literature data for secondary bonding interactions between btd moieties [24,26,27]. In H 2 L, two crystallographically independent types of N•••S contacts are observed: the first type links the molecules into a chain via single interactions (Figure 3, on the right), while the second links via double ones (Figure 3, on the left).…”

“…Consequently, the low-energy transitions can be described as a charge transfer from the amino group to the btd fragments. The position of the long wavelength absorption and emission bands of H 2 L and (Ph 2 P) 2 N-btd is similar, although the latter is rather characterized by a charge transfer from PPh 2 to btd [24]. According TD-DFT calculations, the low-energy bands of the coordination compounds arise from ligand-centered transitions.…”

“…Compared to H 2 L, this band is bathochromically shifted in the case of compounds 2•nC 7 H 8 , while it is hypsochromically shifted for compound 3•THF, although the latter features a broad low-intensity shoulder spanning the range of 500-600 nm. This behavior can be explained by different coordination types of H 2 L. Recently we have shown that for compounds with NH 2 -btd and (Ph 2 P) 2 N-btd ligands coordinated via N 1 atom, the absorption and emission band maxima are bathochromically shifted compared to the corresponding free btds [11,24]. This tendency is observed for a number of Cu(I), Zn(II), Ag(I), Cd(II), Pd(II) and Pt(II) complexes studied; the nature of the metal and conformation of the ligand affects the position of the bands to a lesser extent.…”

“…Recently, we reported the study of the phosphorylated 4-amino-2,1,3-benzothiadiazole derivative − N,N-bis(diphenylphosphanyl)-2,1,3-benzothiadiazol-4-amine ((Ph 2 P) 2 N-btd) (Scheme 1) and its transition-metal complexes [24]. This ligand contains one btd moiety and tends to coordinate in a bidentate manner via two P atoms.…”

Unexpectedly Long Lifetime of the Excited State of Benzothiadiazole Derivative and Its Adducts with Lewis Acids

“…2,1,3-benzothiadiazole and, in particular, its amine derivatives are able to bind with Lewis acids owing to the donor N atoms of the heterocycle and amino group [ 13 ]. Further functionalization of the derivatives with donor groups allows one to expand the set of Lewis base centers [ 14 ]. For instance, a number of coordination compounds with btd ligands bearing diphenylphosphine [ 14 , 15 ], pyridyl [ 16 , 17 ], triazolyl and pyrazolyl [ 18 ] groups were synthesized.…”