Appending ionic liquids to fluorescent benzothiadiazole derivatives: Light up and selective lysosome staining

A Cooperative Photoactive Class-I Hybrid Polyoxometalate With Benzothiadiazole–Imidazolium Cations

“…All of the [BTD-4,7-ImH] 2+ cations show significant deviation from planarity due to the presence of strong hydrogen bond acceptor groups on both the POM (terminal oxo) and the solvent (amide oxygen); in general, the degree of ring twisting shows a positive correlation with the number of hydrogen bonds that the imidazolium ring forms ( Supplementary Tables 4, 5 ). For comparison, the crystal structure of [BTD-4,7-ImH]Cl 2 , which has been published previously (Souza et al, 2020 ), shows each imidazolium ring making multiple hydrogen bonding contacts with proximal chloride anions, giving large ring torsion angles ( Supplementary Figure 7 ). The presence of hydrogen bonding contacts between the POM and the organic cation that alters its structure demonstrates that the two components interact strongly in the solid state.…”

“…However, the tailing of the lower-energy absorption in the solution state is not reflected in the solid state. This may be due to the slight distortion of the BTD-4,7-ImH molecules in the crystalline salt ( Supplementary Figure 7 ) (Souza et al, 2020 ). With this in mind, we note that solution-phase analysis alone in the preparation of hybrid materials can at times paint only half of the picture, particularly when targeting potential applications in heterogeneous photocatalysis.…”

“…Due to the reported fluorescent properties of [BTD-4,7-ImH]Cl 2 in the solution (Souza et al, 2020 ), we were interested in investigating the fluorescence properties of the organic di-cation and the POM hybrid material 1 in the solid state ( Figure 6 ). K 6 P 2 W 18 O 62 shows no fluorescence in the solid state, whereas [BTD-4,7-ImH]Cl 2 shows a fluorescence peak at 435 nm with relative intensity of 2.41 × 10 6 cps when excited at its absorption maxima (310 nm), giving a Stokes shift of 125 nm.…”

“…All reagents and solvents were purchased in high-purity grade from commercial sources and used without further purification. The preparation and characterization of K 6 P 2 W 18 O 62 and [BTD-4,7-ImH]Cl 2 were conducted according to previous reports (Contant et al, 1990 ; Souza et al, 2020 ). Nuclear magnetic resonance (NMR) spectroscopy was performed on a Bruker AV400 spectrometer at 298 K. Attenuated total reflectance–Fourier-transform infra-red (ATR-FTIR) spectroscopy was recorded on a Bruker Tensor 27 spectrometer equipped with a Pike GladiATR module.…”

“…Derivatives of BTD have been widely used as components in organic light-emitting diodes (OLEDs) (Fell et al, 2019 ) and organic solar cells (OSCs) (Yuan et al, 2019 ) as well as in bioimaging (Neto et al, 2015 ) and fluorescence sensing (Zhang et al, 2017 ). Recently, cationic BTD derivatives flanked by imidazolium moieties have shown impressive optical properties and were used as fluorescent lysosome-staining agents (Souza et al, 2020 ). The use of imidazole flanking groups on the photoactive core allowed for the formation of cationic derivatives without compromising the photoactivity of the system; such a motif would be highly intriguing as components of Class I hybrid POMs to form photoactive materials.…”