Studies on dynamics and isomerism in supercooled photochromic compound Aberchrome 670 with the use of different experimental techniques

Abstract

Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and Broadband Dielectric (BD) spectroscopies were applied to investigate the thermal, structural, photochemical and dynamical properties of a fulgide-type photochromic compound, Aberchrome 670 (Ab670). In the original crystals, characterized by a pale yellow color, molecules take the E conformation. However, upon UV irradiation of either the crystalline or glassy compound, it isomerizes to the closed (C) form, characterized by the intense red tone. Although, we have found that such conversion is not complete (far below 100%). It was shown that due to UV irradiation as well as heating of the studied fulgide to high temperature (above the melting point), the Z isomer is formed. Further FTIR measurements performed on the UV irradiated and molten compound indicated that upon annealing of the sample in the vicinity of the glass transition temperature the Z isomer reverts back to the original E form. The final confirmation of this supposition has come from BDS studies, where the strong shift of the structural relaxation process during time-dependent isothermal measurements was noticed. One can add that a similar pattern of behavior has been observed previously by some of us in the case of tautomerism or mutarotation [Z. Wojnarowska et al., J. Chem. Phys., 2010, 133, 094507; W. Kossack et al., J. Chem. Phys., 2014, 140, 215101; P. Wlodarczyk et al., J. Phys. Chem. B, 2009, 113, 4379-4383; P. Wlodarczyk et al., J. Non-Cryst. Solids, 2010, 356, 738-742]. From the analysis of the time variation of the structural relaxation times, the activation barrier, E = 18 kJ mol, for Z to E isomerization in Ab670 was calculated. Interestingly, it agrees well with the one determined for a similar kind of transformation in stilbenes. Therefore, we found that dielectric spectroscopy can be a very useful technique to track Z to E interconversion in the highly viscous supercooled state. Consequently, a unique opportunity to follow this kind of isomerism at high pressures, high electric fields and under nanometric spatial confinement in pure supercooled compounds appeared.

Impact of Amorphization Methods on the Physicochemical Properties of Amorphous Lactulose

“…Moreover, the variation of T g with changes in the tautomeric composition due to solid-state mutarotation is not specific to sugars. It was also noticed in some drugs like glibenclamide and aberchrome 670 and in some polymers like azopolymers (polymers containing azobenzene) where mutarotation (photoisomerization) can be interestingly triggered by UV irradiation . All of these materials have thus the interesting property to have a tunable T g , which can be varied by some external physical parameters.…”

Nanoporous Metal–Organic Framework Thin Films with Embedded Fulgide for Light-Modulated Guest Adsorption and Diffusion

“…To get further insights into the photoisomerization of Aber670 in the UiO-68 pores, the vibrational infrared reflection-absorption (IRRA) spectra were recorded before and after irradiation by UV and green light (Figure ). The IRRA spectra show characteristic peaks of −C–O, O–C–O, and −CO stretching vibrations at 924 cm –1 , 1226 cm –1 , and 1755–1818 cm –1 , respectively (Figure b), indicating the presence of Aber670 inside the MOF. , The reference IR spectra of pure Aber670 are shown in the Supporting Information, Figure S2. Upon UV irradiation, significant changes of the intensities of the peaks in correlation with fulgide in the MOF pores were observed; in particular, the intensities of the peaks at 924 cm –1 , 1226 cm –1 , and 1755–1818 cm –1 decrease (see Figure b).…”

Paving the Way to the First Functional Fulgide@MOF Hybrid Materials

“…For Aberchrome 670, only little IR data are published on both the initial and the irradiated state: Kaminśki and co-workers studied the photochromic behavior via various spectroscopic methods of the fulgide under supercooled conditions. 44 Via experimental and theoretical data, the authors mainly identified the occurrence of a strong band at 1514 cm −1 after UV light irradiation, which they attributed to a υ CC vibration of the C-form. In addition, Gustav and co-workers recorded changing vibrational modes of Aberchrome 670 after UV light exposure in the dissolved state.…”

“…∼1246 cm −1 occurs. With application of the experimental and theoretical data of Kaminśki and co-workers 44 and, additionally, listed IR data of Hesse, Meyer, and Zeeh, 46 the IR signatures of Aberchrome 670 in the initial and irradiated state were determined at ambient conditions inside MOF-5 and MIL-68(In). The results are listed in Tables S1 and S2.…”

“…azobenzenes and derivatives ,, as well as to determine the IR signatures of thermodynamically unstable isomers (spiropyrans and spirooxazines). For Aberchrome 670, only little IR data are published on both the initial and the irradiated state: Kamiński and co-workers studied the photochromic behavior via various spectroscopic methods of the fulgide under supercooled conditions . Via experimental and theoretical data, the authors mainly identified the occurrence of a strong band at 1514 cm –1 after UV light irradiation, which they attributed to a υ CC vibration of the C -form.…”