THERMODYNAMICS OF SUBLIMATION OF INDOLINE BASED SPIROPYRANS WITH DIFFERENT POSITIONS OF THE METHOXY GROUP
Efimov F.M., Kaplin A.S., Motalov V.B., Dunaev A.M.
Ivanovo State University of Chemistry and Technology
153000, Ivanovo, Sheremetevskiy ave., 7
Spiropyrans are organic photochromic compounds used to create multifunctional materials such as optical filters, photoswitches, biosensors, and other hybrid materials. In this work thermodynamics parameters were studied at heterogeneous equilibrium for 1,3,3-trimethyl-6'-methoxy-spiro[indoline-2,2'-2H-chromene] (SP-22), 1,3,3-trimethyl-8'-methoxy-spiro[indoline-2,2'-2H-chromene] (SP-23), and 1,3,3-trimethyl-5'-methoxy-spiro[indoline-2,2'-2H-chromene] (SP-24).
The Knudsen effusion mass spectrometry was employed to obtain saturated vapor pressure and sublimation enthalpy. Since difference of structure of the compounds is the position of the methoxy group, the mass spectra of all spiropyrans are identical and has following main peaks: 159, 292, 307. The peak at m/z 307 corresponds to the molecular ion (М+), 292 to (М-CH3)+, and the ion at m/z 159 results from the cleavage of the molecule at the spiro-atom. The vapor is monomolecular since dimers and trimers were not discovered in the mass spectrum.
Above the solids the saturated vapor pressures were determined by the Knudsen effusion method, which, in combination with mass spectrometric data, allow us to recommend the following equations for the temperature dependence of pressure for each of the compounds:
SP-22: ln(p, Pa) = (-15.95±0.19)·1000/T+(41.42±0.52), ΔT = 328-373 K
SP-23: ln(p, Pa) = (-14.59±0.19)·1000/T+(38.25±0.57), ΔT = 322-348 K
SP-24: ln(p, Pa) = (-14.13±0.09)·1000/T+(36.83±0.26), ΔT = 330-372 K
The sublimation enthalpy was found using the second-law method of thermodynamics for the experimental temperature and recalculated to 298.15 K according to [1].
The thermodynamic data of sublimation
| ΔT, K | Thm, K | ΔsubH°(Thm), kJ·mol–1 | ΔsubH°(298.15), kJ·mol–1 | |
|---|---|---|---|---|
| SP-22 | 328-373 | 350 | 132.4±2.2 | 136.2±3.5 |
| SP-23 | 322-348 | 335 | 121.3±2.1 | 124.1±2.9 |
| SP-24 | 330-372 | 351 | 117.5±1.5 | 121.2±3.0 |
The first sample, in which the methoxy group is in the 6’- position, has the highest sublimation enthalpy. It correlates with the highest melting enthalpy and the lowest pressure among samples studied. The properties of SP-23 and SP-24 are similar.
1. Acree W.Jr., Chickos J.S. J Phys. Chem. Ref. Data. 2016. 45. 033101.
This work was supported by the Ministry of Science and Higher Education of the Russian Federation in the framework of Government order (project № FZZW-2026-0005).