Following a Photoinduced Reconstructive Phase Transformation and its Influence on the Crystal Integrity: Powder Diffraction and Theoretical Study

Abstract

In the course of solid-state photoreactions, a single crystal (SC) of the reactant can be transformed into an SC of the product or it can lose crystallinity and become amorphous. In-between these two scenarios exist the reconstructive phase transformations, where upon irradiation, the reactant SC becomes a powder or an SC with increased mosaicity. We present a detailed description of reconstructive photodimerization, where the structural changes are directly correlated with the disintegration process. The kinetics of the reaction is explained by two kinetic regimes, forming an autocatalytic autoinhibition photoreaction set with high quantum yield. In addition, the photoreaction pathways were studied theoretically.

Metal-Free [2 + 2]-Photocycloaddition of (Z)-4-Aryliden-5(4H)-Oxazolones as Straightforward Synthesis of 1,3-Diaminotruxillic Acid Precursors: Synthetic Scope and Mechanistic Studies

“…The cyclobutane rings in these compounds are planar, as it is usually observed for other cyclobutanes containing this arrangement of groups, as are, for instance, the alpha-isomers of the truxillic acid and their related derivatives. 25,[30][31][32] In all cases, the values of the internal parameters for bond distances (Å) and bond angles (°) are as expected, and they do not show unusual deviations from values found in the literature for related structural arrangements. 15,19,25,[28][29][30][31][32][33] Revised manuscript.…”

“…[22][23][24] Very recently, the same group noticed the dimerization of 5(4H)-oxazolones in solid state ( Figure 3c, right part), in just a single case where the topochemical conditions of intermolecular C-C distances shorter than 4.2 Å (Schmidt criterion) are accomplished. 25 Therefore, sparse results have been obtained previously in this area, since each attempted irradiation has given a different result.…”

Cooperative Photochemical Reaction Kinetics in Organic Molecular Crystals

“…They concluded that the reason for the change in n is that the strain of the reaction was released and the volume of the unit cell suddenly increased during the reaction. Moreover, they also reported that tracking the photochemical reaction of crystalline benzylideneoxazolone ( 12 ) by PXRD yielded an n value that decreased from 1.1 to 0.33 due to the loss of crystallinity [38] . These are two examples in which the reaction rate slowed down due to the collapse of the crystal structure associated with the accumulation of strain.…”

“…Moreover, they also reported that tracking the photochemical reaction of crystalline benzylideneoxazolone ( 12) by PXRD yielded an n value that decreased from 1.1 to 0.33 due to the loss of crystallinity. [38] These are two examples in which the reaction rate slowed down due to the collapse of the crystal structure associated with the accumulation of strain.…”