Transient States in [2 + 2] Photodimerization of Cinnamic Acid:  Correlation of Solid-State NMR and X-ray Analysis

Abstract

13C-CPMAS and other solid-state NMR methods have been applied to monitor the solid-state reactions of trans-cinnamic acid derivatives, which are the pioneer and model compounds in the field of topochemistry previously studied by X-ray diffraction, AFM, and vibrational spectroscopy. Single-crystal X-ray analyses of photoirradiated alpha-trans-cinnamic acid where the monomers are arranged in a head-to-tail manner have revealed the formation of a centrosymmetric alpha-truxillic acid photodimer. For a centrosymmetric dimer, however, two cyclobutane carbon signals and one carbonyl carbon signal were expected apart from other aromatic carbon signals. Instead, four cyclobutane and two carbonyl carbon signals were observed suggesting the formation of a non-centrosymmetric photodimer. Removing hydrogen bonds from the system by esterfication of alpha-truxillic acid yield a centrosymmetric photodimer. Careful analysis of the obtained products via solid-state NMR clearly showed that the observed peak splittings in the 13C-CPMAS spectra did not originate from packing effects but rather result from asymmetric hydrogen bonds distorting the local symmetry. Further evidence of this rather dynamic hydrogen-bonding stems from high-temperature X-ray data revealing that only the joint approach of both X-ray analysis and solid-state NMR at similar temperatures allows for the successful characterization of dynamic processes occurring in topochemical reactions, thus, providing detailed insight into the reaction mechanism of organic solid-state transformations.

Photocrosslinkable biodegradable elastomers based on cinnamate-functionalized polyesters

“…Furthermore, cinnamic acid and the photocrosslinked dimer (α-truxillic acid) are naturally occurring bioactive compounds [32]. Photodimerization of cinnamate moieties proceeds through excitation of π electrons to antibonding molecular oribitals that ultimately form a cyclobutane ring between two adjacent molecules [33] (Scheme 1b). This mechanism in PGS-CinA networks is supported by FT-IR (Figure 2).…”

Biobased Polyimides from 4-Aminocinnamic Acid Photodimer

“…The T g values of these PIs depended on the backbone structure of the dianhydride component. 25,26 PI-1m and PI-2m exhibited no T g below 350°C, which is the measuring limit of the DSC machine, meaning that they could not determine T g values due to their decomposition temperature lower than T g phenomena. Although the sulfone group of DSDA should give flexibility to the PI-6m backbone, the PI had a higher T g than PI-3m, PI-4m, or PI-5m.…”

“…Furthermore, other peaks at 1518 cm −1 (C−C stretching of aromatic), 1441 cm −1 (CC stretching of p-substituted benzene) 1376 cm −1 , (C−N stretching of imide), and 1175 cm −1 (imide ring deformation) appeared, which indicated a complete imidization. 25 The PIs were abbreviated PI-1m, PI-1e, PI-2m, PI-2e, PI-3m, PI-4m, PI-5m, and PI-6m, whose numerals correspond with the PAAs shown in Table 1. PI-4m from OPDA showed IR peaks assigned to the C−O stretching of ether group at 1238 cm −1 , 26 and PI-6m from DSDA showed peaks assigned to asymmetric and symmetric SO stretching at 1323 and 1148 cm −1 , respectively.…”

Tween 20-cinnamic acid conjugate as a UV-absorbing emulsifier

“…The dimer of CA is formed through ((2+2) cycloaddition) under the irradiation of a UV light and the dimer can be reversibly photo-cleaved http://dx.doi.org/10.1016/j.colsurfa.2014.03.076 0927-7757/© 2014 Elsevier B.V. All rights reserved. [5,6]. Several kinds of photo-responsive carriers were developed by taking advantage of the photochemical property [7][8][9][10][11][12][13][14][15].…”