Probing chemical transformations in organic solids via NMR techniques: The solid-state photodimerization reaction of 7-methoxy-4-methylcoumarin

Abstract

It has been reported that crystalline 7-methoxy-4-methylcoumarin undergoes a [2 + 2] photodimerization reaction to give two different products; the major product is the syn head-head dimer, whereas the minor product is the syn head-tail dimer. In this paper, high-resolution solid-state 13C NMR and solution-state IH and ~3C NMR techniques have been applied to investigate various structural issues relating to this solid-state photodimerization reaction. In particular, spectra have been recorded at various stages during the progress of the photodimerization reaction with the aim of charting the structural changes in the system as a function of reaction progress, with particular interest in assessing the potential of this technique for investigating the structural reasons for the production of the minor product. Conformational and dynamic properties of the product obtained in this solid-state photodimerization reaction have also been assessed.

Synthesis and Photochemistry of Coumarin-Based Self-Assembled Monolayers on Silicon Oxide Surfaces

“…Since then, coumarin and its 7-alkoxy derivatives have been extensively studied due to their unique photochemistry. Besides the enormous number of studies on homogeneous solutions, − there are also publications on photochemical behavior in crystals − and polymer matrices such as thin films. , Under irradiation of light having a wavelength longer than 300 nm, coumarin and its 7-alkoxy derivatives are able to dimerize in four possible stereo isomers: syn or anti head-to-head (hh) and syn or anti head-to-tail (ht), respectively. Using light of a wavelength shorter than 300 nm photocleavage is observed as shown in Scheme for 7-(11-trichlorosilylundecyloxy)coumarin ( 1 ).…”

Self-Assembled Monolayers of 7-(10-Thiodecoxy)coumarin on Gold: Synthesis, Characterization, and Photodimerization

“…Photodimerization of coumarin and its derivatives has been extensively studied in homogeneous solution , and in organized media such as micelles, − cyclodextrin inclusion complexes, and crystals. − Upon irradiation with wavelengths longer than 300 nm in solution, coumarin derivatives are generally converted to four regioisomeric photodimers (the syn head-to-head (H-H), syn head-to-tail (H-T), anti head-to-head, and anti head-to-tail dimers) through a [2 + 2] photocycloaddition, as shown in Scheme for 7-(10-thiodecoxy)coumarin .…”

Bridging photochemistry and photomechanics with NMR crystallography: the molecular basis for the macroscopic expansion of an anthracene ester nanorod

“…In this article, we describe a new approach that combines ensemble oriented-crystal NMR spectroscopy and first-principles computational chemistry to determine the absolute unit cell orientations relative to the shape change in a photoreactive, molecular crystal, 9TBAE nanorod. Solid-state NMR (SSNMR) has been used to study a number of solid-state photochemical transformations, 25,38,[40][41][42][43][44][45][46][47][48][49][50][51][52] and foundational work by Nieuwendaal, Hayes and coworkers 53 demonstrated how single-crystal NMR could be used to determine the relative orientation of the reactant and product in the single-crystal to single-crystal topochemical photoreaction of trans-cinnamic acid. Our work builds on this approach and for the first time uses SSNMR to tie the atomic-level structural rearrangement of the reacting molecular species to the mechanical response of a nanostructured sample.…”