# Get a better glimpse on sequential photoreactions of trisnorbornadienes with 19F NMR spectroscopy

## TL;DR

This paper shows how 19F NMR spectroscopy can track complex chemical reactions in a solar energy storage molecule with high clarity.

## Contribution

The use of 19F NMR spectroscopy to unambiguously identify photoreaction intermediates in trisnorbornadienes is novel.

## Key findings

- 19F NMR spectroscopy successfully identified all photoproducts in sequential photoreactions.
- The trisnorbornadiene was almost fully converted into trisquadricyclane under irradiation.
- 19F NMR overcomes signal overlap issues seen in 1H NMR and photometry for these reactions.

## Abstract

It is shown exemplarily with a trifluorinated trisnorbornadienylbenzene that 19F NMR spectroscopy may be applied as a useful complementary method for the investigation of sequential photoreactions. The trisnorbornadiene core structure was used as it figures as promising scaffold for molecular solar thermal (MOST) energy storage. The target compound was readily synthesized by a Suzuki–Miyaura coupling reaction and examined with respect to the key properties for MOST applications. Upon direct or photosensitized irradiation, the trisnorbornadiene was transformed stepwise and almost quantitatively into the corresponding trisquadricyclane. Even though the reaction can be monitored by photometry or by in situ 1H NMR spectroscopy, unambiguous assignment of the distinct intermediate mono- and bisquadricyclanes was not possible because of signal overlap. In contrast, this shortcoming is circumvented with in situ 19F NMR-spectroscopic analysis. Contrary to the 1H NMR spectra, the 19F NMR spectra show significantly fewer characteristic and sufficiently separated signals that allow the unambiguous identification of all photoproducts and, thus, their detection in the course of the photoreaction.