Studies of a photochromic model system using NMR with ex‐situ and in‐situ irradiation devices

Abstract

The switching behavior of a photochromic model system was investigated in detail via NMR spectroscopy in order to improve understanding of the compound itself and to provide ways to obtain insights into composition trends of a photo switchable (polymeric) material containing spiropyran/merocyanine units. In addition to the classical irradiation performed outside the magnet (ex-situ), a device for irradiation inside the NMR spectrometer (in-situ) was tested. Both setups are introduced, their advantages and disadvantages as well as their limits are described and the setup for future investigations of photochromic materials is suggested. The influence of different sample concentrations, irradiation procedures, and light intensities on the model system was examined as well as the dependence on solvent, temperature, and irradiation wavelengths. Using the recently published LED illumination device, it was even possible to record two-dimensional spectra on this model system with rather short half-life (7 min in DMSO). This way (13) C chemical shifts of the merocyanine form were obtained, which were unknown before. Copyright © 2016 John Wiley & Sons, Ltd.

Combined In Situ Illumination‐NMR‐UV/Vis Spectroscopy: A New Mechanistic Tool in Photochemistry

“…In our previous study about photoswitchable spiropyrans, deviations between the quantitative data of UV/Vis and NMR spectroscopy were found, demonstrating the importance of identical light intensities and reaction vessels in separated setups 18. To demonstrate the advantages of our UVNMR‐illumination setup with only one illumination device and a common reaction vessel, a spectroscopic analysis of a similar photoswitchable spiropyran is presented.…”

A Versatile Approach for In Situ Monitoring of Photoswitches and Photopolymerizations

“…Alternatively, direct illumination and monitoring has been accomplished within an NMR spectrometer,e ither by installing al ight source inside the instrumento ru sing an optical fiber,w hich typically requires probe modificationo racoaxial glass insert, respectively. [31][32][33][34][35][36][37][38][39][40][41][42][43] The use of light-coupled optical fibers with NMR spectroscopy has distinct advantages from the standpoint of technical simplicity,c ompatibility with aw ide radiation range (UV-IR), and relativelyl ow cost (comparedt op robe modifications). Apart from traditional coaxial capillaryi nserts, "pencil tip" inserts [38,39] and fiber-tipe tching procedures [31,33] have been utilized to pro-As imple, inexpensive, and modularm ethod to directly illuminate NMR samples for in situ analysis of photochemical transformations is reported.T he versatility of this technique is demonstrated by analyzing the light-induced propagating front for small-molecule photoswitchesa nd the kinetics of photocontrolled living radical polymerizations.…”

Speeding up NMR by in Situ Photo‐Induced Reversible Acceleration of T1‐Relaxation (PIRAT)

“…Before the next scan/increment, the spin switch is reverted to its “silent” ( S= 0) state with blue light. Several setups for in situ irradiation of samples inside NMR spectrometers have been reported in the recent time and are continuously optimized.…”

“…During the pulse sequence and data acquisition (indicated by black boxes and FID) the spin switch rests in its diamagnetic state ((E)-1, S = 0), and is paramagnetic ((Z)-1, S = 1) duringt he relaxation delay.with blue light. Severals etups for in situ irradiation of samples inside NMR spectrometers have been reported in the recent time [22][23][24][25][26] and are continuouslyoptimized.The principle behind our approachi si llustrated in Figure 2, where we follow the z-magnetization recovery after the final 908 pulse(black rectangle) of ap ulses equence. Theblue curve represents the z-magnetization of asample containing diamagnetic (E)-1.…”

“…with blue light. Severals etups for in situ irradiation of samples inside NMR spectrometers have been reported in the recent time [22][23][24][25][26] and are continuouslyoptimized.…”