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

Abstract

Increasing the signal-to-noise ratio is one of the major goals in the field of NMR spectroscopy. In this proof of concept, we accelerate relaxation during an NMR pulse sequence using photo-generated paramagnetic states of an inert sensitizer. For the follow-up acquisition period, the system is converted to a diamagnetic state. The reversibility of the photo-induced switching allows extensive repetition required for multidimensional NMR. We thus eliminate the obstacle of line-broadening by the presence of paramagnetic species. In this contribution, we show how cycling of synchronized light/pulse sequences leads to an enhanced efficiency in multidimensional NMR. Our approach utilizes a molecular spin switch reversibly altering between a paramagnetic and diamagnetic state.

Sample illumination device facilitates in situ light-coupled NMR spectroscopy without fibre optics

“…In situ illumination of samples opens up a realm of potential light-sensitive experimental systems which may be studied by high-resolution NMR spectroscopy, one of the most powerful analytical techniques. Although a range of illumination strategies have been previously suggested, including guiding external light sources with optical fibres 29 , 30 , 47 , or modifying the NMR probe itself 20 , 21 , 27 , 34 , these solutions are generally cumbersome to use at higher throughputs, or require customised probes. Here, we present a new universal and convenient approach to illuminating NMR samples in situ with the LED-based NMRtorch device, which should be compatible with any typical NMR probehead, including cryoprobes.…”

“…Recently, the rapid development and availability of inexpensive and powerful light-emitting diodes (LEDs) with a wide choice of emission wavelengths has led to their increasing use as light sources in photo-NMR 12 , 13 , 30 – 33 . Although NMR probe modifications to incorporate LED illumination directly inside the probehead have been suggested 27 , 34 , optical fibres (either alone or inside a coaxial insert) are still typically used to guide light from the LED positioned outside the NMR spectrometer to the NMR sample inside the magnet. However, these setups also suffer from the same disadvantages inherent to the LASER-fibre optic system, with the additional difficulty of coupling poorly collimated light from an LED into a thin optical fibre, leading to significant light intensity losses 12 , 30 .…”

Molecular Spin State Switching and Photochromism in the Red and Near Infrared with Ni(II) Chlorin and Ni(II) Bacteriochlorin

“…It was estimated that several thousand spin centers must interact to achieve bistability (switchability). − The solid state nature of spin crossover materials, however, restricts the number of technical applications, and most importantly, it prevents usage in biological environments. Spin state switching of individual molecules on surfaces and in solution at room temperature is still challenging, and to date, only a few examples have been described in the literature. ,,− Molecular spin state switches open a number of technical applications in NMR, − MRI, , and light-controlled magnetic levitation . The molecular spin state switches developed in our group (Figure b,c) combine two units: a photoswitch (tone arm) including a ligand (needle) and a Ni-porphyrin (disk).…”

Synthesis of 4-substituted azopyridine-functionalized Ni(II) porphyrins as molecular spin switches

“…Molecular spin switches operated with visible light in homogeneous solution [1] or on surfaces [2], hold promise for a number of hitherto unprecedented applications such as switchable contrast agents [3][4][5][6][7], switchable NMR relaxation agents [8][9][10], and building blocks for molecular spintroncis [11]. Our modular design is based on three components: a) a Ni II -porphyrin (square planar base complex), b) an azoaryl unit (photoswitchable ligand) and c) a molecular linker or tether (connecting the porphyrin with the switchable ligand).…”