Highly ordered chromophoric linkers positioned within the metal-organic frameworks (MOFs) have the potential to mimic natural light-harvesting complexes. Herein we report topological control over the photophysical properties of MOFs via modular interchromophoric electronic coupling to manifest different steady-state singlet emission spectra and their corresponding fluorescence lifetimes.

We show the simultaneous generation of hyperpolarized C-labeled acetate and N-labeled imidazole following spin-relay of hyperpolarization and hydrolysis of the acetyl moiety on 1- C- N -acetylimidazole. Using SABRE-SHEATH (Signal Amplification by Reversible Exchange in SHield Enables Alignment Transfer to Heteronuclei), transfer of spin order occurs from parahydrogen to acetylimidazole N atoms and the acetyl C site (≈263-fold enhancement), giving rise to relatively long hyperpolarization lifetimes at 0.3 T (T ≈52 s and ≈149 s for C and N, respectively). Immediately following polarization transfer, the C-labeled acetyl group is hydrolytically cleaved to produce hyperpolarized C-acetate/acetic acid (≈140-fold enhancement) and N-imidazole (≈180-fold enhancement), the former with a C T of ≈14 s at 0.3 T. Straightforward synthetic routes, efficient spin-relay of SABRE hyperpolarization, and facile bond cleavage open a door to the cheap and rapid generation of long-lived hyperpolarized states within a wide range of molecular targets, including biologically relevant carboxylic acid derivatives, for metabolic and pH imaging.

The present work investigates the potential for enhancing the NMR signals of DNA nucleobases by parahydrogen-based hyperpolarization. Signal amplification by reversible exchange (SABRE) and SABRE in Shield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) of selected DNA nucleobases is demonstrated with the enhancement (ε) of 1H, 15N, and/or 13C spins in 3-methyladenine, cytosine, and 6-O-guanine. Solutions of the standard SABRE homogenous catalyst Ir(1,5-cyclooctadeine)(1,3-bis(2,4,6-trimethylphenyl)imidazolium)Cl (“IrIMes”) and a given nucleobase in deuterated ethanol/water solutions yielded low 1H ε values (≤10), likely reflecting weak catalyst binding. However, we achieved natural-abundance enhancement of 15N signals for 3-methyladenine of ~3300 and ~1900 for the imidazole ring nitrogen atoms. 1H and 15N 3-methyladenine studies revealed that methylation of adenine affords preferential binding of the imidazole ring over the pyrimidine ring. Interestingly, signal enhancements (ε~240) of both 15N atoms for doubly labelled cytosine reveal the preferential binding of specific tautomer(s), thus giving insight into the matching of polarization-transfer and tautomerization time scales. 13C enhancements of up to nearly 50-fold were also obtained for this cytosine isotopomer. These efforts may enable the future investigation of processes underlying cellular function and/or dysfunction, including how DNA nucleobase tautomerization influences mismatching in base-pairing.