A fluorescent paramagnetic Mn metal-organic framework based on semi-rigid pyrene tetra-carboxylic acid: sensing of solvent polarity and explosive nitroaromatics.

Alankriti Bajpai,Jarugu Narasimha Moorthy,Savitha Govardhan,Arindam Mukhopadhyay,Manchugondanahalli Shivakumar Krishna

doi:10.1107/s2052252515012506

Alankriti Bajpai, Jarugu Narasimha Moorthy + Show 3 more

Open Access

https://doi.org/10.1107/s2052252515012506

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Journal: IUCrJ	Publication Date: Aug 14, 2015
Citations: 35	License type: CC BY 2.0 UK

Affiliation: Indian Institute of Technology Kanpur

Abstract

An Mn metal-organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt's solvent polarity parameter (E T (N)). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.

Highlights

Ma and co-workers have shown that gradual postsynthetic metal node metathesis of a Cd-Metal–organic frameworks (MOFs) with Mn2+ ions leads to a corresponding reduction in the fluorescence quantum yield of the Cd-MOF from 74.8 to 9.7% (Ma et al, 2013)
A number of LMOFs have been reported over the past decade or so, we are unaware of any LMOF based on a paramagnetic metal ion having been explored for sensing applications
We were motivated to explore the luminescence properties of an Mn metal–organic framework (Mn-MOF) constructed from a rationally designed pyrenebased fluorescent organic linker. We chanced upon this Mn-MOF during our persistent, but unsuccessful, attempts aimed at accessing porous fluorescent MOFs from a brilliantly fluorescent pyrene-tetraacid linker with d10 metal ions

Summary

Introduction

Metal–organic frameworks (MOFs) are a fascinating class of crystalline porous materials, which are being explored intensely for diverse applications such as gas storage (Britt et al, 2008; Murray et al, 2009; Makal et al, 2012; Suh et al, 2012; Furukawa et al, 2013), separation (Sumida et al, 2012; Li et al, 2012; Wu, Gong et al, 2012; Wu, Wang et al, 2012; Nugent et al, 2013), heterogeneous catalysis (Lee et al, 2009; Ma et al, 2009; Yoon et al, 2012; Moon et al, 2013), optoelectronics (Wang et al, 2012; Zhang & Xiong, 2012), energy storage and conversion (Li et al, 2011; Shimizu et al, 2013; Sun et al, 2013), and drug delivery and bio-imaging (Rocca et al, 2011; Horcajada et al, 2012). A number of LMOFs have been reported over the past decade or so, we are unaware of any LMOF based on a paramagnetic metal ion having been explored for sensing applications. Against this backdrop, we were motivated to explore the luminescence properties of an Mn-MOF constructed from a rationally designed pyrenebased fluorescent organic linker (see below). We were motivated to explore the luminescence properties of an Mn-MOF constructed from a rationally designed pyrenebased fluorescent organic linker (see below) We chanced upon this Mn-MOF during our persistent, but unsuccessful, attempts aimed at accessing porous fluorescent MOFs from a brilliantly fluorescent pyrene-tetraacid linker with d10 metal ions

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