Products Cited in Publications Worldwide Optical properties of porphyrin aluminum metal-organic frameworks by “conventional” and synchronous luminescence spectroscopy, and effect of sorption of diethyl sulfide

Optical properties of porphyrin aluminum metal-organic frameworks by “conventional” and synchronous luminescence spectroscopy, and effect of sorption of diethyl sulfide

Ahmad, Mohammad Shahwaz; Samokhvalov, Alexander

DOI:

Abstract

(MOFs) are advanced structured coordination polymers that contain metals and organic linkers and feature interesting optical properties. Particularly, MOFs with linkers of complex structure, which absorb and emit light in the optical range, are promising for opto-electronics, chemo-sensing toxic vapors and liquids, sorption-based removal of hazardous compounds, and beyond. Here, we report studies of optical properties of two porphyrin MOFs using “conventional” excitation-emission matrix (EEM) spectra, from the near-UV through visible and into the near-infrared (NIR) range. Namely, the porphyrin aluminum MOF without metal in the porphyrin ring, compound 2 actAl-MOF-TCPPH2 absorbs light in the near-UV range due to the Soret band and, additionally, throughout the visible range. Its photoluminescence (PL) occurs in the NIR range via the purely electronic Q(0-0) and the first vibronic Q(0-1) bands. Further, the related compound 4 actAl-MOF-TCPPCu with Cu2+ cation in the porphyrin ring exhibits a strong, a factor 50 quenching of the PL signal, due to the paramagnetic copper cation. Nevertheless, it shows the characteristic emission via both the Q(0-0) and Q(0-1) bands. Further, compound 4 adsorbs vapor of volatile organic sulfur compound diethyl sulfide (DES), forming the stoichiometric absorption complex. Binding DES to the metalloporphyrin ring in this complex is detected based on the EEM spectra. Next, the common drawbacks of the EEM spectra, e.g. wide and overlapping emission bands and peaks due to diffraction grating artifact, have been overcome by the advanced method. Namely, the solid-state synchronous luminescence spectroscopy (SS-SLS) allows to successfully resolve both Q-bands in these MOFs and remove spectral artifacts. Additionally, the SS-SLS allows to get insight into the origin of an additional NIR emission band due to the interaction of each compound with molecular oxygen. For both porphyrin MOFs, the comprehensive scheme of optical (absorption and emission) transitions was obtained which includes the Soret band, two Q-bands, and the emission band involving oxygen.

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