Femto- to Millisecond Time-Resolved Photodynamics of a Double-Functionalized Push-Pull Organic Linker: Potential Candidate for Optoelectronically Active MOFs.

Mario Gutiérrez,Félix Sánchez,Mercedes Pintado-Sierra,Abderrazzak Douhal,Lorenzo Angiolini,Lucie Duplouy-Armani

doi:10.3390/ijms21124366

Abstract

The design of improved organic linkers for the further engineering of smarter metal–organic framework (MOF) materials has become a paramount task for a wide number of material scientists. In this report, a luminescent double-functionalized push–pull (electron donor–acceptor) archetype organic molecule, dimethyl 4-amino-8-cyanonaphthalene-2,6-dicarboxylate (Me2CANADC), has been synthesized and characterized. The optical steady-state properties of Me2CANADC are strongly influenced by the surrounding environment as a direct consequence of its strong charge transfer (CT) character. The relaxation from its first electronically excited singlet state follows a double pathway: (1) on one side deactivating from its local excited (LE) state in the sub-picosecond or picosecond time domain, and (2) on the other side undergoing an ultrafast intramolecular charge transfer (ICT) reaction that is slowing down in viscous solvents. The deactivation to the ground state of these species with CT character is the origin of the Me2CANADC luminescence, and they present solvent-dependent lifetime values ranging from 8 to 18 ns. The slow photodynamics of Me2CANADC unveils the coexistence of a non-emissive triplet excited state and the formation of a long-lived charge separated state (2 µs). These observations highlight the promising optical properties of Me2CANADC linker, opening a window for the design of new functional MOFs with huge potential to be applied in the fields of luminescent sensing and optoelectronics.

Highlights

The design and fabrication of smarter functional materials for real-world applications has become a priority for a large number of material researchers
We have reported on the rich photodynamics of a potential linker for future metal–organic framework (MOF) engineer, Me2CANADC
We have demonstrated that the optical absorption and emission behavior of Me2CANADC is strongly influenced by the surrounding environment, owing to the excited-state charge transfer (CT) character of this molecule

Summary

Introduction

The design and fabrication of smarter functional materials for real-world applications has become a priority for a large number of material researchers. Two different carboxylate linker derivatives of 1,3,5-benzenetribenzoate were used in the fabrication of Zr-MOFs [23] The functionalization of these linkers with methyl groups forces the peripheral rings to situate perpendicularly to the central one and at the same time confers an increase in the hydrophobicity of the materials, making them more stable in water. This fact, jointly to the linker emission properties, made possible the use of these MOFs for the detection of antibiotics and organic explosive molecules in water [23]. The aforementioned linker was used in the synthesis of a Zr-based MOF, which retains the TADF properties of the linker, having this special importance for its promising potential to be applied in the generation of light-emitting diodes [26,27]

Methods

Results

Conclusion