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

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.

Disentangling the complex photodynamics of mixed-linker Zr-MOFs – efficient energy and charge transfer processes

“…44 The composition of ZrMOF-630 and ZrMOF-640 with a push–pull organic linker (NACDC) with an electron donor (–NH 2 ) and acceptor (–CN) pair in its molecular unit, causes a red-shift in the absorption spectra compared to the Zr-NADC MOF (having a monofunctionalized linker with only an –NH 2 group) due to stronger charge transfer (CT) character of the former. 47…”

“…It is also worth to note that the maximum of emission for both ZrMOFs in DCM suspension is significantly red-shifted (∼530–540 nm) in comparison to the emission spectrum of the pristine NACDC linker in DCM (506 nm). 47 On the other hand, it is similar to the one reported for NACDC in more polar solvents, such as acetonitrile (ACN) (542 nm) and methanol (MeOH) (559 nm), 47 which could be explained by two facts: (i) in the studied materials, the linker might experience local environments with polarity similar to ACN and MeOH, especially attending the Zr-oxo-hydroxo composition of the secondary building units (SBUs) and; (ii) the NACDC might undergo an efficient LCCT interaction with the metal clusters, which produces a red-shift in the emission spectrum as previously demonstrated. 34,36 In order to shed light on the working mechanism, we have explored the possible correlation between the MOFs’ spectroscopic properties and the solvent polarity, by recording the emission spectra of ZrMOF-630 in diethyl ether (DE) and MeOH suspensions.…”

“…General MOFs preparation: ZrCl 4 (0.4 g, 1.7 mmol) was dispersed in dimethylformamide (DMF) (75 mL) by ultrasonication at 50–60 °C. A DMF solution (25 mL) of naphthalene-2,6-dicarboxylic acid (NDC, 323 mg, 1.5 mmol) and 4-amino-8-cyanonaphthalene-2,6-dicarboxylic acid 47 (NACDC, 43 mg, 0.17 mmol) was added to previous prepared ZrCl 4 solution and, then modulator (acetic acid: 5.2 mL, 92 mmol, for ZrMOF-630, or benzoic acid: 6.3 g, 52 mmol, for ZrMOF-640) and water (0.120 mL, 0.007 mmol) was added to the mixture. The tightly capped flask was sonicated at 60 °C and kept in a bath at 120 °C under static conditions for 24–48 h. Then, the solution was slowly cooled to room temperature and the precipitate was isolated by centrifugation.…”

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…This area is the largest in terms of the number of related publications and includes 91 articles, namely [ 1 , 2 , 3 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 , 151 , 152 , 153 ,…”

“…The last one seems to be the most detailed, and it is precisely this that we will try to implement in the course of our narrative. As it should be expected, a priori, most of the publications in this direction are devoted to organic compounds, and primarily organic molecules; these include, with varying degrees of correctness, publications [ 1 , 2 , 3 , 102 , 103 , 104 , 106 , 108 , 112 , 117 , 118 , 119 , 121 , 124 , 127 , 128 , 130 , 131 , 132 , 133 , 135 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 146 , 147 , 148 , 151 , 153 , 154 , 156 , 157 , 164 , 165 , 166 , 168 , 171 , 172 , 174 , 176 , 178 , 180 , 183 , 185 , 186 ]. Much less space is occupied by the works related to polymeric (in fact, to a high molecular weight) compounds [ 113 , …”