Switchable Aromaticity in an Isostructural Mn Phthalocyanine Series Isolated in Five Separate Redox States

Abstract

The synthesis and characterization of a new phthalocyanine (Pc) Mn-nitride complex, ( OEt Pc)MnN (2; OEt Pc = 1,4,8,11,15,18,22,, as well as its stable, readily accessible oxidized (2 + and 2 2+ ) and reduced (2 -, 2 2-) congeners is reported. This unique isostructural series displays switchable aromatic character spanning the aromatic (2), non-aromatic (2 2+ ), and antiaromatic (2 2-) triad, in addition to the open-shell radical states (2 + , 2 -). All complexes were structurally characterized and displayed significant structural distortions at the redox extrema (2 2+ , 2 2-) consistent with proposed [16 or 18]annulene  ring circuit models. Spectroscopic and computational studies further support these models. This isolated, fully characterized, isostructural series spanning five redox states (2 2+ , 2 + , 2, 2 -, 2 2-) is unique in both the Pc and related macrocyclic (ex. porphyrinoids) literature and may offer direct insight into structural-electronic correlations driven by switchable aromaticity.

Synthesis, structures and reduction chemistry of monophthalocyanine scandium hydroxides

“…These are shifted significantly upfield compared to typical Pc 2-ligand resonances, e.g., 9.53 and 8.24 ppm in PcSc(µ-Cl 2 )Li(THF) 2 (2). This upfield shift for the Pc ring proton resonances in 1 2-, to the region where non-aromatic alkene proton signals are found, reflect the partial loss of aromaticity in the Pc ring as it is reduced from an 18 π-electron aromatic Pc 2ligand to a 20 π-electron antiaromatic Pc 4species; this spectroscopic feature has been similarly reported for the doubly ring-reduced PcGe(py) 2 [33] and (OEt) 8 PcMnN [37].…”

The Contribution of Density Functional Theory to the Atomistic Knowledge of Electrochromic Processes

“…In recent years, however, the investigation has expanded to other promising organic and inorganic systems including those containing boron [ 41 , 42 , 43 ], quinodimethane derivatives [ 44 , 45 ], metal-phtalocyanine [ 46 ], metal oxides-based film [ 7 , 47 , 48 ], oligoaniline [ 49 ], antracenes [ 50 , 51 ], azacenes [ 52 ], polymethine and polyimides [ 53 , 54 ], and some organometallic complexes [ 55 , 56 ].…”

Switchable Aromaticity of Phthalocyanine via Reversible Nucleophilic Aromatic Addition to an Electron-Deficient Phosphorus(V) Complex

“…The observed reversible optical switching could pave the way to the development of molecular switches and pH sensors. 42,43 To interpret the results of NMR experiments, the nucleusindependent chemical shift, NICS(1), 22,44 and theoretical 1 H and 13 C NMR spectra were calculated for 1 + and [1+OH] using the gauge independent atomic orbital (GIAO) method 45 (Figure 4a,b and Figure S30). For 1 + substantially negative NICS(1) values are evenly distributed among subrings, which points to strong aromaticity of both the inner annulene and peripheral benzene rings.…”

“…The stabilization of nonaromatic Pc derivatives is a challenging task, which can be solved by redox reactions. Indeed, stable nonaromatic radicals or even antiaromatic species can be isolated using redox processes. − However, in all of these cases the cyclic conjugation perimeter remains intact and the aromaticity can be restored by complementary addition or removal of electrons, which renders Pcs as redox-active components of molecular materials and devices with switchable properties . Meanwhile, examples of postsynthetic modification of Pcs leading to structurally characterized stable adducts with broken conjugation remain unknown.…”