“Conformational” Solvatochromism: Spatial Discrimination of Nonpolar Solvents by Using a Supramolecular Box of a π‐Conjugated Zinc Bisporphyrin Rotamer

Abstract

"Solvatochromism" is the ability of chromophoric molecules to change their absorption and/or luminescence colors as a result of a change in solvent polarity. [1][2][3][4][5] In principle, solvatochromic shifts are caused by a change in the energy gap between a ground state and excited state of different polarities, since a change in the solvent polarity leads to differential stabilization of these electronic states. Therefore, specific interactions between chromophore and solvent molecules result in variations in the wavelength, intensity, and shape of the absorption and/or luminescence spectra. Recent examples of particular interest include conjugated polymers that change their conformation and give rise to a solvatochromic response.[4] From this general understanding of solvatochromism, one may simply assume that the color of a chromophoric molecule hardly depends on the chemical structures of solvents when their polarities are, for example, equally very low.[5] Here we report the interesting phenomenon that a dialkynylene-bridged zinc bisporphyrin rotamer ([ZnP() 2 ]) shows an explicit solvatochromic response to nonpolar solvents with low dielectric constants (2.23-2.57). To our surprise, it can discriminate the regioisomers of xylene.Zinc complexes [ZnP( ) n ] (n = 1, 2, and 4) bearing two meso-pyridyl (Py) groups are designed to form a box-shaped cyclic tetramer in nonpolar solvents through Zn-Py coordination (Scheme 1). The assembling behavior of newly synthesized [ZnP() 2 ] was unambiguously characterized by 1 H NMR, absorption, and emission spectroscopy, along with size-exclusion chromatography (SEC; see Figure S1 in the Supporting Information).[6] As reported in previous studies, [7][8][9] has been demonstrated to sense the absolute structures of asymmetric hydrocarbon solvents. [9] In the course of these studies, we noticed that the colors of solutions of [ZnP() 2 ] in benzene and CCl 4 are quite different from one another (Figure 1 a), even though their dielectric constants are nearly identical. The absorption spectrum of a solution of [ZnP( ) 2 ] in benzene showed Soret and Q bands at 447 (S I ) and 626 nm (Q I ), respectively (Figure 1 a, green line). In contrast, the absorption profile in CCl 4 was considerably different, with the Soret and Q bands appearing at 447 (S I )/483 (S II ) and 686 nm (Q II ), respectively (Figure 1 a, red line). By reference to our previous studies on a derivative of [ZnP( ) 2 ] with TMSethynyl groups at the meso positions and of [ZnP() 4 ], [8] together with the (TD)DFT-simulated absorption bands of a dialkynylene-bridged zinc bisporphyrin reference [ZnP() 2 *] with dihedral angles of 0 and 908 (B3LYP/6-31G*; see Figure S2 in the Supporting Information), [6] the green and orange-colored absorption spectra in Figure 1 a

Solvent-dependent Assembly of Discrete and Continuous CoCl2 Adamantane-based Ligand Complexes: Observations by CSI–Mass Spectrometry and X-ray Crystallography

“…Therefore, limited studies of environment-dependent complexes have been reported up to the present. [42][43][44][45][46] Conventional MS using electron ionization, chemical ionization, fast atom bombardment, and electro-spray ionization cannot detect large coordination complexes because the weak coordination bonds dissociate during ionization. Cold-spray ionization MS (CSI-MS) is one of the most promising solutions to this problem, 47 as it can detect coordination complexes without dissociation to give the numbers of ligands and metals as well as ions based on the solvent adducts.…”

“…It should be emphasized that CSI-MS involves solvent adducts very often. 43 The assignment of observed ion peaks is summarized in Table 1. The difference in mass number between the adjacent peaks corresponds to the doubly charged adamantane-based ligand, as shown in Fig.…”

Ultrafast Energy Transfer in Biomimetic Multistrand Nanorings

“…15 Coordination of the pyridyl substituents to the zinc metal centers drives the self-assembly of the complexes, as shown in Figure 1. The ring–dimer complex c -P12·(P2py2) 6 (Figure 1a) consists of a porphyrin nanoring and six P2py2 dimers; these free-base porphyrin dimers have one meso -4-pyridyl substituent on each porphyrin unit to coordinate to the zinc centers of the nanoring.…”

Oligoporphyrins with One-and Two-Atom Covalent Bridges: Synthesis and Reactivity, Solid-State, Solution and Electronic Structures, Spectroscopy and Applications

“…216,217 Their approach was to use 10-(4-pyridyl)-20-(3,5-dialkoxyphenyl)porphyrin dimer 66 as precursor; like the N 2 -linked corner porphyrin dimers 86a and 86b, 104 syn-planar and anti-planar conformers exist. Insertion of Zn(II) induces the formation of the "orthogonal" and "planar" forms of the boxes, by self-complementary coordination of the lateral 4-pyridyl N to the central Zn atom of another molecule.…”