The question of whether sound vibration of a medium can bring about any kind of molecular or macromolecular events is a long-standing scientific controversy. Although it is known that ultrasonic vibrations with frequencies of more than 1 MHz are able to align certain macromolecules in solution, no effect has yet been reported with audible sound, the frequency of which is much lower (20-20,000 Hz). Here, we report on the design of a supramolecular nanofibre that in solution becomes preferentially aligned parallel to the propagation direction of audible sound. This phenomenon can be used to spectroscopically visualize sound-induced vibrations in liquids and may find application in a wide range of vibration sensing technologies.

"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

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] the [ZnP() 1 ] monomer adopts exclusively a planar conformation in its cyclic tetramer ([{ k ZnP() 1 } 4 ]), while longer alkynylene versions [{ZnP( ) n } 4 ] (n = 2, 4) exist as a mixture of the two conformationally isomeric tetramers [{ ? ZnP( ) n } 4 ] and [{ k ZnP( ) n } 4 ]. The cyclic tetramers composed of [ ? ZnP() n ] are chiral, and that with n = 4 ([{ ? ZnP() 4 } 4 ])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...

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… has been used to discriminate nonpolar solvents by using a self-assembled chromophoric molecule. A. Tsuda, T. Aida, and co-workers describe in their Communication on page 5153 ff. the self-assembly of a bis(zinc pyridylporphyrin) rotamer with a p-conjugated linker to give a mixture of supramolecular boxes composed of planar and perpendicular conformers. The ratio of the two boxes changes depending on the solvent, and leads to a solvatochromic response.