Solvatochromism of an Aminobenzodifuranone:  An Unprecedented Positive Wavelength Shift

Unique interactions between the chromophore and glutamate 16 lead to far‐red emission in a red fluorescent protein

“…For example, a positive solvatochromic shift was observed for an aminobenzodifuranone derivative (ABF) in hexamethylphosphoramide (HMPA), which was explained by a hydrogen bond between the solvent HMPA and the solute ABF, stabilizing the excited state of the solute relative to the ground state. 28 In summary, we propose that the large Stokes shift in mPlum results from the presence of and strengthening of the Glu16-chromophore hydrogen bond interaction in the excited state, which stabilizes the excited state of the chromophore relative to the ground state. As glutamine cannot fully substitute for glutamic acid, the possibility of proton transfer between Glu16 and the chromophore in the excited state remains an open question.…”

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

“…[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 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 seems essential for the observed solvatochromic response, since the absorption spectral profile of the free-base H 2 P() 2 did not vary when the solvent was changed from benzene to CCl 4 (see Figure S3 in the Supporting Information). [6] In [D 6 ]benzene at 20 8C, assembled [ZnP( ) 2 ] showed two sets of upfield-shifted signals at d 2-3.5 and 5.5-6.5 ppm which could be assigned to the ortho-and meta-H atoms of the meso-pyridyl groups, respectively, upon coordination to the zinc porphyrin moieties (Figure 2 a).…”

“…[8] When this solution was evaporated to dryness, and the residue was re-dissolved in CCl 4 2 ] was nearly unity (entry 6; se = 2 %). Since the dielectric constants of the regioisomers of xylene are again nearly identical (2.27 and 2.57), the solvatochromic response thus observed suggests that [ZnP( ) 2 ] recognizes the shapes of solvent molecules when it forms the cyclic tetramer.…”

“…In contrast to [{ZnP() 2 , which possess one and four triple bonds in the spacer, respectively, were not solvatochromic in the nonpolar solvents examined (see Figure S4 in the Supporting Information), [6] which indicates that the spacer between the zinc porphyrin units in [ZnP() n ] plays a critical role in the observed solvatochromic response. One of the most important factors in this respect is the p conjugation between the zinc porphyrin units.…”

“…On the other hand, the energy difference between the two conformers of reference [ZnP( ) 4 *] was estimated by means of DFT calculations (B3LYP/6-31G*) to be negligibly small (0.09 kcal mol À1 ; see Figure S5 in the Supporting Information). [6] This small energy difference may be one of the main reasons why [{ZnP() 4 Figure S5 in the Supporting Information) [6,16] is not negligible, it can be expected that [{ k ZnP() 2 . We presume that the balance between these competing factors, that is, the preferences arising from p conjugation and dipole-dipole interaction, may vary depending on the solvents, whilst their dipole moments are equally low.…”