Solvent-induced chirality inversion involving supramolecular helix transformation and color-tunable fluorescence of a C_6-symmetric hexakis(phenylethynyl)benzene derivative

摘要

A C_6-symmetric disk-like molecule, a hexakis(phenylethynyl)benzene derivative bearing chiral a1anine parts, L-1, exhibited a solvent-induced supramolecu1ar helix-sense inversion involving conformational changes followed by destruction of the supramolecu1ar helical column. This phenomenon has been found by investigating the supramolecu1ar assembly state of L-1 in mixed solvents of various chloroform (CHCl_3)-hexane (Hx) ratios. L-1 forms a stable helical columnar assembly via multiple noncovalent bonding interactions in nonpo1ar Hx, while the molecules in re1atively po1ar CHCl_3 are in a molecu1arly dispersed state. Although one would expect disruption of the helical column with the addition of nonhelicogenx CHCl_3, an opposite-handed helical columnar structure was formed at 8-15 vol% of CHCl_3, and subsequently the inverted helical column was disassembled by a further increase of CHCl_3. In addition, this morphological transformation was accompanied by a significant change in fluorescent color, which varies over a wide visible range from orange in an original helical columnar state to light blue in a molecu1arly dispersed state through yellow in an inverted helical columnar state. These unprecedented behaviors are shown by the spectroscopic results, and the molecu1ar conformations of L-1 and the driving force for the helical sense inversion are discussed.