Achieving Enhanced Photochromic Properties of Diarylethene through Host-Guest Interaction in Aqueous Solution

Diarylethene (DTE) has been widely used in fluorescence probes, molecular logic gates, optical data-storage devices owing to the excellent photochromic property, while constructing high-performance photochromic DTE in aqueous media remains a big challenge. Herein we present several host-guest systems formed between cucurbit[n]uril (CB[n], n=7, 8, 10) and two water-soluble DTE derivatives 1 and 2 . It was found that host-guest interactions not only affect the photophysical properties of photochromic guests, but also make great differences on the photoreaction process. Different host-guest binding behaviors also lead to different effects on the photochromic properties of guests. In the presence of CB[n], both 1 and 2 showed enhanced emission and higher fluorescence quenching ratio at photostationary state. Besides, CB[10] ⋅1 exhibited faster response rate in cyclization reaction and better photofatigue resistance than free 1 in aqueous solution, while the supramolecular assembly of (CB[8])_n ⋅ ( 2 )_n showed slower response rate in both directions of the reversible photoreaction. Besides, the photofatigue resistance of 2 can be greatly improved through binding with CB[7]. Our results suggest that host-guest interactions could be an efficient way to improve photochromic properties of DTE in aqueous solution.     

Evidence for Kinetic Nucleation in Helical Nanofiber Formation Directed by Chiral Solvent for a Perylene Bisimide Organogelator

The self‐assembly behavior of an achiral perylene bisimide (PBI) organogelator that bears two 3,4,5‐tridodecyloxybenzoylaminoethyl substituents at the imide positions has been investigated in chiral solvents (R)‐ and (S)‐limonene in great detail by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). CD spectroscopic studies on dilute solutions revealed a preferential population of one‐handed helical assemblies in chiral solvent with an enantiomeric excess close to 100 %, whereas AFM images of more than 100 nanofibers of the organogel obtained from more concentrated solutions were found to consist of both handed helices with an enantiomeric excess of only 20 %. This discrepancy is attributed to the fast gelation process at high dye concentration that evidently proceeds through non‐equilibrated nuclei in a kinetic rather than thermodynamic self‐assembly process. Under these conditions the chiral induction from the homochiral solvent may not be adequate in effectively populating only one‐handed helices.