Emission shift of an amphiphilic α-cyanostilbene derivative through concentration-driven two-step assembly with cucurbit[7]uril

In this study, we synthesized an amphiphilic alpha-cyanostilbene derivative (E-form)-1-(12-(2-(2-(benzo[d]thiazol-2-yl)-2-cyanovinyl)-5-(diethylamino)phenoxy)dodecyl)pyridin-1-ium bromide (denoted by BCPB). As being dissolved in aqueous solution, BCPB shows strong emission of excimers at around 660 nm due to the formation of aggregates. Addition of different amount of CB [7] into the solution leads to the emission shift from 660 nm, firstly to 540 nm and then to 588 nm. The emission shift is attributed to the two-step assembly driven by the concentration of CB[7], and the molar ratios of CB[7]/BCPB (denoted by R-m) play a critical role for the shift. As R-m <= 4, CB[7] mainly interacts with the cationic pyridinium group of BCPB to form BCPB@CB[7] complex. As R-m > 4, another CB[7] binds to the diethylamino group at one end of mcyanostilbene to form BCPB@CB[7](2) complex. The two-step assembly well explains the emission shift of BCPB.