Circularly Polarized Luminescence and SHG Chiral Signals of Helical TPE Macrocycles

Main observation and conclusion One pair of new enantiomers of helical tetraphenylethylene (TPE) tetracycle tetradodecylurea, which show aggregation-induced emission (AIE) enhancement effect, were synthesized by attaching four dodecyl chains to a helical TPE tetracycle tetramine through urea linkage. These two TPE helicates bearing long alkyl chains could display strong circular dichroism (CD) and circularly polarized luminescence (CPL) signals not only in solution but also in solid state. Due to strong van der Waals interactions between the alkyl chains, the absolute dissymmetrical factor |g(lum)| was up to 6.6 x 10(-3) , which was 2-3 fold larger than that of the helical TPE tetracycle tetramine (TPETA) without long alkyl chains in solution. Due to bearing hydrophilic urea units and hydrophobic long dodecyl chains, the helical TPE tetracycle could form chiral Langmuir-Blodgett (LB) monolayers at air/water interface and showed a strong and stable second harmonic generation (SHG) chiral signals. The degree of chiral excess (DCE) for P-isomer monolayer was up to -0.682 +/- 0.0014. This is the first example to detect chirality at the air/water interface for chiral AIE molecules. It provides a new access to the application of chiral AIE compounds in nonlinear optical activity.

Automated summary

Two new enantiomers of helical TPE molecules with aggregation-induced emission (AIE) enhancement effect were synthesized, exhibiting strong circular dichroism (CD) and circularly polarized luminescence (CPL) signals in both solution and solid state. The TPE molecules with long alkyl chains showed stable second harmonic generation (SHG) chiral signals at the air/water interface when forming Langmuir-Blodgett (LB) monolayers.