Publication details
Preparation and Physicochemical Properties of [6]Helicenes Fluorinated at Terminal Rings
| Authors | |
|---|---|
| Year of publication | 2019 |
| Type | Article in Periodical |
| Magazine / Source | Journal of Organic Chemistry |
| MU Faculty or unit | |
| Citation | |
| web | Full Text |
| Doi | http://dx.doi.org/10.1021/acs.joc.8b02870 |
| Keywords | HELICAL MOLECULES; CRYSTAL PACKING; RESOLUTION; PHOTOCYCLIZATION; HELICENES |
| Description | The first racemization-stable helicene derivatives fluorinated at terminal rings, 1,2,3,4-tetrafluoro[6]helicene (6) and 1,2,3,4,13,14,15,16-octafluoro[6]helicene (15), were synthesized via the Wittig reaction followed by oxidative photocyclization in an overall yield of 41% of 6 and 76% of 15. The changed electronic structure in fluorinated helicenes was reflected in a slight shift of UV-vis absorption, fluorescence excitation, and emission spectra maxima when compared to unsubstituted [6]helicene. Cyclic voltammetry revealed a moderate decrease in the HOMO-LUMO gap with increasing fluorination. The specific rotation of tetrafluoro[6]helicene 6 enantiomers was found to be approximately 25% lower than that, of unsubstituted [6]helicene. The theoretical study of the racemization barrier suggested a reasonable shift toward higher energy with increasing fluorination. The increasing fluorination also significantly affected the intermolecular interactions in the crystal lattice. The observed CH center dot center dot center dot F interactions led to the formation of 1D-molecular chains in the crystal structures of both fluorinated helicenes. |