Synthesis and Properties of [7]Helicene-like Compounds Fused with a Fluorene Unit

Abstract

[7]Helicene-like compounds with a fluorene unit were successfully synthesized using a platinum-catalyzed double cyclization reaction. Crystal structures and photophysical properties of these compounds were also studied. In particular, they were found to exhibit a high fluorescence quantum yield and a relatively large g value (dissymmetric factor) of circularly polarized luminescence (CPL) for small molecules.

Azabora[5]helicene Charge‐Transfer Dyes Show Efficient and Spectrally Variable Circularly Polarized Luminescence

“…Potential applications are chiral sensing or the preparation of chiroptical systems with innovative photophysical design . Helicenes belong to the most frequently reported CPL‐SOM architectures, among them carbo[ n ]helicenes, helicenes that incorporate heteroatoms (azahelicenes, oxahelicenes, thiahelicenes), and metallahelicenes …”

Phosphorescence Resulting from Interaction between Two Non‐equivalent Metals on a Helical π‐Conjugated Surface

“…The excitation spectrum at 650 nm of complex 3 corresponds to the absorption spectrumof3,w hich suggeststhat the emission comes from complex 3 itself. Note that the ligand precursor LH also showedp hosphorescencea t6 00 nm (See SI), [15] which can be clearly distinguished from that of 3 at 650 nm.…”

Synthesis of Optically Pure Helicene Metallocenes

“…Ther eaction of deprotonated rac-LH with 0.5 equivalent of RuCl 2 (dmso) 4 afforded bis-helicene ruthenocene 2 as am ixture of (P,P)and (M,M)-2 (rac-2), and (P,M)-2 (meso-2)i na7:3r atio,i n 26 %total yield. In comparison to LH, [6] each complex exhibited shorter C1 À C2 and C3 À C4 bonds,a nd al onger C2 À C3 bond, suggesting that the cyclopentadiene moiety of LH was aromatized to aCpanion. Enantiopure (P)-LH obtained by separation of ar acemic mixture using chiralphase HPLC was converted into optically pure monohelicene ruthenocene (P)-1.O ptically pure bis-helicene ruthenocene (P,P)-2 was synthesized from (P)-LH, without generation of meso-2.T he opposite enantiomers,( M)-1 and (M,M)-2,w ere also prepared from (M)-LH.…”

“…In 2007, Thiel et al made great contributions in the synthesis of as eries of metal complexes with dibenzo[c,g]fluorenyl (Dbf) ligand ( Figure 2b). [6] Ther acemization barrier was high enough so that we could isolate both enantiomers of LH by chiral-phase HPLC separation. [5a] Recently,w er eported the synthesis of rac-9H-cyclopenta[1,2-c:4,3-c']diphenanthrene (LH), which has ar igid helical shape comprised of seven fused rings (Scheme 1).…”