Details

Autor(en) / Beteiligte

• Buchta, Michal
• Rybáček, Jiří
• Jančařík, Andrej
• Kudale, Amit A.
• Buděšínský, Miloš
• Chocholoušová, Jana Vacek
• Vacek, Jaroslav
• Bednárová, Lucie
• Císařová, Ivana
• Bodwell, Graham J.
• Starý, Ivo
• Stará, Irena G.

Titel

Chimerical Pyrene-Based [7]Helicenes as Twisted Polycondensed Aromatics

Ist Teil von

• Chemistry : a European journal, 2015-06, Vol.21 (24), p.8910-8917

Ort / Verlag

Weinheim: WILEY-VCH Verlag

Erscheinungsjahr

2015

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• Chimerical pyrene‐based dibenzo[7]helicene rac‐1 and 2H‐pyran[7]helicene (M,R,R)‐(−)‐2, in which two pyrene subunits are fused to the [7]helicene/[7]heterohelicene scaffold, were synthesised by means of Ni0‐ or CoI‐mediated [2+2+2] cycloisomerisation of dipyrenyl‐acetylene‐derived triynes. Pyrene‐based dibenzo[7]helicene 1 was obtained in enantioenriched form by enantioselective cycloisomerisation under Ni0/QUINAP catalysis (57 % ee) or in enantiopure form by racemate resolution by liquid chromatography on a chiral column. 1,3‐Allylic‐type strain‐controlled diastereoselective cycloisomerisation was employed in the synthesis of enantiopure (M,R,R)‐(−)‐2. Physicochemical properties of 1 and 2 encompassing the helicity assignment, stability to racemisation, X‐ray crystal structure, UV/Vis, experimental/calculated electronic circular dichroism and fluorescence spectra were studied. Accordingly, comparison of the X‐ray crystal structure of (M,R,R)‐(−)‐2 with calculated structures (DFT: B3LYP/cc‐pVDZ, B97D/cc‐pVDZ) indicated that its helical backbone is slightly over‐flattened owing to intramolecular dispersion forces between tert‐butylated pyrene subunits. Both 1 and 2 are fluorescent (with quantum yields in dichloromethane of ΦF=0.10 and 0.17, respectively) and are suggested to form intramolecular excimer states upon excitation, which are remarkably stabilised and exhibit large Stokes shifts (296 and 203 nm, respectively). Do the twist: Two pyrene units can be incorporated into dibenzo‐ or 2H‐pyran[7] helicene scaffolds to form a new class of twisted polycondensed aromatics (see figure). A key process employed in their synthesis is Ni0‐ or CoI‐mediated [2+2+2] cycloisomerisation of dipyrenyl triynes. The chimerical pyrene‐based [7]helicenes could be obtained in enantiopure form through racemate resolution or asymmetric synthesis. Their physicochemical properties have been studied.