Synthesis, Crystal Structure and Photophysical Properties of Pyrene–Helicene Hybrids

Abstract

Synthesis of helically chiral aromatics resulting from fusion of pyrene and [4]- or [5]helicene has been accomplished using photoredox catalysis employing a Cu-based sensitizer as the key step. Photocyclisation experiments for the synthesis of the target compounds were carried out in batch and using continuous flow strategies. The solid-state structures, UV/Vis absorption spectra and fluorescence spectra of the pyrene-helicene hybrids were investigated and compared to that of the parent [5]helicene to discern the effects of merging a pyrene moiety within a helicene skeleton. The studies demonstrated that pyrene-helicene hybrids adopt co-planar or stacked arrangements in the solid state, in contrast to the solid-state structure of the parent [5]helicene. The UV/Vis and fluorescence spectra of the pyrene-helicene hybrids exhibited strong red-shifts when compared to the parent [5]helicene. DFT calculations suggest that the strategy of extending the π surface in the y axis of the helicenes increased their HOMO levels while also decreasing their LUMO levels, resulting in significantly reduced band gaps.

Azahelicenes from the Oxidative Photocyclization of Boron Hydroxamate Complexes

“…[12,13] For that purpose, af low photoreactorw as set up accordingt ol iterature procedures: [14] fluorinated ethylene propylene tubing (FEP;o uter/ inner diameter = 3mm/2 mm) was tightly wrapped around aP yrex water-cooling jacket of ah igh-pressureH gl amp (for details, see the Supporting Information;F igure S1), and the irradiation area of the FEP tubing was covered with two layers of aluminum foil in order to maximize the use of UV light. [12,13] For that purpose, af low photoreactorw as set up accordingt ol iterature procedures: [14] fluorinated ethylene propylene tubing (FEP;o uter/ inner diameter = 3mm/2 mm) was tightly wrapped around aP yrex water-cooling jacket of ah igh-pressureH gl amp (for details, see the Supporting Information;F igure S1), and the irradiation area of the FEP tubing was covered with two layers of aluminum foil in order to maximize the use of UV light.…”

“…In order to shorten the irradiationt ime and suppress any potentiald ecomposition owing to overexposure to UV light, we subsequently performed the photochemical transformation of 8 using ac ontinuous flow strategy. [12,13] For that purpose, af low photoreactorw as set up accordingt ol iterature procedures: [14] fluorinated ethylene propylene tubing (FEP;o uter/ inner diameter = 3mm/2 mm) was tightly wrapped around aP yrex water-cooling jacket of ah igh-pressureH gl amp (for details, see the Supporting Information;F igure S1), and the irradiation area of the FEP tubing was covered with two layers of aluminum foil in order to maximize the use of UV light. Optimizing the reaction conditions ([8] = 0.80 mm,f low rate = 0.37 mL min À1 ,a tmospheric conditions) furnished aza[6]helicene 2b,c ontaining an amide moiety,i n1 6% yield.…”

Synthesis, Structure and Photophysical Properties of Pyrene–based [5]Helicenes: an Experimental and Theoretical Study

“…More interestingly, the distortion angle of [5]helicenes (measured using the terminal aromatic rings) exhibit significant differences, and in the crystal of 7b , a distortion angle of 48.75° was observed, which is in good agreement with the distortion angle of 48.91° as found in the DFT energy minimized model. Meanwhile, the distortion angles of the pyrene‐based [5]helicenes and the parent helicene are summarized (Figure S2), and differences of approximately 10° are observed, which could be attributed to the steric hindrance of the substituents of the terminal aromatic rings.…”

Synthesis of a Helical Bilayer Nanographene

“…[31] As such, we sought to combine all of these aspects into a new molecular system which could be considered a folded, chiral, bilayer nanographene. To maintain conjugation throughout the system and also provide a new entry into the emerging field of chiral nanographenes and p-extended helicenes [32][33][34][35][36] we chose helicene as the chiral PAH linker between HBC layers. The resulting target molecule is an unprecedented helical bilayer nanographene (HBNG).…”