Scholl reaction of hexaphenylbenzenes with hexakis-alkoxy substituents

ABSTRACT

The hexakis-alkoxy substituted hexa-peri-hexabenzocoronene (HBC) discotic core is desirable aiming at strong π–π interactions in columns, electronic tuning of the core and better processability. The feasibility of synthesising a new hexakis-alkoxy substituted HBC core is investigated and described in this report. Experimentally, it has been found that when two alkoxy substituents in a peripheral aromatic ring are placed meta to each other, the Scholl reaction results in fully cyclised HBC product. Surprisingly, when the alkoxy groups are ortho to each other, cyclodehydrogenation results in the formation of a partially fused product. This partially-fused ring formation happens under varying reaction conditions and irrespective of the differing alkyl chain lengths. Most plausibly, the considerable strain in the fully fused molecule from 1,2 isomer is the reason to cease the reaction at the partially fused stage. Further quantum-mechanical calculations at the B3LYP/6-31G(d) level of theory also support the hypothesis. The incorporation of two electron donating groups has also reduced the band gap compared to its mono alkoxy analogue. Reduced band gap values are promising feature of these molecules for finding future applications of discotic liquid crystals in organic electronics.

Graphical Abstract

KEYWORDS:

• Hexabenzocoronene
• alkoxy
• Scholl reaction
• hexaphenylbenzene
• liquid crystals

Acknowledgments

SKP is grateful for the financial support from CSIR bearing Sanction No. 02(0311)/17/EMR-II for the project entitled “Synthesis and Characterisation of Nanographenes based on hexabenzocoronene Discotics for Photovoltaics Applications”. We are grateful to NMR and HRMS research facility at IISER Mohali for recording NMR and mass spectrum, respectively. SS acknowledges the receipt of a graduate fellowship from CSIR-NET. DA gratefully acknowledges computational facility at Indiana University, Bloomington, IN, USA. DA also thanks SERB (DST), India for Early Career Award (ECR/2017/001764).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Council of Scientific and Industrial Research [grant number 02(0311)/17/EMR-II] and SERB (DST), India for Early CareerAward (ECR/2017/001764).