2,15-dibutoxy-6,11-dicyano[6]Helicene: Synthesis, electrochemical, photophysical properties and computational studies

Abstract

2,15-Dibutoxy-6,11-dicyano[6]Helicene (CN-HEL) has been prepared through a two-step sequence under mild conditions, in an overall 78% yield, starting from 2,7-bis(cyanomethyl)naphthalene as a suitable material. The Helicene has been experimentally characterized and its absorption and photoluminescence (PL) properties have been evaluated showing a blue emission in the visible spectrum. A strong absorption is entirely in the UV region (λmax = 290 nm), yet fluorescence occurs at 400 nm. This equates to a Stokes shift of 1.17 eV (9482 cm−1) which is among the largest Stokes shifts reported for small molecules, making it a promising candidate for optoelectronic applications. Furthermore, the 1H NMR, FT-IR, UV-vis and PL spectra were computed by means of the very efficient time-dependent density functional theory (TD-DFT) approach. The computed spectra with two recommended density functional (PBEPBE and cam/B3LYP) and extended basis sets compare very well with the corresponding experimental data. HOMO and LUMO energy levels were also investigated experimentally, showing an electrochemical band gap of 2.54 eV. Results obtained throughout this work are of great importance and prove the relevance of the target Helicene to be used in a wide range of both existing and new applications such as fluorescence probes and molecular sensors.