Imide-Functionalized Helical PAHs: A Step towards New Chiral Functional Materials

Abstract

Attachment of cyclic imide groups to polycyclic aromatic hydrocarbons (PAHs) leads to fascinating electronic and luminescence properties, the rylene diimides being the representative example. The close to unity fluorescence quantum yields and electron acceptor properties render them suitable for application in organic electronics and photovoltaics. The recent reports show that in line with planar PAHs, the imide functionalization has also endowed helical three-dimensional PAHs with similar beneficial photophysical properties. In this article, we have summarized the state-of-the-art research developments in the field of helicene-imide hybrid functional molecules, with a particular focus on synthesis, (chir)optical and redox properties, and applications in electronics. Additionally, we have highlighted our recent work, introducing a novel family of functional chiral molecules, namely, [n]helicene diimides the three-dimensional relatives of rylene diimides.

New advances in chiral nanographene chemistry

“…Combining the properties of imides with the chiroptical properties of chiral molecules provides exciting opportunities for unique behavior and applications. Early strides in this field were made by the Würthner 69,70 and Müllen 71 groups, and recently this class of structure has been thoroughly reviewed by Ravat and Saal, 72 and Yin, Guan, and coworkers. 73 Here we will highlight a few notable works.…”

Pyrene bridged double[7]helicene embedded with a heptagonal ring

“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24] Moreover during the last few years multiple [n]helicene-embedded nanographenes with numerous aromatic cores have been developed. 23,[25][26][27][28][29][30] Preserving their core properties, multi[n]helicene showed unique characteristics due to an increased π-conjugation and molecular packing. 23,[31][32][33][34][35][36] Although these molecules provided an opportunity for synthetic chemists to explore the limits of aromaticity and π-bonding by designing extremely twisted PAHs, [37][38][39][40][41][42] often the key challenge remained with the configurational stability and isolation of enantiopure [n]helicene derivatives as well as their stereoselective synthesis.…”

Push–pull [7]helicene diimide: excited-state charge transfer and solvatochromic circularly polarised luminescence

“…In the pursuit of chiral functional molecules featuring favourable electronic and optical characteristics, coupled with robust thermal and chemical stability, incorporating imide functionalities onto an aromatic scaffold has emerged as a successful strategy. [1][2][3][4][5][6][7][8] Notable attention has been directed towards exploring the functional properties of chiral imide-containing helicenes. [9][10][11][12][13][14][15][16] Recently we reported a new family of helically chiral diimides, namely, [n]helicene diimides ([n]HDIs, n = 5, 6, and 7).…”

“…This observation can be explained by the fact that the maxima of the luminescence dissymmetry factor (g lum ) values lie towards the higher-energy edge of the emission spectra, with values on the order of B0.45 Â 10 À2 in aprotic solvents (Table 1). While the g lum value of 2 is higher than 1 ([7]HDI-OMe) and [5]HDI-OMe, it is decreased compared to [6]HDI-OMe (Fig. S2, ESI †).…”