Tetrasubstituted Peropyrenes Formed by Reductive Aromatization: Synthesis, Functionalization and Characterization

Abstract

The chromophore class of 1,3,8,10-tetrasubstituted peropyrenes was effectively synthesized from peropyrenequinone via a Zn-mediated reductive aromatization approach. In one step, a symmetric functionalization of the peropyrene backbone introducing silylethers (2,3), pivaloyl (4), triflyl (5) and also phosphinite ( 6) groups was established. Furthermore, the potential of using 4 and 5 in transition metal catalysed cross couplings was explored leading to 1,3,8,10tetraaryl (8-11) and tetraalkynyl ( 7) peropyrenes. The influence of various substituents on the optoelectronic properties of these π-system extended peropyrenes was investigated in solid state by means of X-ray crystallography, in solution by means of UV-Vis and fluorescence spectroscopy and by their redox properties studied via cyclic voltammetry. By comparison with DFT and TD-DFT calculations, it could be elucidated that introduction of a broad variety of substituents in such versatile one or two step procedures leads to peropyrenes with easily tunable HOMO and LUMO energies ranging in a gap window of 0.8 eV. The frontier molecular orbital energies identify the target molecules as promising candidates for hole transporting semiconductors.

2,9‐Diazadibenzoperylene and 2,9‐Dimethyldibenzoperylene‐1,3,8,10‐tetratriflates: Key to Functionalized 2,9‐Diazaperopyrenes

“…As expected sp 2 nitrogen atoms in the 2,9-position lead to a stabilization of the frontier orbitals. The same trend was reported for similar tetrasubstituted peropyrenes [27] and related 2,8-diazaperylenes, recently. [37]…”

“…Starting material 1 b was synthesized via an oxidative coupling of 2-methyl 3-hydroxy-1-phenalenone in a potassium hydroxide melt [17] modifying similar oxidative reactions. [27,33] This oxidative coupling followed by reductive triflylation protocol allowed the introduction of other organic groups in 2,9-and 1,3,8,10-position of peropyrenes. [27] Orange solid 2 a can be handled under aerobic atmosphere, however in solution and in presence of air and moisture, 2 a is re-oxidized to starting material PTCDI, which is deposited as thin film on the inner glass surface of the flask, as is verified by IR spectroscopy (Figure S1).…”

“…[27,33] This oxidative coupling followed by reductive triflylation protocol allowed the introduction of other organic groups in 2,9-and 1,3,8,10-position of peropyrenes. [27] Orange solid 2 a can be handled under aerobic atmosphere, however in solution and in presence of air and moisture, 2 a is re-oxidized to starting material PTCDI, which is deposited as thin film on the inner glass surface of the flask, as is verified by IR spectroscopy (Figure S1). This selective aerobic reoxidation and deposition reaction can be used to fabricate pure and transparent PTCDI films from solution.…”

“…In this report we focus on the synthesis of DDPs, the functionalized DBP series is reported separately. [27] Three representative examples of functionalization reactions for DDP 3 a are shown in Scheme 3. Firstly, Suzuki-Miyaura cross-coupling reactions were carried out using phenyl boronic acids (1.5 instead of 4.0 eq per functional group) and catalytic amounts of Pd-(PPh 3 ) 4 (2.5 mol % per functional group) to obtain 1,3,8,10tetraaryl DDPs 5 a-5 e. The yield for 5 b is similar to previously reported applying tetrapivaloates with fourfold excess of boronic acid per functionality.…”

“…Recently we described a novel synthetic approach to DDPs and DBPs. [17,27] Our method comprises a reductive functionalization at the carbonyl positions of one of the most prominent organic dyes in photo chemistry and physics, perylenetetracarboxylic diimide (PTCDI) and the introduction of four replaceable and versatile triflate substituents. We also demonstrated a reductive silylation and functionalization approach of peropyrenes higher homologues terropyrene and quarterropyrene.…”