Highly Strained, Radially π-Conjugated Porphyrinylene Nanohoops

Abstract

Small π-conjugated nanohoops are difficult to prepare, but offer an excellent platform for studying the interplay between strain and optoelectronic properties and increasingly, these shape-persistent macrocycles find uses in host-guest chemistry and self-assembly. We report the synthesis of a new family of radially π-conjugated porphyrinylene/phenylene nanohoops. The strain energy in the smallest nanohoop [2]CPT is approximately 54 kcal mol -1 , which results in a narrowed HOMO-LUMO gap and a red shift in the visible part of the absorption spectrum. Due to its high degree of preorganization and a diameter of ca. 13 Å, [2]CPT was found to accommodate C60 with a binding affinity exceeding 10 8 M -1 despite the fullerene not fully entering the cavity of the host (X-Ray crystallography). Moreover, the π-extended nanohoops [2]CPTN , [3]CPTN and [3]CPTA (N for 1,4-naphthyl; A for 9,10anthracenyl) have been prepared using the same strategy, and [2]CPTN has been shown to bind C70 five times more strongly than [2]CPT. Our failed synthesis of [2]CPTA highlights a limitation of the experimental approach most commonly used to prepare strained nanohoops, because in this particular case the sum of aromatization energies no longer outweighs the buildup of ring strain in the final reaction step (DFT calculations). These results indicate that forcing ring strain onto organic semiconductors is a viable strategy to fundamentally influence both optoelectronic and supramolecular properties.

Conjugated Nanohoops Incorporating Donor, Acceptor, Hetero‐ or Polycyclic Aromatics

“…[3]35 [82] 409 2. 4 [83] 442 2.7 10 5 0.34, 0.60 À1.69, À1.92 ---[3]38 [83] 430 4.0 10 5 0.44, 0.73 À1.79, À2.04 ---[3]39 [83] 428 6. [82] [n]36, [86] and…”

“…[n]37-[3]39. [83] Angewandte Chemie Aufsätze 15888 www.angewandte.de nanohoops can be found in Table S1 in the Supporting Information.…”

Supramolekulare Bindungstaschen in [n]Cyclo‐2,7‐pyrenylenen

“…Infolgedessen wurden verschiedene Bottom‐up‐Strategien für die Synthese von CPPs oder deren Derivaten mit Hetero‐ und polycyclischen Aromaten entwickelt [8–12] . Die Einbindung solcher Fragmente ermöglicht Untersuchungen neuer Funktionalitäten und optoelektronischer Eigenschaften dieser makrozyklischen Substanzklasse [13–17] . Zudem konnten durch diese methodischen Arbeiten neue geometrische Formen vom Makrozyklus bis hin zum molekularen Käfig erschlossen werden [18–21] .…”

Supramolecular Assemblies for Electronic Materials

“…The macrocycle component has an alternating diphenyl‐PDI ( P ) and bithiophene ( B ) structure, PBPB (Figure ) . PBPB possesses several characteristics that make it an ideal material to bind to fullerenes . It possesses a large, curved nanospace interior, which is lined with Lewis basic sulfur atoms available for lone pair (n)–π interactions .…”

“…[12] PBPB possesses severalc haracteristics that make it an ideal materialt ob ind to fullerenes. [18][19][20][21][22][23][24][25][26] It possesses a large,c urved nanospace interior, [18,22,24,27,28] which is lined with Lewis basic sulfur atoms available for lone pair (n)-p interactions. [29] We therebyi nvestigate the supramolecular chemistry of PBPB and find it binds av ariety of fullerenes with large association constants( K a ), of up to 9278 m À1 .D espite both components being categorised as n-type materials with similar LUMO levels molecular recognition is concomitant with significant intermoleculare lectronic communication between the two components.…”