Emerging applications of curved aromatic compounds

In this forum article, we discuss selected recent contributions to the field of nonplanar aromatic molecules, focusing on properties that arise from molecular curvature. Ten reports are highlighted demonstrate diverse applications curved aromatics in materials science would not be achieved by their planar congeners. Graphene is a carbon allotrope comprising single, flat layer hexagonally arranged sp2-hybridized atoms. A similar preference for structure also found large benzenoid hydrocarbons, such as hexa-peri-hexabenzocoronene, which can viewed fragments graphene (nanographenes). Notably, different classes nanographenes have been synthesized using various strategies [1.Majewski M.A. Stępień M. Bowls, hoops, and saddles: synthetic approaches molecules.Angew. Chem. Int. Ed. 2019; 58: 86-116Crossref PubMed Scopus (223) Google Scholar]. particular, incorporation five-membered ring into nanographene commonly used create bowl-like, positively structures [2.Saito et al.Figuration bowl-shaped π-conjugated molecules: functions.Mater. Front. 2018; 2: 635-661Crossref (162) Scholar], whereas seven- or eight-membered typically produces negative curvature saddle-shaped geometries [3.Márquez I.R. al.Synthesis distorted containing carbocycles.Chem. Commun. 54: 6705-6718Crossref Helicene motifs, bear structural relationship negatively nanocarbons, extensively construct chiral with unusual chiroptical features [4.Mori T. Chiroptical symmetric double, triple, multiple helicenes.Chem. Rev. 2021; 121: 2373-2412Crossref (220) Formation closed loops yields neutrally systems, cycloparaphenylenes (CPPs), nanobelts, cyclophanes, many display unique optical host–guest chemistry [5.Guo Q.-H. al.Aromatic hydrocarbon belts.Nat. 13: 402-419Crossref (69) years, these conjugated π-systems received considerable interest because unprecedented optical, redox, charge transport, self-assembly depend type present molecule. highlight some recently reported fields functional dyes, chemical sensors, electroactive materials. each ten examples, was essential achieving desired function. 2022, Li coworkers [6.Li Q.-Q. al.Diazapentabenzocorannulenium: hydrophilic/biophilic cationic buckybowl.Angew. 2022; 61e202112638Google Scholar] fluorescent bioimaging probe featured diazapentabenzocorannulenium cation [1]+ (Figure 1A ). The presence charged heteroatoms were proposed confer solubility polar solvents. Thus, buckybowl could biocompatible fluorescence despite lack hydrophilic substituents. chloride salt [1][Cl] highly dispersible water, showing at 511 nm photoluminescence quantum yield 6%. Confocal imaging showed selectively localize mitochondria after cellular uptake tumor cell types. Such selective subcellular localization reflect membrane potential mitochondria. cyclooctatetraene derivative 2 bearing two phenazine units fused nonadjacent double bonds described 2021 Goto colleagues [7.Goto Y. al.Dynamic polymer free volume monitored single-molecule spectroscopy dual flapping dopant.J. Am. Soc. 143: 14306-14313Crossref (16) 1B). Compound has bent geometry ground state (S0), undergoes planarization when excited lowest singlet (S1), produce emission Stokes shift 4800 cm–1 (λmaxem = 518 nm). viscous media, S1 partially suppressed, yielding signature 460 nm), ratiometric analysis. authors suitable noninvasive measurement dynamic polymers, an important quantity developing chromatographic media. excited-state polystyrene sample occurred only molecule surrounded more than 280 Å3. [4]Cyclo-2,8-chrysenylene 3, Sato 2017 [8.Sato S. al.Chiral intertwined spirals magnetic transition dipole moments dictated cylinder helicity.Proc. Natl. Acad. Sci. U. A. 2017; 114: 13097-13101Crossref (152) represents segment (12,8) single-walled nanotube 1C). Pure enantiomers 3 exceptionally dissymmetry factors circular dichroism circularly polarized luminescence spectra, values high |gabs| 0.167 |glum| 0.152, respectively, recorded (P)-3 443 nm. value, one order magnitude greater those determined earlier metal-free organic molecules. Theoretical calculations predicted electronic (μ) (m) oppositely oriented along axis, thus maximizing rotatory strength R |μ|·|m|·cosθ θ 180°. Besides 0.80 attained compound toluene, thereby fulfilling criteria efficient luminescence-emitting material. An example emerging photovoltaics 2019 Conrad-Burton [9.Conrad-Burton F.S. al.Controlling fission contortion.J. 141: 13143-13147Crossref (40) They contorted perylene diimide (PDI) derivatives 4a 4b introducing terphenyl bridges spanned bay regions PDI core 1D) shown X-ray crystallography possess longitudinally backbone. Density theory (S1) triplet (T1) energies 4 meet energetic requirement fission, is, E(S1) ≥ × E(T1). experimentally undergo time constant τ1 ≈ 2.5 ps, much faster (τ1 180–3800 ps). Host systems π surfaces designed binding appropriately shaped guest spherical guests, fullerenes, accomplished either surfaces, providing access novel charge-transfer systems. use positive exemplified tweezers 5a 5b, consisting azabuckybowls interconnected via carbazole phenanthrene unit, 2018 Takeda 1E) [10.Takeda al.Azabuckybowl-based C60 C70 receptors.J. 140: 6336-6342Crossref (81) Each tweezer bind fullerene (C60 C70) concave–convex interaction association constants (107–108 M−1 toluene). Both exhibited enhanced two-photon absorption cross-sections upon complexation fullerenes. nonlinear originate intermolecular transfer supramolecular donor–acceptor–donor assemblies. porphyrin–[10]CPP conjugate 6, Xu [11.Xu al.A [10]CPP junction enables electron modular porphyrin–[10]CPP⊃fullerene complexes.Angew. 57: 11549-11553Crossref enabled chemically intact fullerenes 1F). cavity hoop-like unit served site 1.6 106 toluene. Upon photoexcitation, complex 6⊃C60 demonstrated form metastable charge-separated 6•+⊃C60•−. This occurrence intra(supra)molecular porphyrin bound evolution absorbances 670 1090 2020, Schaub [12.Schaub T.A. al.Exploration solid-state sorption shape-persistent macrocyclic nanocarbons bulk small aggregates.J. 2020; 142: 8763-8775Crossref (57) spiro[n,n]CPPs 7a (n 8) 7b 10), both adopting lemniscate-like shape 2A ) Sorption small-molecule vapors samples quartz-crystal microbalance measurements explained terms interactions between nanohoops analyte comparison [9]CPP, affinities lemniscates toward benzene its increased 70–100%. superior affinity over [n]CPPs attributed arrangement molecules materials, packed loosely, facilitating operating principle [13.Li C. al.Functionalized stacks hexabenzoperylenes platform biological sensing.Chem. 4: 1416-1426Abstract Full Text PDF (31) who developed field-effect transistor (OFET) sensor functionalized (HBPs, 8a–c; Figure 2B). twisted HBP contains [6]helicene subunits forms one-molecule-thick nanosheets stacking. OFET devices based trimethylsilyloxy-functionalized 8a biotin-functionalized 8b detect fluoride (detection limit 1 μM) streptavidin 36 pM), respectively. choice skeleton crucial π–π interaction-mediated assembly function obstructed sensing substituents, proved 8c. 2021, Furukawa [14.Furukawa al.Ferroelectric columnar assemblies bowl-to-bowl inversion cores.Nat. 12: 768Crossref (33) cores switchable components ferroelectric Their work relied hexaalkoxy-substituted trithiasumanene 9, stacking 2C). Trithiasumanene chosen it possesses moment 1.03 D low barrier (1.9 kcal mol−1). Self-assembled 9 polarization application voltage pulse, followed relaxation macro through bowl bulk. changes provide new switching, fabrication high-density memory Zhang [15.Zhang al.Charging covalent network.J. 5231-5238Crossref (26) network 10 octabenzo[8]circulene (OB8C) lithium ion batteries 2D). carbon-rich anode material lacking long-range order. At current density 100 mA g−1, maximum discharge capacity 830 mAh g−1 (after 66 cycles) Coulombic efficiency exceeded 98% 200 cycles). porosity material, originating OB8C, believed allow diffusion ions barriers. OB8C considered responsible strong ions. As illustrated aforementioned enable range useful functionalities accessible conventional, aromatics. system modulate properties, wavelength, strength, energetics. preferences porous nature solid sensing, responsive, emergence promising areas provides stimulus continued exploration will motivate further developments methodologies required scalable production Financial support National Science Center Poland (UMO-2018/29/B/ST5/01842 M.S.) gratefully acknowledged. No interests declared.