Tunable Photochemical/Redox Properties of (Phenylthio)_ncorannulenes: Application to a Photovoltaic Device

Abstract

The additive substituent effect of phenylmercapto derivatives of corannulene are investigated by spectroscopic, electrochemical, and computational techniques. The per-substituted phenylmercaptocorannulene is incorporated as a replacement for [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) in a photovoltaic device. Keywords: photovoltaic, electrochemistry, corannulene, photochemistry IntroductionIn a similar fashion to fullerenes, 1 curved aromatic hydrocarbons, like corannulene, 1, behave as electrondeficient π-systems, 2 the redox properties of which can be tuned by derivatization (Figure 1). 3 Curved aromatic hydrocarbons related to corannulene have been used in various materials applications including the development of fluorescent chemosensors, 4 organic field-effect transistors, 5 and heterojunction photovoltaics. 6 In each case, specific photochemical and redox properties have been important to the success of the application. Tuning the photochemical and redox properties of corannulene cognates corresponds to influencing the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels as well as the HOMO-LUMO gap. Whereas simple alkyl substituents raise HOMO and LUMO levels, 7 fluorinated alkyl groups lower both; 8 in neither case is there a substantial effect on the HOMO-LUMO gap as gauged from absorption spectroscopy. Organothio-substituents raise HOMO and lower LUMO levels such that one can obtain good electron acceptors with smaller HOMO-LUMO gaps. For example, compared to 1, a pale yellow material with first reduction at −2.33 eV in acetonitrile, decasubstitution of 1 with thiophenol (SPh) produces a deep red material with the first reduction potential at −1.22 eV, 10 which is similar to the reported value of −1.17 volts for [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM). Given that many high-performing organic photovoltaic (OPV) devices rely on C 60 and its derivatives to act as electron acceptors, 11 this similarity in electrochemistry between PCBM and decakisphenylmercaptocorannulene motivates a study into the nature of tuning the physical properties (electrochemistry, ultraviolet-visible (UV-Vis) absorption, fluorescence, and phosphorescence) of corannulene by phenylmercapto substitution and the photovoltaic characterization of decakis(phenylthio-)corannulene as an acceptor in an OPV device. Furthermore, the optoelectronic tunability of corannulenes makes them potentially useful as organic light emitting diodes (OLEDs), 12 as organic conductors, 13 or in high density carbon electrodes. Vol. 27, No. 10, 2016 ExperimentalGeneral synthesis 1,3-Dimethyl-2-imidazolidinone (DMI; 5-10 mL, dried over molecular sieve) was added to a round bottom flask equipped with a reflux condenser. Thiophenol (1.5 equiv./ reaction site) and sodium hydride (1.2 equiv./reaction site, 60% in mineral oil) were added and stirred at room temperature for 10 min. The halogenated corannulene derivative (2a-7a, 1 equiv.) was added and the solution was heated at 60 °C for 18 h. The...

Ferrocenes with a Persulfurated Cyclopentadienyl Ring: Synthesis, Structural Studies, and Optoelectronic Properties

“…The so‐called “optical band gap”, defined either from the long‐wave absorption maxima or from the onsets of these bands, can thus be calculated as 2.82–2.84 or 2.37–2.38 eV, respectively. This lack of sensitivity towards substituent effects is in sharp contrast to the above‐mentioned observation with metal‐free persulfurated arenes, but confirms the old observation for ferrocenes that this band is “relatively insensitive to substitution on the ring” . Also not very astonishing, both compounds showed neither fluorescence nor phosphorescence.…”

“…The interesting electronic properties shared by this compound class are mainly due to the fact that “phenylthio substituents attached to aromatic cores result in a reduction of the HOMO–LUMO gap”, “primarily due to LUMO stabilization” . Upon addition of SPh groups a bathochromic shift of the longest wavelength absorption by 10–15 nm is observed together with an increase of the reduction potential by 0.1 V …”

Decakis(arylthio)corannulenes: Transferable Photochemical and Redox Parameters and Photovoltaic Device Performance

“…Perchlorination of 1 by BMC conditions, affords tetradecachlorocorannulene that can be rearomatized by refluxing in diphenyl ether to give decachlorocorannulene 2 . Synthesis of 3g uses 2 and thiophenoxide with sodium hydride as base in a polar solvent such as dimethylimidazolone (DMI) at 60 °C for 24 h ,. [7a] This general method, by varying the thiophenoxide, readily allowed the preparation of the series 3a – f ( 3e in ortho ‐dichlorobenzene at 160 °C).…”

“…In the case of 1 , which can bear ten such substituents, the longest‐wavelength UV/Vis absorption changes from about 290 nm in 1 to 420 nm in decakis(phenylthio)corannulene 3g , a change in the optical gap of 130 nm . Electrochemically, the redox gap from first oxidation to first reduction potential is 3.6 eV for 1 vs. 2.0 eV for 3g , a change in redox gap of 1.6 eV. Focusing just on the reduction potential of 1 and 3g , which relates to the electron affinity, the change is nearly 1.0 eV (–2.45 eV vs. –1.5 eV, respectively).…”

An S10-Symmetric 5-Fold Interlocked [2]Catenane

“…Corannulene was chosen as a suitable 5-fold-symmetric scaffold , because of its potential for functionalization via a variety of synthetic routes and its curved aromatic surface, which may enhance the guest binding properties of assemblies via aromatic stacking interactions Figure ) was synthesized by nucleophilic aromatic substitution from sym -pentachlorocorannulene and 4-aminothiophenol in 1,2-dimethylimidazolone in the presence of sodium hydride (Scheme S1).…”