Fluoride Anions: Unexploited but Effective Halogen Bond Acceptors

Daolio, Andrea; Pizzi, Andrea; Nayak, Susanta K.; Dominikowska, Justyna; Terraneo, Giancarlo; Metrangolo, Pierangelo; Resnati, Giuseppe

doi:10.1002/asia.202300520

Cited by 1 publication

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References 39 publications

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“…Until recently, the use of PDIs as chromophoric electron acceptors in OPVs has been marked by inefficiency. , This inefficiency can be attributed to the tendency of PDIs to aggregate into large crystalline domains and to rapidly form excimers when photoexcited that hinder charge separation at interfaces. ,,− To address this issue and enhance the solubility of PDIs while tuning their electronic properties, researchers have turned to fluorination in addition to a broader array of methods involving heteroatom substitution. − This is a consequence of the electronegativity of fluorine and its relatively small van der Waals radius (1.35 Å), which closely resembles that of hydrogen (1.20 Å). Fluorination can circumvent the substantial steric hindrance often caused by other electron-withdrawing groups, thereby minimizing intramolecular torsion.…”

Section: Introductionmentioning

confidence: 99%

Structure-Dependent Triplet State Formation in Fluorinated Perylenediimide Single Crystal Polymorphs

Williams,

Brown,

Palmer

et al. 2024

J. Phys. Chem. C

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Perylenediimide (PDI) and its derivatives have garnered significant attention as promising n-type semiconductors to replace fullerenes as acceptors in organic photovoltaic cells (OPVs). However, the aggregation tendencies and rapid excimer formation of PDIs have hindered their efficiency in OPVs. To address this issue and enhance solubility while fine-tuning their electronic properties, researchers have explored fluorination strategies. In this study, we investigate the structure–function relationship of two crystalline N,N-bis(2′,2′,3′,3′,4′,4′,5′,5′,6′,6′,7′,7′,8′,8′,8′-pentadecafluorooctan-1-yl)perylene(3,4:9,10)bis(dicarboximide) (FPDI) polymorphs, namely, FPDI-α and FPDI-β. Their crystal structures show that the π systems of the FPDI molecules in FPDI-α adopt an orthogonal geometry, while those in FPDI-β are parallel and slip-stacked. We report their excited state dynamics using transient absorption and fluorescence microscopy and time-resolved electron paramagnetic resonance spectroscopy. Upon photoexcitation, both crystal polymorphs exhibit the formation of a lowest excited singlet (S1) state with substantial charge transfer (CT) character. This S1-CT state in FPDI-α decays in τ = 350 ps to form the FPDI triplet state via spin–orbit charge-transfer intersystem crossing in near-quantitative yield, while the S1-CT state in FPDI-β decays back to the ground state in τ = 140 ps. This study illustrates the influence of different packing motifs on photoinduced intermolecular CT processes in single crystals of the same molecule and contributes to an understanding of the role of fluorination in optimizing PDI-based molecular materials for CT state formation in the solid state.

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