Experimental and DFT Studies of the Electron‐Withdrawing Ability of Perfluoroalkyl (R_F) Groups: Electron Affinities of PAH(R_F)_n Increase Significantly with Increasing R_F Chain Length

Abstract

Two series of aromatic compounds with perfluoroalkyl (R ) groups of increasing length, 1,3,5,7-naphthalene(R ) and 1,3,5,7,9-corannulene(R ) , have been prepared and their electronic properties studied by low-temperature photoelectron spectroscopy (PES) (for gas-phase electron affinity measurements). These and many related compounds were also studied by DFT calculations. The data demonstrate unambiguously that the electron-withdrawing ability of R substituents increases significantly and uniformly from CF to C F to n-C F to n-C F .

PAH/PAH(CF3)n Donor/Acceptor Charge‐Transfer Complexes in Solution and in Solid‐State Co‐Crystals

“…The lower part of Figure is a plot of experimental E 1/2 (0/−) values for PAH compounds measured at CSU using the same solvent, electrolyte salt, electrode array, electrochemical internal standard, and potentiostat versus experimental PAH EA s from the literature and PAH(CF 3 ) n EA s measured with the same LT‐PES instrumentation at Pacific Northwest National Laboratory. There are 38 data points in the plot, 10 for PAHs and 28 for PAH(CF 3 ) n compounds with n= 2–6 (most of the individual values are listed in Tables S5 and S6). The ranges of E 1/2 (0/−) values and EA s are 2.64 V and 3.58 eV, respectively.…”

“…Equimolar solutions of various PAH/PAH(CF 3 ) n combinations were drop‐cast onto quartz microscope slides in order to record solid‐state thin‐film UV/Vis spectra. The adiabatic electron affinity ( EA ) of ANTH‐6‐2 was determined at Pacific Northwest National Laboratory as previously described, using a low temperature (10–12 K) apparatus that couples an electrospray ionization source and a temperature‐controlled ion trap to a magnetic‐bottle time‐of‐flight photoelectron spectrometer previously described in detail…”

“…Fluorination, even partial fluorination, can also increase PAH electron affinities, improve air stability, affect PAH charge mobility and photophysics, convert p‐type into n‐type semiconductors (e.g., perfluoropentacene), and convert PAH herringbone structures (e.g., anthracene (ANTH)) into π‐stacked structures (e.g., 1,2,3,4‐ANTH(F) 4 ) . However, CF 3 is a much stronger electron‐withdrawing group (EWG) than F . For example, the DFT‐predicted EA s of perfluoroanthracene (ANTH(F) 10 ) and ANTH(CF 3 ) 10 are 1.84 and 4.01 eV, respectively.…”

“…We have studied the synthesis and physicochemical properties of 53 PAH(CF 3 ) n derivatives prepared by substituting H atoms in twelve unsubstituted PAHs using CF 3 radicals generated from CF 3 I at high temperature ( n= 1–8) . In addition to their spectroscopic and electrochemical characterization, nearly two‐thirds of them have also been studied by single‐crystal X‐ray diffraction and have had their EA s determined by low‐temperature gas‐phase photoelectron spectroscopy.…”

Corannulenes with Electron‐Withdrawing Substituents: Synthetic Approaches and Resulting Structural and Electronic Properties

“…Upon treatment of 1 with CF 3 I in the gas phase at temperatures above 100 °C, they even obtain symmetric, fivefold‐ substituted 1,3,5,7,9‐pentakis(trifluoromethyl)corannulene ( 7 a ) (Scheme ) . Recently, this procedure was also performed for longer chained R F substituents to obtain pentafluoroethyl derivative 7 b and perfluoropropyl compound 7 c . The authors present deeper insight into the gas‐phase trifluoromethylation of corannulene, and the structures and properties of some six‐ and sevenfold substituted (trifluoromethyl)corannulenes are also revealed .…”