Electronic Properties of Pentacene versus Triisopropylsilylethynyl-Substituted Pentacene: Environment-Dependent Effects of the Silyl Substituent

Abstract

Energy measures of the intra- and intermolecular electronic effects of triisopropylsilylethynyl substitution on pentacene have been obtained from the combination of closely related gas phase and solid phase ultraviolet photoelectron spectroscopy (UPS) measurements along with solution electrochemical measurements. The results show that the shift to lower ionization energy that is expected with this substitution and observed in the gas phase measurements becomes negligible in solution and is even reversed in the solid phase. The principles that emerge from this analysis are supported by electronic structure calculations at the density functional theory level. The relation between the gas phase and solid phase UPS measurements illustrated here provides a general approach to investigating the electronic effects acting on molecules in the condensed phase, which in this case are greater than the direct substituent electronic effects within the molecule. Electronic properties such as lower ionization energies built into the single-molecule building blocks of materials and devices may be reversed in the solid state.

Unraveling Unprecedented Charge Carrier Mobility through Structure Property Relationship of Four Isomers of Didodecyl[1]benzothieno[3,2‐b][1]benzothiophene

“…To the best of our knowledge, these results provide the fi rst experimental report of an IP variation as large as 0.6 eV among isomers. Note that an increase as large as 1.0 eV in the ionization potential was observed by ultraviolet photoelectron spectroscopy (UPS) going from pentacene to TIPS-pentacene, [ 31 ] as further supported by theoretical calculations. [ 30 ] Such a result highlights the importance of considering intermolecular interactions in the evaluation of the ionization potential or electron affi nity in crystalline fi lms and hence when assessing the ease of charge injection from electrodes.…”

Ionization Energies, Electron Affinities, and Polarization Energies of Organic Molecular Crystals: Quantitative Estimations from a Polarizable Continuum Model (PCM)-Tuned Range-Separated Density Functional Approach

“…To illustrate this behavior, Figure S1 in the SI shows the fraction of eX in various functionals versus the inter-electronic distance r 12 . In the following, we take the tuned ω value for pentacene as an example.…”

“…As a consequence, the physical interpretation of these measurements can remain controversial. 11 To take a recent example involving two widely studied organic semiconductors, the IE of the pentacene crystal has been measured by the Lichtenberger group to be 4.81 eV 12,13 , which is 0.24 eV smaller than the IE measured by the Kahn group (5.05 eV) 14,15 ; on the other hand, the IE of tri-isopropylsilylethynyl (TIPS)-pentacene determined by the Lichtenberger group (5.84 eV) 12,13 is 0.80 eV larger than that reported by the Kahn group (5.04 eV) 14,15 . As a result, the solid-state polarization energies estimated for the TIPS-pentacene films are remarkably different: 0.44 eV by the Lichtenberger group vs. 1.24 eV by the Kahn group.…”

Relating the Physical Structure and Optoelectronic Function of Crystalline TIPS‐Pentacene

“…[ 19,56,57 ] Table 2 presents the computed TIPS-PEN gas-phase and bulk crystalline fundamental gap, that is, the electron addition-removal gap. The gas-phase gap (which is equal to the difference between the molecule's ionization energy and electron affi nity) of 4.0 eV in TIPS-PEN is 0.5 eV smaller than the 4.5 eV predicted for PEN within the same level of theory.…”