Substituent Effects on the Electronic Characteristics of Pentacene Derivatives for Organic Electronic Devices: Dioxolane-Substituted Pentacene Derivatives with Triisopropylsilylethynyl Functional Groups

Abstract

The intramolecular electronic structures and intermolecular electronic interactions of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene), 6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]-pentacene (TP-5 pentacene), and 2,2,10,10-tetraethyl-6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (EtTP-5 pentacene) have been investigated by the combination of gas-phase and solid-phase photoelectron spectroscopy measurements. Further insight has been provided by electrochemical measurements in solution, and the principles that emerge are supported by electronic structure calculations. The measurements show that the energies of electron transfer such as the reorganization energies, ionization energies, charge-injection barriers, polarization energies, and HOMO-LUMO energy gaps are strongly dependent on the particular functionalization of the pentacene core. The ionization energy trends as a function of the substitution observed for molecules in the gas phase are not reproduced in measurements of the molecules in the condensed phase due to polarization effects in the solid. The electronic behavior of these materials is impacted less by the direct substituent electronic effects on the individual molecules than by the indirect consequences of substituent effects on the intermolecular interactions. The ionization energies as a function of film thickness give information on the relative electrical conductivity of the films, and all three molecules show different material behavior. The stronger intermolecular interactions in TP-5 pentacene films lead to better charge transfer properties versus those in TIPS pentacene films, and EtTP-5 pentacene films have very weak intermolecular interactions and the poorest charge transfer properties of these molecules.

(Electro)chemical Oxidation of 6,13‐Bis[tri(isopropyl)silylethynyl]pentacene to its Radical Cation and Dication

“…[22] Conversely,c hanging the solvent from CH 2 Cl 2 to THFc auses as ignificant positive shift in E 0 (I) by almost 160 mV (after referencing to E 0 (Fc/Fc + )i nt he respective solvent). [22] Conversely,c hanging the solvent from CH 2 Cl 2 to THFc auses as ignificant positive shift in E 0 (I) by almost 160 mV (after referencing to E 0 (Fc/Fc + )i nt he respective solvent).…”

“…The results were provent o be fabricated and later had to be retracted. [10,11] Both the high charge-carrier mobility [10,11] and the HOMO-LUMO gap [19][20][21][22][23] suggest applications for acenes as possible "successors to traditional inorganic semiconductors." [10,11] Both the high charge-carrier mobility [10,11] and the HOMO-LUMO gap [19][20][21][22][23] suggest applications for acenes as possible "successors to traditional inorganic semiconductors."…”

“…However,previouscyclic voltammetric studies have provided only limited information.K inetic and persistence informationa nd identification of the oxidationp roduct(s) and their further reaction or oxidation have not been reported. [22,[33][34][35] For dimesitylpentacene 1c,t he high persistence of the neutralp arentm olecule and its radical cation were recently highlighted. The electrochemically and chemically generated radicalc ation of the title compound was char-acterizedb yu sing ESR andU V/Vis/NIR spectroscopy and quantum-chemical modeling.…”

“…[21] Usually onset potentials of oxidation andr eduction, [34] differential pulse voltammetric peak potentials, [20][21][22] or formal potentials E 0 derived from cyclic voltammetric peak potentials [33,34,49] are the basic information. Analysis of the relationship between ultraviolet photoelectrons pectroscopic ionization energies and electrochemical potentials indicated the effects of various internal and environmental factors.…”

“…[17,18] As ac onsequence, however,t his acene andi ts derivatives have been particularly well studied with respectt ot heir structural, chemical, and physical properties. [10,11] Both the high charge-carrier mobility [10,11] and the HOMO-LUMO gap [19][20][21][22][23] suggest applications for acenes as possible "successors to traditional inorganic semiconductors." [24] Acene-based devices now indeed demonstrate higherf ield-effect mobilities than those based on amorphous silicon.…”