Clustering of pentacene and functionalized pentacene ions in a matrix-assisted laser desorption/ionization orthogonal TOF mass spectrometer

Abstract

A high-performance orthogonal time-of flight (TOF) mass spectrometer, in combination with the matrix assisted laser desorption/ionization (MALDI) source operating at elevated pressure ( approximately 1 torr in N(2)), was used to perform MALDI-TOF analyses of pentacene and some of its derivatives with and without an added matrix. These molecules are among the most interesting semiconductor materials for organic thin film transistor applications (OTFT). The observation of ion-molecule reactions between "cold" analyte ions and neutral analyte molecules in the gas phase has provided some insight into the mechanism of pentacene cluster formation and its functionalized derivatives. Furthermore, some of the matrices employed to assist the desorption/ionization process of these compounds were observed to influence the outcome via ion-molecule reactions of analyte ions and matrix molecules in the gas phase. The stability and reactivity of the compounds and their clusters in the MALDI plume during gas-phase expansion were evaluated; possible structures of the resulting clusters are discussed. The MALDI-TOF technique was also helpful in distinguishing between two isomeric forms of bis-[(triisopropylsilyl)-ethynyl]-pentacene.

Superbenzene–Porphyrin Conjugates

“…Clusters of compound 5 were observed previously in a dedicated high-pressure MALDI experiment, which promoted ion/molecule reactions and proved the existence of pentacene aggregates of the type (5) n + C with up to n = 5. [11] However, under the present conditions, neither 5 nor 6 show signs of higher aggregates, while 3 shows efficient cluster formation, underpinning the propensity of 3 to form aggregates under the applied conditions.…”

Aggregation of a Crown Ether Decorated Zinc–Phthalocyanine by Collision-Induced Desolvation of Electrospray Droplets

“…Though gas-phase clusters of aromatic compounds have been observed before, they were generated via either pulsed adiabatic expansion , or laser desorption/ionization , combined with collisional cooling, the aggregation to multiply charged clusters containing up to 22 molecules in a simple ESI experiment is unprecedented. The relatively flat structure of the crown ether substituted Pcs is certainly one reason for the effortless aggregation.…”

“…As the background pressure of the instrument consists for the most part of evaporated solvent molecules and nitrogen gas, such a high degree of constructive ion/molecule and ion/ion reactions was considered to be highly improbable. Though gas-phase clusters of aromatic compounds have been observed before, they were generated via either pulsed adiabatic expansion 44,45 or laser desorption/ionization 46,47 combined with collisional cooling, 48 ) in solution. 49−52 The unpaired electron is evenly distributed between the two molecules, resulting in charge resonance stabilization of the radical cation dimer.…”

Superbenzol‐Porphyrin‐Konjugate

“…Pentacen (5) wurde bereits in einem Hochdruck-MALDI-Experiment, das Ion/ Molekül-Reaktionen induziert, zum Aggregieren gebracht, wobei Cluster des Typs (5) n + C mit n maximal 5 entstanden. [11] Unter den von uns genutzten Bedingungen zeigte aber weder 5 noch 6 Anzeichen von Aggregation, wohingegen 3 effizient Cluster bildete, was die hohe Neigung von 3 zur Clusterbildung betont.…”