Tandem mass spectrometry of π‐expanded triphenylamine and N‐heterotriangulene scaffolds: Radical cation versus silver(I) adduct

Abstract

Triphenylamine (TPA) and N‐heterotriangulene (N‐HTA) scaffolds with up to three oligophenyl extensions are investigated by electrospray ionization (tandem) mass spectrometry (ESI‐[MS/]MS). Due to their low oxidation potentials, all molecules readily form radical cations in the electrospray process. The energy‐resolved collision‐induced dissociation behaviour of the molecular ions is contrasted to that of the silver(I) adducts. Complexation with Ag(I) leads to the expected [1:1] and [2:1] complexes (MAg+ and M2Ag+); however, even [1:2] complexes (MAg22+) can be detected for molecules with two and three large π‐expansions to allow stabilization of two charges. The TPA scaffolds decompose only at high collision energies through the loss of peripheral tert‐butyl groups. A general mechanism for this is proposed commencing with a methyl loss and followed by the release of isobutene and butyl radical moieties. The N‐HTA‐based scaffolds are considerably less stable and molecular ions fragment at low collision energies. This is caused by the facile loss of methyl radicals from the dimethylmethylene‐bridged triangulene core. In contrast, complexation with Ag+ leads to a dramatic stabilization. Most interestingly, dissociation eventually proceeds via the loss of neutral AgCH3, which is indicative of strong bidentate, tweezer‐like bonding of Ag+ to the molecules.