Comprehensive photoelectron spectroscopic study of anionic clusters of anthracene and its alkyl derivatives: Electronic structures bridging molecules to bulk

Abstract

The evolution of the electronic structure of molecular aggregates is investigated using anion photoelectron (PE) spectroscopy for anionic clusters of anthracene (Ac) and its alkyl derivatives: 1-methylanthracene (1MA), 2-methylanthracene (2MA), 9-methylanthracene (9MA), 9,10-dimethylanthracene (DMA), and 2-tert-butylanthracene (2TBA). For their monomer anions (n=1), electron affinities are confined to the range from 0.47 to 0.59 eV and are well reproduced by density functional theory calculations, showing the isoelectronic character of these molecules. For cluster anions (n=2-100) of Ac and 2MA, two types of isomers I and II coexist over a wide size range: isomers I and II-1 (4< or =n<30) or isomers I and II-2 (n> or = approximately 40 for Ac and n> or = approximately 55 for 2MA). However, for the other alkyl-substituted Ac cluster anions (i.e., 1MA, 9MA, DMA, and 2TBA), only isomer I is exclusively formed, and neither isomer II-1 nor II-2 is observed. The vertical detachment energies (VDEs) of isomer I in all the anionic clusters depend almost linearly on n(-1/3). In contrast, the VDEs of isomers II-1 (n> or =14) and II-2 (n=40-100), appeared only in Ac and 2MA cluster anions, remain constant with n and are approximately 0.5 eV lower than those of isomer I. The PE spectra revealed the characteristics of each isomer: isomer I possesses a monomeric anion core that is gradually embedded into the interior of the cluster with increasing n. On the other hand, isomers II-1 and II-2 possess a multimeric (perhaps tetrameric) anion core, but they differ in the number of layers from which they are made up; monolayer (isomer II-1) and multilayers (isomer II-2) of a two-dimensionally ordered, finite herringbone-type structure, in which electron attachment produces only little geometrical rearrangement. Moreover, the agreement of the constant VDEs of isomer II-2 with the bulk data demonstrates the largely localized nature of the electronic polarization around the excess charge in a crystal-like environment, where about 50 molecules provide a charge stabilization energy comparable to the bulk.

Photoelectron spectroscopy of cluster anions of naphthalene and related aromatic hydrocarbons

“…In the course of our studies, we have found that isomers coexist in large anionic clusters of several oligoacenes: ͑naphthalene͒ n − , 32 ͑anthracene͒ n − , 32,33 and ͑tetracene͒ n − . 34 A photoelectron spectroscopy study of oligoacene cluster anions has revealed that the "crystal-like" clusters ͑referred to as "isomer II" in Ref.…”

“…34 A photoelectron spectroscopy study of oligoacene cluster anions has revealed that the "crystal-like" clusters ͑referred to as "isomer II" in Ref. Indeed, our recent study 33 reported that alkyl substitutions of anthracene molecules substantially influence the formation of isomer II through the operation of steric hindrance effects. These clusters coexist with isomer I, which has a higher vertical detachment energy ͑VDE͒.…”

Interruption of the inner rotation initiated in isolated electron-driven molecular rotors

“…3), so that it does not possess a broad conjugated π system. Correspondingly DAA is expected to behave under DEA similarly to a single anthracene molecule (EA a = 0.530 eV [26]), although the predicted EA a of DAA is somewhat higher (1.0 eV). Molecular negative ions of anthracene were only observed at thermal energy of the incident electrons, and the electron detachment time was estimated to be 25 μs [27].…”

Structural and spectroscopic study of adsorption of anthracene on silver

“…Delocalisation of the electron density between occupied NBOs and unoccupied NBOs corresponds to a stabilising donoracceptor interaction and can be quantitatively described in terms of the second-order perturbation interaction energy, E (2). Larger E(2) values indicate higher interactions between the electron donors and electron acceptors, and infer higher extent of conjugation of the whole system [40,41].…”

“…The unique properties of these organic compounds place them on the centre stage for the extensive range of applications in optoelectronic devices, such as organic light-emitting diodes, solar cells and field-effect transistors. Among the class of these polycyclic aromatic compounds, naphthalene, anthracene, tetracene and pentacene are considered as prototypical model systems for analysing charge localisation and transfers, both in experimental and in theoretical investigations [1][2][3]. Furthermore, the recent recognition of their promising potential as organic semiconductor materials in the design of devices based on electro-active organic molecules has generated an improved interest in their intrinsic structural, electronic and vibrational properties relevant to charge transfers and band gaps [4][5][6].…”