Photoelectron spectra of acenes. Electronic structure and substituent effects

Abstract

The valence-electronic structure of the first three members of the acene series, benzene, naphthalene and anthracene, seems to be confirmed now by their photoelectron (PE) spectra. This especially holds for the r-ionizations which, according to their specific behaviour, can be assigned to different ionization modes. The vibrational fine structure of the observed systems is discussed. The effects of a series of substituents on the electronic structure of the parent molecules were traced in their PE spectra and intercompared. The results for methyl, chloro, methoxy and cyano substitution are described in detail.The effect is most pronounced for the two lowest energy -ionizations (i.e. HOMO and SHOMO in the Koopmans' picture) and can be described by the shift of the mean energy ("center of gravity") of HOMO and SHOMO, and the additional splitting compared to the unsubstituted molecule. Both parameters show good linear dependence for the three series of compounds, thus allowing to formulate general substituent parameters. A linear dependence of the lowest ionization energy with Hammett constants is found to exist as well.

Electron transfer from anthracenes. Comparison of photoionization, charge-transfer excitation and electrochemical oxidation

“…1 for 9-acetoxy, 9-bromo, and 9,lO-dibromoanthracene. The reliability in the values of El and that of the second ionization energy E2 listed in Table 1 was established by a comparison with those obtained independently by Klasinc and co-workers (10). The trend, as reported earlier, is for both El and E2 to generally increase with values of the Hammett a constant -that is, the presence of electron-attracting substituents leads to the stabilization of the HOMO as well as the SHOMO.…”

“…The comparison of the He(1) and He(I1) photoelectron spectra of anthracene with those of benzene and naphthalene has established the first ionization El at 7.43 eV to occur from a T-orbital (HOMO according to Koopmans' theorem) of b2, symmetry with maximum electron density at the 9-and 10-positions (10). The second ionization E2 at 8.53 eV occurs from the subjacent T-orbital (SHOMO) of big symmetry with a node at the 9-and 10-positions.…”

“…This series of aromatic compounds is particularly well suited to study the relationships among the various measures of electron detachment both in the gas phase and in solution. Thus the anthracenes are sufficiently volatile for the photoelectron spectra to be measured directly in the gas phase (10). Moreover, they form an extensive series of EDA complexes with tetracyanoethylene or TCNE, in which the charge transfer absorption bands are exceptionally well resolved from those of the components (1 I).…”

Charge transfer emissive singlet excited states and photoinduced electron transfer properties in the diarylideneacetone compounds (RCHCH)2CO; R = phenyl, 1- and 2-naphthyl, 3-(N-ethylcarbazoyl), and 4-(C5H5)Fe(C5H4C6H4CHCH(CO)CHCHC6H5)

“…Recent literature data have shown that the CT band energies arising from interactions between different aromatic compounds (donors) and the tropylium cation (acceptor) follow a linear relationship with the IP of the aromatics (20). Figure 2 shows the same dependence of the transition energies of the CT bands in the diarylideneacetones on the IP of the aromatic compounds (21). This experiment indicates that the aryl groups are indeed the donors, and the (CHCH)*CO group is the acceptor moiety of the CT interactions.…”

Investigation of Aromaticity of Tri and Tetraazanaphthalene Derivatives

“…Naphthalene is composed of two fused benzenes, and it has been studied frequently with its derivatives for about fifty years, since 1968 (Yencha & El-Sayed, 1968;Kitagawa, 1968;Kaim, Tesmann & Bock, 1980;Klasinc, Kovac & Gusten, 1983;Meylan & Howard, 1991;Heinis, Chowdhury & Kebarle, 1993;Schiedt, Knott, Barbu, Schlag & Weinkauf, 2000;Lardin, Squires & Wenthold, 2001;Song, et al 2002). Ghiasi (Ghiasi, 2005) worked on the aromaticity of mono-and di-silanaphthalene after the first achievement of the synthesis of 1-Silanaphthalene was published by Takeda et al (Takeda, Shinohara & Tokitoh, 2002).…”