Paracyclophanes as model compounds for strongly interacting π-systems. Part 1. Pseudo-ortho-dihydroxy[2.2]paracyclophane

Abstract

In this work we describe a study of the ground and first excited state structures and energetics of a dihydroxy-derivative of [2.2]paracyclophane (PC), the pseudo-ortho-dihydroxy[2.2]paracyclophane (o-DHPC), also termed 4,12-dihydroxy[2.2]paracyclophane. In order to understand the electronic interactions between the two pi-systems, the molecule is investigated by REMPI spectroscopy in a free jet and by quantum chemical calculations. REMPI-spectra of the cluster with one water molecule were also obtained and aid in the interpretation. The origin of the S(1) <-- S(0) transition lies at 31,483 cm(-1) (3.903 eV) for o-DHPC and 31,263 cm(-1) (3.876 eV) for the o-DHPC x H(2)O cluster. An adiabatic excitation energy of 3.87 eV was computed for the S(1) <-- S(0) transition in o-DHPC. The SCS-CC2 calculations deviate by less than 0.1 eV for the adiabatic excitation energies of PC, o-DHPC and the related aromatic molecules benzene and phenol. Considerable activity in a breathing vibration of 190 cm(-1) is found in the S(1) state of o-DHPC and o-DHPC x H(2)O, in agreement with the computed SCS-CC2 value of 185 cm(-1). Further vibrations appear at +11 cm(-1) and +54 cm(-1) in o-DHPC. The computations and the available experimental data of the parent PC show that both PC and o-DHPC are rather flexible with respect to motions of the benzene moieties.While PC has a double minimum potential energy with respect to the torsional motion, a single-minimum structure is found for the ground state of o-DHPC. The geometry change upon excitation is less pronounced in o-DHPC as compared to PC. Two of the three possible rotational conformers of the OH groups were found to have similar energies, but spectral hole burning shows that the spectra are dominated by a single rotamer.

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

“…The detailed setup of the apparatus has been described in a previous publication. 42 In the experimental chamber the molecules were ionized by a picosecond laser with a repetition rate of 10 Hz. The details of the laser system, consisting of a solid state Nd:YLF (neodymium-doped yttrium lithium fluoride) laser and an optical parametric generator (OPG), are also given elsewhere.…”

Electronic Structure and Excited‐State Dynamics of an Arduengo‐Type Carbene and its Imidazolone Oxidation Product

“…For the time‐resolved experiments t Bu 2 Im was heated up to 70 °C (benzimidazolone up to 220 °C) in a self‐built oven attached to a pulsed solenoid valve. The molecules were expanded with argon as a carrier gas ( p 0 (Ar)=1.3–1.6 atm) into a differentially pumped vacuum chamber, described in detail in a previous publication . The experiments on benzimidazolone were performed in a different, but similar apparatus.…”

“…The molecules were expanded with argon as ac arrier gas (p 0 (Ar) = 1.3-1.6 atm) into ad ifferentially pumped vacuum chamber,d escribed in detail in ap revious publication. [26] The experiments on benzimidazolone were performed in ad ifferent, but similar apparatus. The molecules were excited and ionized by picosecond pulses provided by an Ekspla laser system operating at 10 Hz repetition rate.…”

Excited‐State Dynamics of the 2‐Methylallyl Radical

“…The experiments were carried out in a standard molecular beam apparatus equipped with a Wiley‐McLaren time‐of‐flight mass spectrometer described previously 17. Briefly, we generated a clean beam of 2‐methylallyl radicals by pyrolysis of 3‐bromo‐2‐methylpropene, obtained from Sigma Aldrich.…”

“…The experiments were carried out in a standard molecular beam apparatus equipped with a Wiley-McLaren time-of-flight mass spectrometer described previously. [17] Briefly, we generated a clean beam of 2-methylallyl radicals by pyrolysis of 3-bromo-2-methylpropene, obtained from Sigma Aldrich. The precursor is seeded in 1.2 to 1.4 bar of argon and expanded through a SiC tube of 1 mm diameter mounted onto a solenoid valve with a nozzle of 0.8 mm diameter, operating at 10 Hz.…”