The Lowest Excited Singlet States of 1-Azaadamantane and 1-Azabicyclo[2.2.2]octane:  Fluorescence Excitation Spectroscopy and Density Functional Calculations

Abstract

The lowest excited singlet states of the structurally rigid amines 1-azaadamantane and 1-azabicyclo[2.2.2]octane have been investigated by using fluorescence excitation spectroscopy on samples seeded in supersonic expansions. Based upon the notion that in both species the lowest excited singlet state is a Rydberg state with the ground state of the radical cation as its ionic core, excitation spectra have been analyzed by employing density functional calculations of the equilibrium geometries and force fields of the ground state of the neutral species and its radical cation. A good agreement is obtained between experimentally observed and theoretically predicted frequencies and intensities of vibronic transitions. Subsequent refinements of the geometry of the lowest excited singlet state are shown to account adequately for the minor differences between experiment and the computational results obtained by using the radical cation as a model for the lowest excited singlet state. From our analysis it also becomes apparent that the excited state is in both molecules subject to vibronic coupling with higher-lying excited states, as exemplified by the presence of transitions to non-totally symmetric vibrational levels. The results of the present study enable the determination of mode-specific reorganization energies accompanying ionization of 1-azaadamantane, which are shown to correspond qualitatively well with those determined in resonance Raman studies on the charge transfer transition in the electron donor−acceptor system 1, which contains 1-azaadamantane as the electron donor unit.

Excited and ionic states of formamide: An excited-state photoelectron spectroscopy and ab initio study

“…Since the equilibrium geometry and force field of Rydberg states converging upon D 0 generally closely resemble those of D 0 , the Franck-Condon calculations also give a strong indication of the vibrational activity we may expect to see in their excitation spectra, as has been amply demonstrated in recent studies on nitrogen-containing cage compounds. [47][48][49][50] The present calculations thus tell us to anticipate dominant activity of the 5 and 4 modes. The calculated Duschinsky matrix shows at the same time that the distribution of activity over these two modes is rather susceptible to the precise magnitude of the normal-mode rotations.…”

Adhesion of protein residues to substituted (111) diamond surfaces: An insight from density functional theory and classical molecular dynamics simulations

“…The average CN bond length in the N‐substituted cluster was calculated to be 150.8 pm. This is notably longer than the corresponding bond computed in 1‐azaadamantane at the B3LYP/6‐311G* level, 147.3 pm 43. The average SiC bond length in the Si‐substituted cluster was found to be 182.6 pm.…”

“…This is notably longer than the corresponding bond computed in 1azaadamantane at the B3LYP/6-311G* level, 147.3 pm. 43 The average SiÀ ÀC bond length in the Si-substituted cluster was found to be 182.6 pm. This is considerably shorter than the SiÀ ÀC bond lengths observed in 1-methyl-1-silaadamantane by electron diffraction, 187.9(3) pm.…”

Fast photodynamics of azobenzene probed by scanning excited-state potential energy surfaces using slow spectroscopy

“…In general, such differences indicate that the geometry changes upon excitation are not predicted accurately enough. To get an idea of the geometry changes that would lead to consistency with the experimentally observed excitation spectrum, we have employed the observed intensities of transitions to ‘reconstruct’ the equilibrium geometry of the S 1 (nπ*) state 39 40 . In our experiments, we primarily observe Franck–Condon activity of bending vibrations and not of CC and CN stretch vibrations, which, as will be argued below, is attributed to the opening up of an additional non-radiative decay channel at these vibrational energies.…”