Magnetic circular dichroism of cyclic .pi.-electron systems. 14. Derivatives of azulene

Abstract

of Derivatives of Azulene with confidence that its unobserved third excited singlet state lies near 34 000 cm-1, between the La and Bb bands. The existence of this state has been recently deduced from a study of azapyrenes,8 and may be of interest for interpretation of two-photon absorption work.Similarly, our data also show quite unambiguously the presence of a transition near 40 000 cm-1 (transition 5) in pyrene derivatives and, again by extrapolation, in pyrene itself.The existence of this weak transition has been suspected for some time15 and was substantiated also in our MCD study of azapyrenes.8 About four weak transitions are calculated in this region by the PPP method.Finally, and not surprisingly, our MCD data show that the absorption region of the Ba transition is composite and contains several transitions. These may correlate with some of the four mentioned above, with another four or so calculated at somewhat higher energies, or with transitions into states of partially doubly excited nature which do not appear in the simple PPP approximation used here. ConclusionsThe simple theory of parts 1-34™6 accounts well for the qualitative features of the MCD spectrum of pyrene and, even semiquantitatively, for the substituent effects on the Lb, La, and Bb bands. The experimental data permit a conclusive identification of two new transitions near 34 000 cm-1 and near 40 000 cm-1 in pyrene derivatives and, by extrapolation, in pyrene itself, as well as a more tentative identification of several new excited states at higher energies.

Time-dependent photoionization of azulene: Competition between ionization and relaxation in highly excited states

“…This would be consistent with the doubly excited state revealed in MCD around 4.95 eV. 24 In such a case, internal conversion would be expected to favour population transfer to Rydberg states with a large binding energy. We can tentatively assign the electronic configuration of this doubly excited state.…”

“…The general concept of a "superexcited state" defines a neutral state higher than the ionization potential with two-electron holes or an inner-shell electron. 32 Detailed experimental and theoretical data on the ionization of azulene are scarce, 21,22,33,34 but the onset of shake-up ion states has been calculated by Deleuze to lie at quite low excitation energies, around 9.6 eV with a dominant configuration corresponding to ( ) ( ) ( ) ( ) ( ) ( ) ( ) 24 This kind of state is not strictly speaking a SES since it lies below the IP, but some of the properties of such a state are very similar to a SES. Now we will demonstrate why the photoelectron spectra of This two-photon ionization channel (path(e)) would also be strongly favoured because of inefficient Franck-Condon factors from S 2 onto D 0 (path(d)) as a result of insufficient energy to achieve vibrational energy conservation (as shown in Eq.…”

“…The presence of a doubly excited state lying at an energy as low as 4.95 eV has been detected by magnetic circular dichroism (MCD) on different derivatives of azulene. 24 This kind of state is not strictly speaking a SES since it lies below the IP, but some of the properties of such a state are very similar to a SES. Now we will demonstrate why the photoelectron spectra of Fig.…”

Communication: Existence of the doubly excited state that mediates the photoionization of azulene

“…We note that doubly excited states at energies as low as 4.95 eV have been detected by the magnetic circular dichroism experiments on azulene derivatives. 21 By computing a large number of singlet excited states (for the lowest 10 states found, see Table I) at the high level of the equation-of-motion coupled-cluster (EOMCC) theory 22 capable of capturing the singly and doubly excited states, abbreviated as δ-CR-EOMCC(2,3), 23 we have confirmed the existence of the postulated doubly excited state. The number of electronic states we had to converge had to be much larger than in the case of the earlier complete-active-space self-consistent-field (CASSCF) and multi-reference perturbation theory CASPT2 calculations of the low-lying excitations in azulene dominated by one-electron transitions.…”

Collisional energy transfer probabilities of highly excited molecules from KCSI. III. Azulene: P(E′,E) and moments of energy transfer for energies up to 40 000 cm−1 via self-calibrating experiments

“…2 shows several electronic transitions: S 0 →S 1 ͑origin 14 283.3 cm Ϫ1 ͒, 16 S 0 →S 2 ͑origin 28 757 cm Ϫ1 ͒, 17,18 S 0 →S 3 ͑origin Ϸ34 000 cm Ϫ1 ͒, S 0 →S 4 ͑origin Ϸ36 000 cm Ϫ1 ͒, and S 0 →S 5 ͑origin Ϸ42 000 cm Ϫ1 ͒. [19][20][21] Optical excitation to S 1 results in an efficient, ultrafast internal conversion back to S 0 ( IC Ϸ1), with a rate constant k IC ϭ1 ϫ10 12 s Ϫ1 at the origin. 22,23 This value was recently questioned by Ruth et al, who find a smaller k IC ϭ3.8 ϫ10 11 s Ϫ1 .…”