S₂−S₀ Spectroscopy of the van der Waals Complexes of Azulene with Rare Gases

Abstract

The S 2 -S 0 fluorescence emission and excitation spectra of jet-cooled azulene and its complexes with the rare gases, Ne, Ar, Kr, and Xe, have been measured. Features due to AZ‚RG n (n ) 1-4 when RG ) Ar, Kr, Xe and n ) 1 when RG ) Ne) are observed in the S 2 -S 0 fluorescence excitation spectra when azulene is coexpanded with the rare gases. The microscopic solvent shifts, δν j, of the origin bands for each complex scale linearly with the polarizability of the adatom(s), indicating that binding is dominated by dispersive interactions. This conclusion has been confirmed in calculations of the separate contributions of dispersion and induction to δν j. Mildly anharmonic progressions in very low frequency excited-state intermolecular (van der Waals) modes are attached to the origin bands of each AZ‚Kr n and AZ‚Xe n complex. The dominant progression is assigned to single quantum changes in that excited-state bending mode which involves motion of the adatom(s) in the plane perpendicular to the azulene ring containing the long (x) axis of the molecule. This assignment has been confirmed by calculating the frequencies of the bending and stretching vibrations in the ground state by using one-dimensional Morse and Taylor's series potential functions. The most stable geometries of the n ) 1-4 complexes in their ground states have been calculated by using a summation of pairwise atom-atom Lennard-Jones 6-12 potentials. The potential minima of the 1:1 complexes are located over the seven-membered ring; no second minimum is found over the five-membered ring. The most stable 1:2 species appears to be the symmetric (1 + 1) complex in which one adatom is bound on each side of the azulene surface. Some evidence of the asymmetric (2 + 0) isomer is also found.

S2–S0Spectra of Jet-Cooled Xanthione and Benzopyranthione: Microscopic Solvation by Rare Gases

“…With the cross-sections of the potential surface in the x, y, and z where a u , a £ are the polarizabilities and N u , N £ are the effecdirections in hand, each one-dimensional potential was aptive numbers of electrons on atoms u and £. The repulsive proximated by both a Morse function and a Taylor series term for two like atoms is given by expanded about the equilibrium distance R 0 , as described in detail in previous publications (21,27).…”

Vibrational energy relaxation of azulene in the S2 state. II. Solvent density dependence

“…Since the S 0 and the S 2 states are combined by the direct photoinduced transitions, we can estimate the difference of the solute-solvent interactions of S 0 and S 2 states from the frequency shift of the optical spectra. According to the study on the fluorescence excitation spectra of the azulene-C 2 H 6 and the azulene-Xe van der Waals ͑vdW͒ 1:1 complexes, the shifts of the 0-0 bands are Ϫ45.5 cm Ϫ1 and Ϫ54 cm Ϫ1 for azulene-Xe 42 and azulene-C 2 H 6 43 complexes, respectively. These shifts correspond to the differences of the binding energies of the solute-solvent binary potentials, if the bottom of the solutesolvent potential of the excited state exists within the Franck-Condon accessible region.…”

Dynamics of electronic energy transfer from the S2 state of azulene to the S2 state of zinc porphyrin

“…This anomalous behaviour has led to several studies devoted to the spectroscopic characterisation of azulene. 2,3 Recently, several azulenic derivatives were synthesised, 4 and used to understand the colour properties of their bacteriorhodopsin analog. 5 Porphyrin-based systems are commonly employed for gaining further insight into the efficient photon-harvesting and electron transfer dynamics of the photosynthetic apparatus.…”