“…Van der Waals (vdW) complexes of aromatic molecules with rare gas atoms have been reported by many authors in recent years. − For the most part, the solvent spectral shift (SSS) due to microsolvation has been detected in strongly allowed transitions, where weak sidebands next to the main excitation band of the (unsolvated) molecule are observable. The formation of vdW complexes in an adiabatic expansion is dependent only on the expansion conditions (i.e.…”
Section: Introductionmentioning
confidence: 99%
“…It is not evident a priori whether a measurable solvent spectral shift of the triplet absorption energy of a thione is produced by microsolvation with a rare gas atom; the SSS could lie within the rotational envelope of the unsolvated band. vdW complexes involving aromatic thiones have been reported for the SSS of the strongly allowed S 0 → S 2 transition of xanthione and 4 H -1-benzopyran-4-thione (BPT). − Microsolvation shifts of spin-forbidden transitions have never been reported for thione compounds. In this paper an investigation of solvent spectral shifts in the T 1 → S 0 phosphorescence excitation spectra of jet-cooled BPT and 4 H -pyran-4-thione (PT) are presented, using direct S 0 → T 1 excitation.…”
The solvent spectral shifts of the S0 →
T1 origin bands of jet-cooled 4H-pyran-4-thione
(PT) and 4H-1-benzopyran-4-thione (BPT) were observed in phosphorescence excitation
spectra. Van der Waals complexes
(1:1) of seed molecules with the carrier gas were observed in several
rare gases. In all cases, the combination
of a dispersive red-shift and a dipole−induced dipole blue-shift
produced a total red-shift, up to a maximum
of δν̃ = −21 cm-1 for PT−Xe and
δν̃ = −30 cm-1 for BPT−Xe. Complexes
of 1:n (n > 1) were not
observable owing to the weakness of the direct S0 →
T1 transition. The inductive contributions to the
shifts
were calculated using values of excited-state dipole moments estimated
from solution Stokes shifts; the dipole
moments of both molecules in T1 were found to be close to
zero, significantly smaller than their ground-state
dipole moments. The phosphorescence excitation spectrum of
isolated PT is discussed in some detail. The
electronic origin of T1 at 16 844 cm-1 is
assigned to the transition S0,0 →
T1z,0; the transitions S0,0 ⇌
T1(x
y
),0
are too weak to be detected with this method. Vibronic transitions
S0,0 → T1z,v
in PT were
analyzed up to
excess energies of ∼hc1450
cm-1.
“…Van der Waals (vdW) complexes of aromatic molecules with rare gas atoms have been reported by many authors in recent years. − For the most part, the solvent spectral shift (SSS) due to microsolvation has been detected in strongly allowed transitions, where weak sidebands next to the main excitation band of the (unsolvated) molecule are observable. The formation of vdW complexes in an adiabatic expansion is dependent only on the expansion conditions (i.e.…”
Section: Introductionmentioning
confidence: 99%
“…It is not evident a priori whether a measurable solvent spectral shift of the triplet absorption energy of a thione is produced by microsolvation with a rare gas atom; the SSS could lie within the rotational envelope of the unsolvated band. vdW complexes involving aromatic thiones have been reported for the SSS of the strongly allowed S 0 → S 2 transition of xanthione and 4 H -1-benzopyran-4-thione (BPT). − Microsolvation shifts of spin-forbidden transitions have never been reported for thione compounds. In this paper an investigation of solvent spectral shifts in the T 1 → S 0 phosphorescence excitation spectra of jet-cooled BPT and 4 H -pyran-4-thione (PT) are presented, using direct S 0 → T 1 excitation.…”
The solvent spectral shifts of the S0 →
T1 origin bands of jet-cooled 4H-pyran-4-thione
(PT) and 4H-1-benzopyran-4-thione (BPT) were observed in phosphorescence excitation
spectra. Van der Waals complexes
(1:1) of seed molecules with the carrier gas were observed in several
rare gases. In all cases, the combination
of a dispersive red-shift and a dipole−induced dipole blue-shift
produced a total red-shift, up to a maximum
of δν̃ = −21 cm-1 for PT−Xe and
δν̃ = −30 cm-1 for BPT−Xe. Complexes
of 1:n (n > 1) were not
observable owing to the weakness of the direct S0 →
T1 transition. The inductive contributions to the
shifts
were calculated using values of excited-state dipole moments estimated
from solution Stokes shifts; the dipole
moments of both molecules in T1 were found to be close to
zero, significantly smaller than their ground-state
dipole moments. The phosphorescence excitation spectrum of
isolated PT is discussed in some detail. The
electronic origin of T1 at 16 844 cm-1 is
assigned to the transition S0,0 →
T1z,0; the transitions S0,0 ⇌
T1(x
y
),0
are too weak to be detected with this method. Vibronic transitions
S0,0 → T1z,v
in PT were
analyzed up to
excess energies of ∼hc1450
cm-1.
“…(ii) Structures and Binding Energies of the Complexes. The structures and binding energies of the 1:1 and 1:2 ClAz·RG, MAz·RG, and DMAz·RG complexes in their ground electronic states were calculated using Lennard-Jones 6−12 potential functions in a manner described in detail in previous publications. , In these calculations, the structures of the bare chromophores were obtained by ab initio methods and were fixed at their optimum geometries . The binding energy was then calculated as a function of the position(s) of the adatom(s) on the molecule's surface(s).…”
The
S2−S0(1La)
fluorescence excitation and emission spectra of the van der Waals
complexes of three azulene
(Az) derivatives, 2-chloroazulene (ClAz), 2-methylazulene (MAz), and
1,3−dimethylazulene (DMAz), with
the rare gases, Ar, Kr, and Xe, have been measured under jet-cooled
conditions. The microscopic solvent
shifts, δν̄, of the origin bands in the
S0−S2 spectra associated with complexation of
the chromophores with
one and two rare gas atoms increase with increasing polarizability of
the adatom(s), consistent with the
dominance of dispersion in the binding. Although there are
substantial variations in the relative values of
δν̄
among the Az derivatives examined, all of the δν̄ values are
relatively small and are similar to those of the
1Lb(S0−S1)
transitions in the rare gas complexes of naphthalene and its
methyl-substituted derivatives. The
theory of microscopic solvent shifts of Jortner et al. has
been used to analyze the solvent shift data.
Comparisons of the sources of the oscillator strengths and van der
Waals binding interactions in the azulene−
and naphthalene−rare gas systems are revealing and suggest that the
variations in δν̄ with substitution pattern
are primarily electronic in their origin and arise from variations in
excited state configuration interactions,
the magnitude of which depend on the
S2−S
n
energy spacings. These
spacings can be varied by placing
substituents either along the long axis (2-position) or parallel to the
short axis( 1,3-positions) so that they
selectively perturb, respectively, the long axis polarized and the
short axis polarized transitions. The structures
and binding energies of the complexes of these derivatives have also
been modeled using Lennard-Jones type
calculations and have been compared with those of Az itself. The
observed progressions in the low-frequency
intermolecular vibrations in each case are assigned to that excited
state bending mode which is parallel to the
long axis of the chromophore, in agreement with model calculations
using one-dimensional Morse and Taylor's
series potential functions.
“…Laser-induced fluorescence excitation spectra of TRN(CO 2 ) n van der Waals complexes were obtained with a pulsed supersonic free-jet spectrometer which has previously been described in detail. , Briefly, the excitation source for this spectrometer is a Lumonics Hyperdye 300 pulsed dye laser pumped by a Lumonics HyperEX 400 XeCl excimer laser. Exalite 376 (4 × 10 -4 M in p -dioxane) and a mixture of BBQ and BPBD (1 × 10 -4 M BBQ and 6.2 × 10 -4 M BPBD in 2:3 v:v toluene:ethanol) were used to cover the excitation wavelength ranges required for this study.…”
van der Waals complexes of tropolone (TRN) with carbon dioxide have been synthesized by expanding mixtures
of TRN and CO2 in He in a supersonic free-jet expansion, and have been examined by laser-induced
fluorescence excitation spectroscopy and by ab initio structural calculations. At higher partial pressures of
CO2 large clusters of TRN(CO2)
n
are formed in which TRN excited to S1 remains fluorescent. At sufficiently
low partial pressures of CO2, well-resolved blue-shifted features in the spectra due to TRN(CO2) and TRN(CO2)2 may be identified. Their microscopic solvent shifts and the effects of solvation on the proton tunneling
doublets and vibrational frequencies of the chromophore have been measured. The experimental results and
calculations all suggest that the CO2 binds to TRN in the 1:1 complex in a fashion which is similar to common
hydrogen-bonding addends. The CO2 lies in the plane of the TRN ring and interacts with the keto oxygen
and the hydroxyl hydrogen in such a way that the intramolecular hydrogen bond of TRN is partially disrupted,
lengthening the R
O- - -H distance and opening the H−O−C angle. Consistent with this interaction, the proton
tunneling rate is reduced so that the tunneling doublets can no longer be resolved, and the frequency of the
out-of-plane wagging vibration of the two oxygen atoms in the chromophore increases. The microscopic
solvatochromic shifts of these and other hydrogen-bonded complexes are well-correlated with the calculated
binding energies of the addends to the chromophore and with their proton affinities. The latter correlation
suggests that CO2 acts as a weak proton acceptor in a hydrogen-bonding-like interaction with TRN.
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