Intramolecular electronic interaction in ethereal bichromophoric EDA systems in supersonic free jet

Article abstract of DOI:10.1021/jp9609500

Excited-state charge transfer interaction was studied in bichromophoric electron donor-acceptor (EDA) systems, 1- and 9-(p-N,N-(dimethylamino)phenylethyloxy)anthracenes (1- and 9-An-O(CH₂)₂-DMA) and 1- and 9-(p-N,N-(dimethylamino)ben

Full text of DOI:10.1021/jp9609500

J. Phys. Chem. A 1997, 101, 31-35
31
Intramolecular Electronic Interaction in Ethereal Bichromophoric EDA Systems in
Supersonic Free Jet
Norikazu Tsujiya, Kiyoe Kitaura, Yae Kumamoto, and Michiya Itoh*
Department of Physical and Chemical Biodynamics, Graduate School, and Faculty of Pharmaceutical
Sciences, Kanazawa UniVersity, Takara-machi, Kanazawa 920, Japan
ReceiVed: March 29, 1996; In Final Form: September 10, 1996X
Excited-state charge transfer interaction was studied in bichromophoric electron donor-acceptor (EDA) systems,
1- and 9-(p-N,N-(dimethylamino)phenylethyloxy)anthracenes (1- and 9-An-O(CH2)2-DMA) and 1- and 9-(p-
N,N-(dimethylamino)benzyloxy)methylanthracenes (1- and 9-An-CH2OCH2-DMA), in supersonic expansion.
Intramolecular exciplex fluorescence, depending on excess vibrational energy, was observed in jet-cooled
9-An-O(CH2)2-DMA. In 1-An-O-(CH2)2-DMA, the existence of two isomeric conformers was observed in
fluorescence excitation spectra. The UV fluorescence excitation spectrum shows well-resolved vibrational
structures, while the visible fluorescence excitation spectrum exhibits considerably broad and 4.5 nm blue-
shifted vibrational structures from the UV excitation spectrum. The latter visible excitation spectrum is
attributable to intramolecular van der Waals interaction between EDA moieties followed by the exciplex
formation. Another conformer exhibits no significant exciplex fluorescence. The other ethereal compounds,
1- and 9-An-CH2OCH2-DMA, exhibit neither exciplex nor charge-transfer complex fluorescence in supersonic
expansion but show exciplex fluorescence in solution.
Introduction
9-(p-N,N-(dimethylamino)phenylethyloxy)anthracene (1- and
9-An-O(CH2)2-DMA) and 1- and 9-(p-N,N-(dimethylamino)-
Jet-cooled intramolecular exciplex formation has been re-
ported in some bichromophoric electron donor-acceptor (EDA)
systems since pioneering works by Zewail and his co-workers.1,2
These intramolecular exciplexes are mostly limited to the
bichromophoric EDA systems with trimethylene except in only
a few cases.3 We reported several papers concerning with the
jet-cooled exciplex and excimer formations from van der Waals
(vdW) complexes.4,5 Similar jet-cooled exciplex formations of
vdW complexes were reported by other research groups.6-8
Furthermore, we reported the intramolecular exciplex in the
bichromophoric EDA system.9-12 In these inter- and intramo-
lecular exciplex formations, the excess vibrational energy
dependence for the exciplex formation is one of the most
interesting features in supersonic jet spectroscopy. Recently,
we have reported that multiconformations are involved in 1-(1-
and 9-anthryl)-3-(m-N,N-(dimethylamino)phenyl)propanes (ab-
breviated to 1- and 9-An-m-DMA) by hole-burning spectros-
copy.11 Furthermore, the vibrational energy thresholds for the
exciplex formations have been demonstrated to depend on the
ground-state conformations of these compounds.
On the other hand, the photochemistry in solutions, such as
that involved with the excimer/exciplex13 and biradical forma-
tions14,15 by a hydrogen atom transfer, have been investigated
in several bichromophoric systems with some ethereal chains,
for instance -O(CH2)nO- and -CH2OCH2-. Since the
synthesis of the ethereal bichromophoric chain compounds is
much easier than that of alkyl chain compounds, the ethereal
bichromophoric compounds were used sometimes for studies
of the intramolecular electronic interactions. In these ethereal
chain compounds, no significant difference from trimethylene
was observed in some cases of the photochemical behavior.
However, some new spectroscopic features in the ethereal
bichromophoric EDA systems different from those of the
trimethylene chain are expected in supersonic expansion.
This paper presents studies on the excited-state charge-transfer
interaction in ethereal bichromophoric EDA systems, 1- and
benzyloxy)methylanthracene (1- and 9-An-CH2OCH2-DMA),
in supersonic expansion. Intramolecular exciplex formation,
depending on excess vibrational energy, was observed in jet-
cooled 9-An-O(CH2)2-DMA, which is very similar to the
bichromophoric EDA systems with trimethylene. In 1-An-O-
(CH2)2-DMA, the existence of two isomeric forms was identified
by fluorescence excitation spectra. The visible fluorescence
excitation spectra of this compound show considerably broad
and blue-shifted vibrational structures, while the UV fluores-
cence excitation spectra show well-resolved vibrational struc-
tures. The excitation of the former band shows exciplex
fluorescence, which may be attributable to the excited-state
transformation of the van der Waals interaction between EDA
moieties in the ground state. The latter well-resolved UV
fluorescence excitation spectra suggest no exciplex fluorescence.
The other type of bichromophoric compounds, 1- and 9-An-
CH2OCH2-DMA, exhibit neither exciplex nor charge-transfer
complex fluorescence in supersonic expansion. The different
spectroscopic features between An-O(CH2)2-DMA and An-CH2-
OCH2-DMA were discussed in terms of fluorescence quenching
of the anthryl moieties by the ethereal oxygen atom of An-
CH2OCH2- and the intramolecular vibrational energy redistri-
bution in these compounds.
Experimental Section
Materials. Ethereal compound 1-An-O(CH2)2-DMA was
synthesized from 1-hydroxyanthracenes and p-(N,N-dimethy-
lamino)phenethyl tosylate. 1-Hydroxyanthracene was prepared
from 1-aminoanthracene (Nakarai Tesque) and sodium hydrox-
ysulfite by refluxing for 24 h in ethanol/water (1:2). p-(N,N-
Dimethylamino)phenethyl tosylate was synthesized from p-(N,N-
dimethylamino)phenethyl alcohol (Aldrich) and p-toluenesulfonyl
chloride in pyridine at <0 °C. 9-An-O(CH2)2-DMA was
synthesized from 9-anthrone/NaOH and p-(N,N-dimethylamino)-
phenethyl tosylate. 1- and 9-An-CH2OCH2-DMA were syn-
thesized from 1- and 9-anthryl methanol and p-(N,N-dimethy-
X Abstract published in AdVance ACS Abstracts, December 15, 1996.
S1089-5639(96)00950-4 CCC: $14.00 © 1997 American Chemical Society

32 J. Phys. Chem. A, Vol. 101, No. 1, 1997
Tsujiya et al.
Figure 1. Fluorescence excitation spectra monitored at (a) 400 and
(b) 460 nm of jet-cooled 9-An-O(CH2)2-DMA. (c) An UV fluorescence
excitation spectrum (400 nm) of 9-An-OCH2CH3 in similar supersonic
expansion.
Figure 2. Excess vibrational energy dependence of the dispersed
fluorescence spectra of 9-An-O(CH2)2-DMA.
lamino)benzyl bromide. These compounds were purified by
column chromatography (silica gel/dichloromethane/hexane) and
repeated recrystallization and further vacuum sublimation before
use. Structures and purities were confirmed by elementary
analysis and NMR (270 and 500 MHz) and mass spectroscopies.
1-An-O(CH2)2-DMA: mp 138-139 °C. Mass (m/z) 341 (M+).
Calcd for C24H23NO: C, 84.42; H, 6.79; N, 4.10. Found: C,
84.13; H, 6.72; N, 4.09. 9-An-O(CH2)2-DMA: mp 81-82 °C.
Mass (m/z) 341 (M+). Found: C, 84.23; H, 6.70; N, 4.12.
1-An-CH2OCH2-DMA: mp 126-127 °C. Mass (m/z) 341
(M+). Found: C, 84.32; H, 6.79; N, 4.00.
shows approximately a 1.9 nm red shift from that of the latter.
The low-frequency vibrations in 9-An-DMA were ascribed to
vibronic coupling of anthryl with methylene hydrogen atoms
of the center of trimethylene by Zewail and his co-workers, as
mentioned above. Figure 1 also shows the fluorescence
excitation spectrum of 9-An-OCH2CH3. The spectrum exhibits
an approximately 2.2 nm blue shift from that of 9-An-O(CH2)2-
DMA and lacks low-frequency vibration of 10-11 cm-1 and
29-30 cm-1 progressions. Therefore, the chain conformation
of 9-An-O(CH2)2-DMA seems considerably different from that
of 9-An-OCH2CH3. The UV fluorescence excitation spectra
of the former show a remarkable decrease in intensity with
increasing in vibrational energy, while the visible (460 nm)
fluorescence excitation spectra increase in intensity in the
vibronic band region with excess energy of >400 cm-1, as
shown in Figure 1. These fluorescence excitation spectra
suggest that this compound exhibits the intramolecular exciplex
fluorescence by the excitation of vibronic bands at approxi-
mately 400 cm-1 higher than the origin band. Figure 2 shows
the dispersed fluorescence spectra of this compound in a
supersonic expansion, which are remarkably dependent on the
excess vibrational energy. The dispersed fluorescence spectra
demonstrate that the jet-cooled exciplex in this ethereal com-
pound seems to be generated in the excess vibrational energy
threshold (∆E) lower than those in 9-An-DMA (900 cm-1) and
1-An-DMA (500 cm-1) with trimethylenes.1,2
Fluorescence decay times of the anthryl moiety of 9-An-
O(CH2)2-DMA were determined to be 16.4 ns in the origin band
excitation (376.72 nm) and 5 ns at 371.31 nm. Furthermore,
those were less than 1-2 ns in the excitations of higher vibronic
band regions. The anthryl fluorescence decay time (16.4 ns)
of the origin of this compound is similar to that (19.1 ns at the
origin) of a compound without the DMA moiety, 9-An-OCH2-
CH3. However, the decrease of decay times in the former was
more significant than that of the latter with increasing excess
vibrational energy. The exciplex fluorescence decay times
remarkably decrease with increasing excess vibrational energy
from 85 ns (at 371.31 nm, ∆E ) 387 cm-1) to 17 ns (at 358.0
nm, ∆E ) 1388 cm-1), though the exciplex decay times of
9-An-DMA with trimethylene were almost independent of
excess vibrational energy.10 These spectroscopic and decay
features of the ethereal compounds may be attributable to the
9-An-CH2OCH2-DMA: mp 124-127 °C. Mass (m/z) 341
(M+). Found: C, 84.40; H, 6.74; N, 4.15.
General Procedures. The experimental setup and procedures
of fluorescence spectroscopy of the pulsed supersonic free jet
were identical to those described in the previous papers.10,11
The 10 Hz pulsed supersonic free jet backed by He (two to
three atms) was excited at 10-12 mm downstream of a nozzle
by an excimer-laser-pumped dye laser (Lambda Physik Compex
102/FL 3002). The setup and procedures of the laser-induced
fluorescence spectra and decay were almost the same as
described previously.11,12 The spectra were detected through a
grating monochromator (Nikon G-250) by a photomultiplier
(Hamamatsu R1246). The spectral resolutions for the fluores-
cence excitation and for the dispersed fluorescence were
approximately 5 and 3 nm, respectively. The output signal was
processed by a boxcar integrator (SRS 250) and a personal
computer system. Fluorescence decay was determined by a
digital oscilloscope (Tektronix TDS 520) and processed by a
computer-simulated convolution.
Results
Fluorescence Spectroscopy of Jet-Cooled 9-An-O(CH2)2-
DMA. The UV fluorescence excitation spectrum of jet-cooled
9-An-O(CH2)2-DMA exhibits considerably resolved vibrational
structures starting with an origin band at 376.71 nm (26 545
cm-1), as shown in Figure 1. The vibrational structures with
low-frequency vibrations of 10-11 and 29-30 cm-1 were
observed in the origin band region. The former 10-11 cm-1
progressions are very similar to those of the UV fluorescence
excitation spectrum of 9-An-DMA extensively studied previ-
ously,1,2,10,16 though the spectrum of this ethereal compound

Bichromophoric EDA Systems
J. Phys. Chem. A, Vol. 101, No. 1, 1997 33
TABLE 1: Anthryl Fluorescence Decay Times in the
Origin Band Excitations of Ethereal Bichromophoric EDA
Systems in Comparison with Those of Similar Trimethylene
Systems10,16
origin band
nm (cm-1
decay time
ns
compound
)
9-An-CH2OCH2-DMA
9-An-CH2OCH3
9-An-(CH2)3-DMA (t)
(g)
1-An-CH2OCH2-DMA
9-An-O(CH2)2-DMA
9-An-OCH2CH3
370.29 (27 005)
370.39 (26 983)
374.77 (26 683)
(26 600-28 400)
363.72 (27 493)
376.71 (26 545)
374.52 (26 701)
374.74 (26 685)a
370.44 (26 995)b
368.70 (27 122)
(27 050-27 100)
9.6
8.3
19
9
7.4
19.1
16.4
14.0
<2
20
1-An-O(CH2)2-DMA
1-An-(CH2)3-DMA (t)
(g)
a An origin band of sharp vibrational structures exhibiting no
significant exciplex fluorescence. b An origin band of intramolecular
vdW state exhibiting exciplex fluorescence.
Figure 4. Dispersed fluorescence spectra excited at (a) 370.70 nm
(26 976 cm-1), (b) 359.40 nm (27 824 cm-1), and (c) 355.10 nm
(281 612 cm-1). The excitation bands are indicated by arrows in Figure
3.
system of anthracene and N,N-dimethylaniline (DMA). The
fluorescence excitation spectrum looks like a superposition of
a broad and diffuse band system and the closely spaced narrow
band system. The origin bands of the former and latter band
systems were red-shifted approximately 403 and 525 cm-1 from
that of anthracene, respectively. Furthermore, they reported that
the narrow band excitations exhibit vibrationally resolved
fluorescence of the complex, while the broad band excitation
does the exciplex fluorescence at 420-480 nm.7 On the other
hand, Kizu and Itoh9 reported the jet-cooled exciplex fluores-
cence from the van der Waals (vdW) complex between 9,10-
dicyanoanthracene and naphthalene. This jet-cooled system
showed a rather broad fluorescence excitation spectrum whose
intensity was dependent on the vapor pressure of naphthalene.
In the 1-An-O(CH2)2-DMA system, the shape and relative
intensity of the broad bands shown in Figure 3b were indepen-
dent of vapor pressure of the sample variable with nozzle
temperature. Therefore, these broad bands may be attributable
to the intramolecular interaction between bichromophoric EDA
moieties of 1-An-O(CH2)2-DMA. Furthermore, taking account
the existence of two isomeric forms involved in the jet-cooled
intermolecular anthracene/DMA system,7 the vibrationally
resolved structures in the UV fluorescence excitation spectrum
and the broad congested bands in the visible one (Figure 3)
were tentatively ascribed to open and closed forms of the
ethereal chain system, respectively. If there is a strong charge-
transfer interaction between EDA moieties in the ground state
of the closed form, the visible fluorescence excitation spectrum
may be very broad bands without vibrational structures.
Therefore, the considerably congested vibrational structures in
the visible fluorescence excitation spectrum shown in Figure
3b suggests a weak van der Waals interaction between EDA
moieties in the closed form of this ethereal chain compound.
Anthryl fluorescence decay times were obtained to be 14.0
ns in the sharp origin band excitation and considerably decreased
in the excess vibrational energy region (for instance 9.3 ns at
∆E ) 1396 cm-1). However, the excess energy dependence
of the anthryl decay time of this compound was not so
remarkable as that of 9-An-O(CH2)2-DMA, which means there
is no significant exciplex formation in this open form as
Figure 3. Fluorescence excitation spectra monitored at (a) 397.5 and
(b) 460 nm of 1-An-O(CH2)2-DMA in supersonic expansion.
intramolecular interaction between anthryl and oxygen atom,
as will be mentioned later. These fluorescence decay times are
summarized in Table 1.
Fluorescence Spectroscopy of Jet-Cooled 1-An-O(CH2)2-
DMA. Figure 3 shows fluorescence excitation spectra of 1-An-
O(CH2)2-DMA in a supersonic expansion. The origin band at
374.74 nm (26 685 cm-1) of the UV fluorescence excitation
spectrum exhibits a remarkable red shift from that of the
corresponding bichromophoric compound 1-An-DMA with
trimethylene (368.70 nm, 27 122 cm-1). However, no signifi-
cant low-frequency vibration was observed in the origin band
region of this ethereal compound. The vibrational structures
of the UV fluorescence excitation spectrum are very similar to
that of anthracene (an origin, 27 695 cm-1) except for a large
red shift from the latter. The visible (460 nm) fluorescence
excitation spectrum of 1-An-O(CH2)2-DMA shows very broad
congested bands, which are blue-shifted approximately 4.3 nm
from the sharp origin and the respective vibronic bands of the
UV fluorescence excitation spectrum, as shown in Figure 3. It
is noteworthy that no sharp vibronic bands were observed in
addition to the broad bands in the visible fluorescence excitation
spectra. The fact suggests that the excitation of the sharp
vibronic bands exhibits no exciplex fluorescence, while the
broad band excitations reveal the visible fluorescence, probably
the exciplex fluorescence. Dispersed fluorescence spectra
obtained by the typical sharp and broad band excitations are
shown in Figure 4. Castella, Tramer, and Piuzzi7 reported the
existence of two isomeric forms in the jet-cooled intermolecular

34 J. Phys. Chem. A, Vol. 101, No. 1, 1997
Tsujiya et al.
Figure 5. Fluorescence excitation spectra of (a) 9-An-CH2OCH2-DMA
and (b) 9-An-CH2OCH3 in supersonic expansion. (c) A fluorescence
excitation spectrum of 1-An-CH2OCH2-DMA. Fluorescence was
detected at 392 nm in (a) and (b) and at 384 nm in (c).
mentioned above. On the other hand, the UV fluorescence
decay times were less than 2 ns in excitations of the broad vdW
bands of the closed form even in the origin band region. The
facts suggest that the visible fluorescence, probably exciplex,
may be generated by the excited-state transformation of the
intramolecular vdW state (the closed form) of this compound.
These fluorescence spectral and decay features are consistent
with the assignments that the sharp and broad bands shown in
Figure 3 were attributable to the open and closed forms,
respectively. However, the actual structures of these ethereal
chain conformations and the possibility of the exciplex formation
from the open form in the higher vibronic band region are not
obvious at the present stage.
Figure 6. (a) Excess vibrational energy (∆E/cm-1) dependence of
dispersed fluorescence spectra of 9-An-CH2OCH2-DMA in supersonic
jet. (b) Fluorescence spectrum of this compound in a deaerated
3-methylpentane solution (excitation wavelength, 365 nm) at room
temperature.
Fluorescence Spectroscopy of Jet-Cooled 1- and 9-An-
CH2OCH2-DMA. Figure 5 shows UV fluorescence excitation
spectra of 1- and 9-An-CH2OCH2-DMA monitored at 392 nm
and that of a model compound, 9-An-CH2OCH3 (392 nm), in a
supersonic expansion. The fluorescence excitation spectra
detected at 440 nm of two former compounds exhibit almost
identical vibrational structures and relative intensities with their
respective UV fluorescence excitation spectra. Figure 6 shows
typical dispersed fluorescence spectra of 9-An-CH2OCH2-DMA
in excitations of an origin and several vibronic bands. These
fluorescence excitation and dispersed fluorescence spectra
indicate that no exciplex fluorescence was detected in these jet-
cooled compounds, though these compounds exhibit exciplex
fluorescence in polar and nonpolar solutions. A typical exciplex
fluorescence spectrum of 9-An-CH2OCH2-DMA in a deaerated
3-methylpentane solution is shown in Figure 6b.
As shown in Figure 5, the excitation spectra of 9-An-CH2-
OCH2-DMA and 9-An-CH2OCH3 exhibit almost identical
vibrational structures, and their origins are very much red-shifted
(490-510 cm-1) from that of 1-An-CH2OCH2-DMA. The
comparison of excitation spectra between the 9-An-CH2OCH2-
DMA and 9-An-CH2OCH3 indicates no significant intramo-
lecular interaction between anthryl and DMA moieties in the
former. The facts may be confirmed from the excess vibrational
energy dependence of the anthryl fluorescence decay times, as
will be mentioned later. Fluorescence decay times (decay rate
constants) of these ethereal compounds were measured in the
excitations of the origin and major vibronic bands. Figure 7
illustrates the excess energy dependence of fluorescence decay
rate constants of the ethereal compounds in comparison with
Figure 7. Plots of decay rate constants of anthryl fluorescence vs
excess vibrational energies (∆E) of four jet-cooled compounds indicated
in figure. Errors of decay rate constants are approximately <10%.
those of 9-An-OCH2CH3. The fluorescence decay rate constants
of 9-An-CH2OCH2-DMA and 9-An-CH2OCH3 show very
similar excess energy dependence throughout ∆E ) 0-1400
cm-1. In 1-An-CH2OCH2-DMA, the UV fluorescence excita-
tion spectrum exhibits a considerable blue shift from those of
the former as mentioned above. Furthermore, anthryl decay
rate constants remarkably increase with increasing excess
vibrational energy. The fact suggests a considerable fluores-
cence quenching of the 1-anthryl group in the higher vibronic

Bichromophoric EDA Systems
J. Phys. Chem. A, Vol. 101, No. 1, 1997 35
band region, though no significant exciplex fluorescence was
observed, as mentioned above. However, it is not obvious why
1-anthryl fluorescence is more quenched than 9-anthryl in these
ethereal chain molecules at the present stage.
anthryl moiety does not seem so significant in the low
vibrational energy region of this compound. These spectral
features are almost similar to those of 9-An-DMA. In 1-An-
O(CH2)2-DMA, however, two isomeric forms are involved, as
mentioned in the last section. One of them exhibits rather
diffuse fluorescence excitation spectra and exciplex fluorescence
by the excited-state transformation of the intramolecularly
interacting state, which was ascribed to the van der Waals
interaction between two moieties. The vdW state may be
tentatively ascribed to the intramolecularly closed form. An-
other isomer shows no significant exciplex fluorescence in the
excess energy region of <1300 cm-1. In the higher vibronic
band regions, no significant difference between two isomeric
forms can be distinguished for the exciplex formation. Taking
account of the 14-15 ns of anthryl decay time of the origin
band in this isomer, there seems to be only small intramolecular
interaction between the two moieties, which may be a possible
open form.
Discussion
Hopkins et al.17 reported the rotational isomers of trans and
gauche conformations in jet-cooled propylbenzene. The rate
constant of the intramolecular vibrational energy redistribution
(IVR) was suggested to be much smaller in the gauche
conformer (g) than the trans one (t) in propylbenzene.18 At a
low He backing pressure of the supersonic expansion, the similar
gauche and trans conformers were reported in the trimethylene
bichromophoric compounds, 1-(1- and 9-anthryl)-3-phenylpro-
panes (1- and 9-An-Ph) and also in 1- and 9-An-DMA. The
gauche conformers of 1- and 9-An-DMA were reported to
exhibit no significant exciplex fluorescence. The fluorescence
decay times of the origin bands of the gauche conformer of
9-An-Ph and 9-An-DMA were approximately 9 ns, while those
of the trans were 19-20 ns. The smaller decay times of the
gauche were ascribed to a considerable fluorescence quenching
of the anthryl moiety in the origin band region. These features
of the gauche conformers in 1- and 9-An-DMA were ascribed
to the smaller IVR rate constant than those of the trans ones.
In the gauche form, the anthryl vibrational energy transfer to
the trimethylene leading to the favorable conformation in the
exciplex was suggested to be prevented. The smaller possibility
of IVR in this conformer of the trimethylene was reported to
be responsible for no significant exciplex formation in the
gauche conformer of 1- and 9-An-DMA in the previous
paper.10,16
Acknowledgment. This work was supported by a Grant-
in-Aid on Priority-Area-Research “Photoreaction Dynamics”
(No. 06239103) from the Ministry of Education, Science, Sports,
and Culture of Japan. The authors are indebted to Dr. T.
Shinoda, Faculty of Pharmaceutical Sciences, Toyama Medical
and Pharmaceutical University, for his kind AM1 calculations
of geometrical optimization of molecules.
References and Notes
(1) Felker, P. M.; Syage, J. A.; Lambert, W. R.; Zewail, A. M. Chem.
Phys. Lett. 1982, 92, 1.
(2) Syage, J. A.; Felker, P. M.; Zewail, A. M. J. Chem. Phys. 1984,
81, 2233.
In jet-cooled 1- and 9-An-CH2OCH2-DMA, anthryl fluores-
cence decay times of the origin band region are 7.4 and 9.6 ns,
respectively, as mentioned in the last section (Table 1). These
decay times are considerably shorter than those of 9-An-OCH2-
CH3 (16.4 ns) and 9-An-O(CH2)2-DMA (19.1 ns). The short
decay times of the anthryl in 1- and 9-An-CH2OCH2-DMA seem
to suggest a weak intramolecular interaction between an ethereal
oxygen atom of -CH2OCH2- and the anthryl moiety. It is
likely that the intramolecular interaction between the ethereal
oxygen and the anthryl moiety is attributable to a weak charge-
transfer character induced by the nonbonding electrons on the
oxygen atom to the anthryl in these compounds. This intramo-
lecular interaction leads to a rigid chain conformation of these
-CH2OCH2- bichromophoric compounds. Preliminary results
of AM-1 semiempirical calculations of the ethereal chain
conformation suggest that the rigid conformation is similar to
the gauche conformation of the trimethylene.19 By analogy to
the spectral and IVR features in the methylene gauche conformer
in 1- and 9-An-DMA, the smaller possibility of anthryl
vibrational energy transfer to the rigid ethereal chains, leading
to the favorable chain transformation for the exciplex, seems
to be responsible for no exciplex formation and small anthryl
decay times in 1- and 9-An-CH2OCH2-DMA (7.4 and 9.6 ns at
the origin), as mentioned above.
As mentioned in the last section, the exciplex fluorescence
decay time in 9-AnO(CH2)2-DMA was observed in the excess
vibrational energy of >400 cm-1. The anthryl decay time of
19.1 ns in the origin band region remarkably decreased with
increasing excess vibrational energy, whose decrement of the
decay times in the higher vibronic region may be attributable
to the increase of rate constants of the exciplex formation as
well as to the nonradiative process. Taking into account the
anthryl decay time of the origin region, the intramolecular
interaction between the oxygen atom of -O(CH2)2- and the
(3) (a) Wegewijs, G.; Hermant, R. M.; Verhoven, J. W.; Kunst, A. G.
M.; Rettschnick, R. P. H. Chem. Phys. Lett. 1987, 140, 567. (b) Shou, H.;
Alfano, J. C.; van Dantzig, N. A.; Levy, D. H. J. Chem. Phys. 1991, 95,
711. (c) van Dantzig, N. A.; Shou, H.; Alfano, J. C.; Yang, N. C.; Levy,
D. H. J. Chem. Phys. 1994, 100, 7068.
(4) (a) Saigusa, H.; Itoh, M. Chem. Phys. Lett. 1984, 106, 391; J. Chem.
Phys. 1984, 81, 5682. (b) Saigusa, H.; Itoh, M.; Baba, H.; Hanazaki, I. J.
Chem. Phys. 1987, 86, 2529. (c) Itoh, M.; Morita, Y. J. Phys. Chem. 1988,
92, 5693, and references cited therein.
(5) Itoh, M.; Sasaki, M. J. Phys. Chem. 1990, 94, 6544.
(6) Castella, M.; Prochorow, M.; Tramer, A. J. Chem. Phys. 1984, 81,
2511.
(7) Castella, M.; Tramer, A.; Piuzzi, F. Chem. Phys. Lett. 1986, 129,
112.
(8) Anner, O.; Haas, Y. J. Am. Chem. Soc. 1988, 110, 1416, and
references cited therein.
(9) Kizu, N.; Itoh, M. J. Phys. Chem. 1990, 96, 5796.
(10) Kizu, N.; Itoh, M. J. Am. Chem. Soc. 1993, 115, 4799.
(11) (a) Kurono, M.; Takasu, R.; Itoh, M. J. Phys. Chem. 1994, 98,
5925. (b) Kurono, M.; Takasu, R.; Itoh, M. J. Phys. Chem. 1995, 99, 9668.
(12) Kurono, M.; Itoh, M. J. Phys. Chem. 1995, 99, 17113.
(13) (a) Wang, Y. C.; Morawetz, H. J. Am. Chem. Soc. 1976, 98, 3611.
(b) Mugnier, J.; Valeur, B.; Gratton, E. Chem. Phys. Lett. 1985, 119, 217.
(14) Tanimoto, Y.; Kita, A.; Itoh, M.; Okazaki, M.; Nakagaki, R.;
Nagakura, S. Chem. Phys. Lett. 1990, 165, 184.
(15) (a) Tanimoto, Y.; Okada, N.; Takamatsu, S.; Itoh, M. Bull. Chem.
Soc. Jpn. 1990, 63, 1342. (b) Tanimoto, Y.; Nagano, M.; Fujiwara, Y.;
Kohtani, S.; Itoh, M. J. Photochem. Photobiol. A 1993, 74, 153.
(16) Takasu, R.; Kizu, N.; Itoh, M.; Shinoda, H. J. Chem. Phys. 1994,
101, 7364.
(17) (a) Hopkins, J. B.; Powers, D. E.; Mukamel, S.; Smalley, K. E. J.
Chem. Phys. 1980, 72, 5049. (b) Hopkins, J. B.; Powers, D. E.; Mukamel,
S.; Smalley, R. E. J. Chem. Phys. 1980, 77, 5049.
(18) Syage, J. A.; Felker, P. M.; Semmes, D. H.; Zewail, A. H. J. Chem.
Phys. 1985, 82, 2896.
(19) Private communication from Dr. H. Shinoda, Toyama Medical and
Pharmaceutical University, which will be submitted elsewhere. The AM-1
calculations were carried out by the same method as reported in ref 16.