“…More specifically, the rapid bimolecular decay at early times is followed by a slower unimolecular decay at later times. As expected from the work on naphthalenophanes, the benzophenone-sensitized transient absorption of naphthalene solutions exhibits no spectral feature due to the ketyl radical. 1 Benzophenone-sensitized transient absorption spectrum of a 3 M solution of naphthalene in toluene at room temperature.…”
Section: Resultssupporting
confidence: 65%
“…The advantage of using benzophenone in the triplet sensitization of naphthalene is that the transient absorption spectrum of triplet benzophenone as well as that of the ketyl radical are well characterized, and there is no evidence for the formation of a complex or an exciplex between benzophenone and naphthalene. Experiments of Shizuka and co-workers on triplet sensitization of naphthalenophanes demonstrate that the ketyl radical (λ obs = 545 nm) is not produced even under high-power (40 mJ/pulse) excitation of benzophenone by the third harmonic (355 nm) of a Nd:YAG laser. In our experiments, approximately 10 -2 M of benzophenone in 1−4 M solutions of naphthalene were excited with about 25 mJ/pulse of the 355 nm Nd:YAG laser beam.…”
We report here the observation of the laser-induced transient absorption spectrum of intermolecular triplet
excimers of naphthalene in fluid solution. This assignment is confirmed by comparison to the transient
absorption spectra of the intramolecular triplet excimers of covalently linked dimers of naphthalene and
quinoxaline.
“…More specifically, the rapid bimolecular decay at early times is followed by a slower unimolecular decay at later times. As expected from the work on naphthalenophanes, the benzophenone-sensitized transient absorption of naphthalene solutions exhibits no spectral feature due to the ketyl radical. 1 Benzophenone-sensitized transient absorption spectrum of a 3 M solution of naphthalene in toluene at room temperature.…”
Section: Resultssupporting
confidence: 65%
“…The advantage of using benzophenone in the triplet sensitization of naphthalene is that the transient absorption spectrum of triplet benzophenone as well as that of the ketyl radical are well characterized, and there is no evidence for the formation of a complex or an exciplex between benzophenone and naphthalene. Experiments of Shizuka and co-workers on triplet sensitization of naphthalenophanes demonstrate that the ketyl radical (λ obs = 545 nm) is not produced even under high-power (40 mJ/pulse) excitation of benzophenone by the third harmonic (355 nm) of a Nd:YAG laser. In our experiments, approximately 10 -2 M of benzophenone in 1−4 M solutions of naphthalene were excited with about 25 mJ/pulse of the 355 nm Nd:YAG laser beam.…”
We report here the observation of the laser-induced transient absorption spectrum of intermolecular triplet
excimers of naphthalene in fluid solution. This assignment is confirmed by comparison to the transient
absorption spectra of the intramolecular triplet excimers of covalently linked dimers of naphthalene and
quinoxaline.
“…For each dimer, the LE and CT absorption systems decay with rates which are identical to each other, and to the decay rate of the respective phosphorescence. 23 The intermoiety CT absorption has also been observed for dinaphthylmethanes, 10 dinaphthyl ethers, 10 naphthalene-annelated dimers, 13 quinoxaline-annelated dimer, 13 naphthalenophans, 24 and the sandwich dimer of naphthalene. 23 We may therefore conclude that, the transient absorption spectra reveal the intermoiety interaction leading to the stabilization of triplet excimer, even for systems that exhibit monomeric phosphorescence.…”
Time-resolved EPR (TREPR), transient absorption, and phosphorescence spectra have been measured in solid
matrixes at 77 K for the covalently linked L-shaped dimers of naphthalene, in which the in-plane long axes
of the two naphthalene moieties are parallel and the in-plane short axes make an angle. The zero-field splitting
(ZFS) parameters obtained by simulation of the TREPR spectra are consistent with the dimer geometries, if
it is assumed that excitation exchange interaction is responsible for the small D values of the dimers relative
to the monomer. The tilt angle in the triplet state is significantly smaller for the dimers exhibiting excimeric
phosphorescence than those exhibiting monomeric emission. Comparison of the spectral position and lifetime
of phosphorescence from the L-shaped dimers with those from the sandwich dimers indicates that the excitation
exchange interaction is substantially greater for the L-shaped dimers as compared to the sandwich dimers.
The proposal that the preferred conformation of the triplet excimer of naphthalene is L-shaped, rather than
sandwich, is supported by the measurements.
“…In this context, we have synthesized and subjected cyclophanes having two aromatic chromophores linked with two oligomethylene chains to study the deactivation processes in the photoexcited singlet and triplet states by emission and transient absorption measurements. [61][62][63] We have been investigating photochemical reactions of cyclophanes tethering two benzene rings with various numbers of the oligomethylene chain, -(CH 2 ) 3 -that enables to keep the chromophores parallel (Scheme 1). 64-68 4 In the present study, we have performed spectroscopic investigations of 3nCPs by measurements of emission and transient absorption, and revealed the photophysical properties of singlet and triplet excimeric states.…”
Section: Introductionmentioning
confidence: 99%
“…To understand the nature of triplet excimer, it is desirable to simultaneously elucidate both the emission and absorption by using well-designed molecular systems. In this context, we have synthesized and subjected cyclophanes having two aromatic chromophores linked with two oligomethylene chains to study the deactivation processes in the photoexcited singlet and triplet states by emission and transient absorption measurements. − We have been investigating photochemical reactions of cyclophanes tethering two benzene rings with various numbers of the oligomethylene chain, −(CH 2 ) 3 – that enables us to keep the chromophores parallel (Scheme ). − …”
Photophysical and photochemical features of [3n]cyclophanes (3nCPs) (n = 2-6) in solution were investigated by emission and transient absorption measurements. The studied 3nCPs show excimer fluorescence without locally excited fluorescence whereas some of them emit excimer phosphorescence in rigid glass at 77 K. The probability of excimeric phosphorescence from transannular π-electron systems was shown to strictly depend on the symmetric molecular structures. A feature of intersystem crossing from an excimeric fluorescence state to the excimeric triplet state was observed. Transient absorption spectra obtained upon laser flash photolysis of 3nCP revealed formation of the triplet excimer states. Triplet sensitization of 33CP using xanthone as the sensitizer demonstrated formation of triplet 33CP via triplet energy transfer whereas from the xanthone ketyl radical formation, it was inferred that triplet xanthone undergoes H atom abstraction from 32CP, providing a benzylic 32CP radical as the counter species. Based on kinetic and spectroscopic data obtained upon laser flash photolysis, differences in photochemical reactions of triplet xanthone between 32CP and 33CP were discussed.
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