Ordering, Interaction, and Reactivity of the Low‐Lying nπ* and ππ* Excited Triplet States of Acetophenone Derivatives

Yabumoto, Sohshi; Shigeto, Shinsuke; Lee, Yuan‐Pern; Hamaguchi, Hiro O.

doi:10.1002/anie.201004571

Cited by 22 publications

(26 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In all the solvents studied, the transient NIR spectra of the three compounds exhibit two broad electronic bands with various intensities that are assigned to triplet-triplet transitions from the lowest nπ* and ππ* states. As in our previous experiments in benzene, 29 those bands decay in unison. This finding indicates that the thermal equilibrium between the T 1 and T 2 states of the AP derivatives exists irrespective of the solvents used.…”

mentioning

confidence: 68%

“…The lower wavenumber band is assigned to a triplet-triplet transition from the nπ* state (T nπ* band) and the higher wavenumber to that from the ππ* state (T ππ* band). 29 As is evident from Figure 1, the T nπ* and T ππ* bands decay synchronously in all the solvents studied. Previously we observed a similar synchronous decay of the two transient electronic bands of AP in benzene and interpreted it as being due to the thermal equilibrium between the nπ* and ππ* states that are the initial states for the T nπ* and T ππ* transitions.…”

Section: Acs Paragon Plus Environmentmentioning

confidence: 80%

“…The apparatus used for nanosecond timeresolved NIR spectroscopy has been described previously. 29,33,34 It employs a dispersive monochromator in combination with alternating current (AC)-coupled detection. 35,36 The ACcoupled technique enables us to detect absorbance difference as small as 1 × 10 −6 .…”

Section: Methodsmentioning

confidence: 99%

“…23,24 Recently we have provided a conclusive picture of the ordering of the low-lying excited triplet states and its substituent dependence in four AP derivatives (AP, CF 3 -AP, Me-AP, and 4′-methoxyacetophenone (MeO-AP)) using nanosecond time-resolved near-IR (NIR) spectroscopy. 29 We found that the photoreduction activity of the AP derivatives correlates well with the intensity ratio of NIR electronic bands that correspond to nπ* ← nπ* and ππ* ← ππ* transitions, and that the low-lying nπ* and ππ* triplet states of AP, Me-AP, and MeO-AP are in thermal equilibrium. We confirmed the thermal equilibrium by measuring the temperature effect on the band intensity ratio in α,α,α-trifluorotoluene solution.…”

mentioning

confidence: 93%

See 3 more Smart Citations

Direct Observation of the Solvent Effects on the Low-Lying nπ* and ππ* Excited Triplet States of Acetophenone Derivatives in Thermal Equilibrium

Narra¹,

Shigeto

2015

J. Phys. Chem. B

Self Cite

View full text Add to dashboard Cite

Low-lying excited triplet states of aromatic carbonyl compounds exhibit diverse photophysical and photochemical properties of fundamental importance. Despite tremendous effort in studying those triplet states, the effects of substituents and solvents on the energetics of the triplet manifold and on photoreactivity remain to be fully understood. We have recently studied the ordering of the low-lying nπ* and ππ* excited triplet states and its substituent dependence in acetophenone derivatives using nanosecond time-resolved near-IR (NIR) spectroscopy. Here we address the other important issue, the solvent effects, by directly observing the electronic bands in the NIR that originate from the lowest nπ* and ππ* states of acetophenone derivatives in four solvents of different polarity (n-heptane, benzene, acetonitrile, and methanol). The two transient NIR bands decay synchronously in all the solvents, indicating that the lowest nπ* and ππ* states are in thermal equilibrium irrespective of the solvent polarity studied here. We found that the ππ* band increases in intensity relative to the nπ* band as solvent polarity increases. These results are compared with the photoreduction rate constant for the acetophenone derivatives in the solvents to which 2-propanol was added as a hydrogen-atom donor. Based on the present findings, we present a comprehensive, solvent- and substituent-dependent energy level diagram of the low-lying nπ* and ππ* excited triplet states.

show abstract

mentioning

confidence: 68%

Section: Acs Paragon Plus Environmentmentioning

confidence: 80%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 93%

See 2 more Smart Citations

Direct Observation of the Solvent Effects on the Low-Lying nπ* and ππ* Excited Triplet States of Acetophenone Derivatives in Thermal Equilibrium

Narra¹,

Shigeto

2015

J. Phys. Chem. B

Self Cite

View full text Add to dashboard Cite

show abstract

“…20,21 Briefly, sample solutions were photoexcited by the third harmonic of a pulsed Q-switched Nd:YAG laser (IB LASER DiNY pQ355, 355 nm, 250 Hz, 40¯J/pulse, 7 ns) or by the second harmonic of a DCM dye laser (345 nm). Probe radiation in the IR region from a ceramic infrared light emitter (JASCO) was focused onto sample solution.…”

mentioning

confidence: 99%

Nanosecond Time-resolved Infrared Spectra and Structure of the Charge-transfer State of 9,9′-Bianthryl in Acetonitrile

Asami

Yabumoto

Shigeto³

et al. 2012

Chemistry Letters

Self Cite

View full text Add to dashboard Cite

Nanosecond time-resolved infrared spectra of photoexcited 9,9¤-bianthryl (BA) and its deuterated derivative ) were recorded in acetonitrile-d 3 and cyclohexane-d 12 . The chargetransfer (CT) bands observed at the 12001400 cm ¹1 region are contributed mostly by the intra-and inter-ring CC stretch vibrations. The intrinsic frequency of the inter-ring CC stretch falls within the 12001400 cm ¹1 region, which is consistent more with a twisted structure than with a fully conjugated planar structure of the CT state.Photoinduced charge transfer (CT) is a fundamental chemical reaction. The intramolecular CT state formation in 9,9¤-bianthryl (BA) has attracted attention since its proposal in 1968. 1A large number of spectroscopic experiments on the CT reaction in BA have been performed in the UVvisible region in clusters, 24 in solutions, 512 or in ionic liquids. 13,14 When BA is irradiated by UV light, it is excited to the locally excited (LE) state in which one of the anthracene moieties is electronically excited. The CT reaction proceeds between the two anthracene moieties after the UV irradiation in polar solvents, while it is widely accepted that the complete CT reaction does not proceed in nonpolar solvents. Our previous time-resolved near-IR absorption experiments 1518 have revealed that an intermediate, "partial CT (PCT)" state, is formed in the CT reaction. The PCT state has a transition dipole moment parallel to the inter-ring CC bond as the CT state does. 17 The PCT state is also observed in nonpolar solvents, where it is in equilibrium with the LE state. 17,18 Structural information on BA in the CT and PCT states is required for elucidating the detailed mechanism of the CT reaction. Internal rotation is proposed as one of the key factors that determine the reaction kinetics. The internal rotation process around the central CC bond is presumable, because a nonperpendicular dihedral angle is favorable for effective inter-ring interaction. For examining the molecular structure of BA in the CT and PCT states, time-resolved IR and Raman spectroscopy is an effective method, because the internal rotation will affect the position and the strength of the inter-ring CC stretch band. To the best of our knowledge, however, there has been no study reported on time-resolved vibrational spectroscopy of the excited state of BA in solution, except for a time-resolved CARS/CSRS experiment. 19 The CSRS signals of BA in the CT state were all assigned to ring vibrations, whereas no vibrational band predominated by the inter-ring CC stretch was reported. In this letter, nanosecond time-resolved IR spectra of BA and its deuterated derivative, BA-d 18 , are reported. We assign the observed spectra to the CT state of BA and discuss the origin of the IR bands.Transient absorption spectra were measured with a nanosecond time-resolved IR absorption spectrometer. 20,21 Briefly, sample solutions were photoexcited by the third harmonic of a pulsed Q-switched Nd:YAG laser (IB LASER DiNY pQ355, 355 nm, 250 Hz, 40¯J/pulse, 7 ns) or by the se...

show abstract

Is Our Way of Thinking about Excited States Correct? Time‐Resolved Dispersive IR Study on p‐Nitroaniline

Narra¹,

Chang²,

Witek³

et al. 2012

Chemistry A European J

Self Cite

View full text Add to dashboard Cite

Low-lying excited electronic states of an important class of molecules known as push-pull chromophores are central to understanding their potential nonlinear optical properties. Here we report that a combination of high-sensitivity nanosecond time-resolved dispersive IR spectroscopy and DFT calculations on p-nitroaniline (PNA), a prototypical push-pull molecule, reveals that PNA in the lowest excited triplet state has a partial quinoid structure. In this structure, the quinoid configuration is restricted to a part of the phenyl ring adjacent to the NO(2) group. The partial quinoid structure of PNA cannot be explained by a commonly used hybrid of a neutral form and a zwitterionic charge-transfer form. Our findings not only cast doubt on the general applicability of the classical way of looking at excited states, based exclusively on characteristic resonance structures, but also provide deeper insights into excited-state structure of highly polarizable molecular systems.

show abstract

Ordering, Interaction, and Reactivity of the Low‐Lying nπ* and ππ* Excited Triplet States of Acetophenone Derivatives

Cited by 22 publications

References 22 publications

Direct Observation of the Solvent Effects on the Low-Lying nπ* and ππ* Excited Triplet States of Acetophenone Derivatives in Thermal Equilibrium

Direct Observation of the Solvent Effects on the Low-Lying nπ* and ππ* Excited Triplet States of Acetophenone Derivatives in Thermal Equilibrium

Nanosecond Time-resolved Infrared Spectra and Structure of the Charge-transfer State of 9,9′-Bianthryl in Acetonitrile

Is Our Way of Thinking about Excited States Correct? Time‐Resolved Dispersive IR Study on p‐Nitroaniline

Contact Info

Product

Resources

About