“…We therefore assign this value to the singlet state lifetime. Similar values have been observed for the singlets of other aromatic ketones (48–50). The insensitivity of the lifetime to solvent is consistent with the solvent independence of the triplet quantum yield of PN (10, 11).…”
Section: Resultssupporting
confidence: 85%
“…We rule out this species as an upper singlet excited state because it did not disappear when it was irradiated at 400 nm. We did not attempt to further investigate its nature, though we note that similar behavior is found in phenyl‐substituted benzophenones and is explained in terms of conformational changes of the phenyl ring in the first excited singlet state (50).…”
Experiments were performed to elucidate the excited-state behavior of 9-phenylphenalenones, which are phototoxic plant secondary metabolites involved in mechanisms of light-mediated plant defense. Using a combination of time-resolved and steady-state UV/visible spectroscopies, time-resolved IR absorption spectroscopy, time-resolved singlet oxygen phosphorescence measurements and cyclic voltammetry, we provide evidence of an intramolecular charge-transfer process in the excited singlet and the triplet states of 9-phenylphenalenones that modulates the photosensitized production of singlet oxygen.
“…We therefore assign this value to the singlet state lifetime. Similar values have been observed for the singlets of other aromatic ketones (48–50). The insensitivity of the lifetime to solvent is consistent with the solvent independence of the triplet quantum yield of PN (10, 11).…”
Section: Resultssupporting
confidence: 85%
“…We rule out this species as an upper singlet excited state because it did not disappear when it was irradiated at 400 nm. We did not attempt to further investigate its nature, though we note that similar behavior is found in phenyl‐substituted benzophenones and is explained in terms of conformational changes of the phenyl ring in the first excited singlet state (50).…”
Experiments were performed to elucidate the excited-state behavior of 9-phenylphenalenones, which are phototoxic plant secondary metabolites involved in mechanisms of light-mediated plant defense. Using a combination of time-resolved and steady-state UV/visible spectroscopies, time-resolved IR absorption spectroscopy, time-resolved singlet oxygen phosphorescence measurements and cyclic voltammetry, we provide evidence of an intramolecular charge-transfer process in the excited singlet and the triplet states of 9-phenylphenalenones that modulates the photosensitized production of singlet oxygen.
“…Curves a and b in Figure B and C show the transient absorption spectra obtained by flash photolysis of p -HOBP and BP in acetonitrile upon excitation with 310-nm laser pulses of subpicosecond duration and recorded at 1 and 660 ps after the laser pulse, respectively. Curves a and b can be assigned to the S 1 and T 1 states of p -ABP, respectively. ,, The lifetime of the growth of the T 1 state has been determined to be 3.5 ± 0.2 ps for p -HOBP in acetonitrile, and those for BP have been reported earlier to be 9 ps in acetonitrile, , 10 ps in benzene, and 14 ps in ethanol. ,, Hence, a comparison between the spectral and decay characteristics of the S 1 and T 1 states produced by photolysis of BP, p -HOBP, and p -ABP in acetonitrile shows a clear difference between those of p -ABP and those of the other two. 5 Absorption spectra of the transients recorded at (a) 1 ps and (b) 660 ps after the photolysis of (A) p -ABP, (B) p -HOBP, and (C) BP in acetonitrile by subpicosecond laser pulses of 310 nm.…”
Section: Resultsmentioning
confidence: 90%
“…1,2,11 The lifetime of the growth of the T 1 state has been determined to be 3.5 ( 0.2 ps for p-HOBP in acetonitrile, and those for BP have been reported earlier to be 9 ps in acetonitrile, 2,28 10 ps in benzene, and 14 ps in ethanol. 2,29,30 Hence, a comparison between the spectral and decay characteristics of the S 1 and T 1 states produced by photolysis of BP, p-HOBP, and p-ABP in acetonitrile shows a clear difference between those of p-ABP and those of the other two.…”
The photophysical properties of the singlet (S 1 ) and triplet (T 1 ) excited states of p-aminobenzophenone (p-ABP) have been investigated in various organic solvents using steady-state as well as transient absorption spectroscopy with picosecond and subpicosecond time resolution. p-ABP is weakly fluorescent in benzene as well as in polar aprotic solvents, acetonitrile, DMSO, and DMF, but nearly nonfluorescent in cyclohexane and methanol. In cyclohexane, the S 1 state has the nπ* configuration and is short-lived [τ(S 1 ) ∼ 12 ps]. In methanol, a polar and protic solvent, the S 1 state is much shorter-lived [τ (S 1 ) < 1ps, and hence, we have not been able to detect any transient, even in subpicosecond time scale] because of the formation of an intermolecular hydrogen-bonded complex with the solvent. In all other solvents, the S 1 state has a ππ* or CT configuration and, hence, is much longer-lived (>100 ps). The triplet yield is much higher in nonpolar solvents than in polar solvents but the lifetime shows the reverse trend. In nonpolar solvents, the T 1 state is an equilibrium mixture of the states having nπ* and ππ* configurations because of their close proximity in energy, and it is photochemically reactive toward hydrogen-atom-abstraction reactions. In polar solvents, the T 1 state is unreactive because of its ππ* or CT character. A comparison has also been made among the photophysical properties of benzophenone (BP), p-hydroxybenzophenone (p-HOBP), and p-ABP.
“…Photoexcitation of BP to the S 1 state is followed by rapid intersystem crossing (ISC) with unit quantum yield to the triplet state. , Formation of the triplet state absorption (λ max = 530 nm) can be observed spectroscopically. Several transient spectroscopic studies have revealed that the growth of the triplet state takes places in a range of 6 to 30 ps depending on the solvent. , …”
Two modes of excitation (S 0 f S 2 and S 0 f S 1 ) of benzophenone (BP) and p-iodobenzophenone (p-IBP) in acetonitrile have been examined by ultrafast pump-probe experiments. The S 1 states (λ max ∼ 575-580 nm) of BP and p-IBP were observed to be generated with lifetimes of 0.53 and 0.59 ps, respectively, following excitation at 267 nm, and this has been attributed to the S 2 f S 1 internal conversion. The rates of the S 1 f T 1 ISC have been observed to be similar following either 267 or 335 nm excitation for both BP (∼1 × 10 11 s -1 ) and p-IBP (∼2.3 × 10 11 s -1 ).
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