’’Proximity effects’’ in radiationless transitions of aromatic molecules with nonbonding electrons: Substituent and temperature dependences of luminescence in some <i>N</i>-heterocyclics

Madej, Suzanne Lyle; Okajima, S.; Lim, E. C.

doi:10.1063/1.433148

Cited by 52 publications

(18 citation statements)

References 7 publications

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“…The introduction of a proton unto the azomethine bridges enhances the nonradiative de-excitation of the excited singlet state. Again, according to the energy gap (proximity effects) law [30][31][32], radiationless transitions to the ground state are more probable from S 1 states of the protonated species than those of their non-protonated analogs. The values of F T obtained in the presence of oxygen were similar to those in the absence of oxygen.…”

Section: Photophysical and Photochemical Studiesmentioning

confidence: 99%

Protonation of some non-transition metal phthalocyanines — spectral and photophysicochemical consequences

Ogunsipe

Idowu

Ogunbayo

et al. 2012

J. Porphyrins Phthalocyanines

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The photophysics and photochemistry of phthalocyanine complexes of magnesium (MgPc), aluminum chloride (ClAlPc) and zinc (ZnPc) are studied in N, N′-dimethylformamide (DMF). The values obtained for the photophysical and photochemical parameters are normal for simple metallophthalocyanine (MPc) complexes. Protonation of the azomethine bridges reduced the photoactivities of the complexes considerably; however the excited triplet states of the protonated species are more stable towards ground state oxygen. The interaction of the non-protonated MPcs with ground state oxygen is shown to be diffusion-assisted, with bimolecular rate constant values of the order of 10 10 M -1 .s -1 . MgPc could not be protonated; it was easily demetalated by the protonating acid. The kinetics of the demetalation yielded the rate equation: Rate = 0.1[MgPc][H + ] 2/3 .

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Section: Photophysical and Photochemical Studiesmentioning

confidence: 99%

Protonation of some non-transition metal phthalocyanines — spectral and photophysicochemical consequences

Ogunsipe

Idowu

Ogunbayo

et al. 2012

J. Porphyrins Phthalocyanines

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“…38,40 Although state inversion does not occur in isoquinoline, the frequency of the n,π* transition is, nonetheless, decreased in aprotic solvents, and there is a smaller energy gap between the n,π* and π,π* states. 38,40 Although state inversion does not occur in isoquinoline, the frequency of the n,π* transition is, nonetheless, decreased in aprotic solvents, and there is a smaller energy gap between the n,π* and π,π* states.…”

Section: ∆G°(tf)mentioning

confidence: 99%

“…The vibronic coupling occurs through the out-of-plane vibrations of the S 1 state which are good acceptor modes for a large energy gap transition such as S 1 -S 0 internal conversion. 40 Therefore, internal conversion is facilitated in aprotic solvents by the proximity effect, thus inhibiting fluorescence.…”

Section: ∆G°(tf)mentioning

confidence: 99%

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Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

et al. 1997

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The isobaric acid/base equilibrium between acridine and the acridinium cation was measured from ambient temperature to 380°C (above the critical temperature of water, T c ) 374°C) using absorption spectroscopy. At 3500 psia, the isobaric protonation of acridine is shown to be exothermic up to approximately 315°C. Above 315°C, protonation becomes endothermic due to changes in the dielectric constant of water with temperature, which has a profound influence on the solvation of ions. The results are interpreted using a modified Born equation to account for the temperature-dependent changes in acridinium cation and proton solvation. The absorption and fluorescence spectra and the fluorescence lifetime of acridine are sensitive to changes in solvent-solute hydrogen bonding. Hydrogen bonding between acridine and water is observed to decrease from ambient temperature to the critical temperature. A relatively rapid change in hydrogen bonding occurs between 100 and 200°C.Acridine in Subcritical and Supercritical Water

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“…These molecules are often cited as classical examples of the "proximity effect," i.e., acceleration of the radiationless decay of the lowest excited na* (or TT*) state by vibronic interaction with a higher mr* (or nv*) state [26]. Madej et al [28] have shown that the lifetime of the TI (n.rr*) state of pyrazine is shortened markedly by methyl substitution (18.5 ms in P, 6.8 ms in MP, and 0.8 ms in DMP in polycrystalline methylcyclohexane at 77 K) due to increased radiationless decay rates. It was proposed that the closer proximity of the Tl(nn-*) and the T2(mr*) states in MP and DMP relative to the parent molecule results in greater out-of-plane distortion of the potential energy surface in the Tl MP and TI DMP, which, in turn, leads to increased Franck-Condon factors (and, hence, to increased rate constants) for the radiationless decay.…”

Section: A Ti Nonradiative Decay Rates Of Pyrazine and Its Methyl Dementioning

confidence: 99%

Model study of the abrupt excess‐energy dependence of radiationless decay in benzene and azabenzenes

Sobolewski

Lim

Siebrand

1991

Int J of Quantum Chemistry

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Model studies are reported aimed at accounting for the abrupt dependence of radiationless decay-rate constants on excess energy (known as channel-three decay in the case of S1 benzene) in singlet and triplet manifolds of benzene and azabenzenes. The favored model involves L.(TT*) state, strongly distorted along an out-of-plane coordinate, crossing the ground-state potential at an energy close to the minimum of the lowest excited state. The results are compared with experimental observations on benzene and three azabenzenes. Implications for photochemical reactions are also discussed.

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’’Proximity effects’’ in radiationless transitions of aromatic molecules with nonbonding electrons: Substituent and temperature dependences of luminescence in some N-heterocyclics

Cited by 52 publications

References 7 publications

Protonation of some non-transition metal phthalocyanines — spectral and photophysicochemical consequences

Protonation of some non-transition metal phthalocyanines — spectral and photophysicochemical consequences

Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

Model study of the abrupt excess‐energy dependence of radiationless decay in benzene and azabenzenes

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