The deactivation of singlet excited all-trans-1,6-diphenylhexa-1,3,5-triene by charge transfer processes 2. Formation and dynamics of charge transfer (CT) intermediates

Schael, Frank; Küster, Jörn; Löhmannsröben, Hans‐Gerd

doi:10.1016/s0301-0104(97)00051-7

Cited by 6 publications

(4 citation statements)

References 52 publications

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“…The ∆E 1/2 (2.65 V) of the 10MP radical cation-DPH radical anion system in 50/50 ACN/BZ is energy insufficient to populate the singlet state of either 10MP or DPH (∆E 0,0 ) 3.11 eV). 19 Generation of the DPH radical cation was avoided since it fouled the electrode surface resulting in diminishing ECL with time. The spectrum of the emission from the 10MP radical cation-DPH radical anion system generated with a 125 Hz continuous square wave was a broad, featureless wave, of low intensity and with the same λ max as that found with the 10MP-BZO system, Figure 2.…”

Section: Resultsmentioning

confidence: 99%

“…DPH has been investigated photochemically for its fluorescence and for its participation in exciplexes. − On the time scale of electrochemical experiments (ms), DPH forms an unstable radical cation ( E 1/2 = 0.97 vs Ag/AgCl) and a stable radical anion (−2.08 V vs Ag/AgCl). The Δ E 1/2 (2.65 V) of the 10MP radical cation−DPH radical anion system in 50/50 ACN/BZ is energy insufficient to populate the singlet state of either 10MP or DPH (Δ E 0,0 = 3.11 eV) …”

Section: Resultsmentioning

confidence: 99%

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Selective Population of Excited States during Electrogenerated Chemiluminescence with 10-Methylphenothiazine

et al. 2002

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Electrogenerated chemiluminescence of 10-methylphenothiazine (10MP) is demonstrated using the radical cation of 10MP and a variety of radical anions which provided a range of energies from insufficient to form the triplet state of 10MP through sufficient to form the first excited singlet state. When naphthalene was used as the radical anion, the reaction was sufficiently energetic to populate the singlet state of 10MP and the expected spectrum was obtained. When benzophenone was used as the radical anion, the sufficiency of the reaction energy depended upon the dielectric constant of the solvent. At high values ( ) 20) the reaction was energy insufficient and no emission was observed, but at low values ( ) 7) the reaction was sufficiently energetic to populate the triplet and emission was observed at wavelengths significantly longer than that of the excited singlet. Identical emission from 10MP was formed with the radical anion of 1,6-diphenyl-1,3,5hexatriene. The emission results were inconsistent with an exciplex but the available energetics from the radical ion reactions and the susceptibility to quenching suggest an excited triplet state of 10MP. Efforts to corroborate this state photochemically were inconclusive since phosphorescence could only be obtained at 77 K and the spectrum was not identical to the room-temperature electrogenerated chemiluminescence. When three different anthracene derivatives were employed (9,10-diphenylanthracene, 9-phenylanthracene, and 9,-10-dimethylanthracene) as the radical anion, the triplet-like emission was observed from 10MP and also singlet emission from the anthracenes, resulting in a bright, white or pale blue light. This mixed emission has been observed in solid-state systems, but never before in solution ECL.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Selective Population of Excited States during Electrogenerated Chemiluminescence with 10-Methylphenothiazine

et al. 2002

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“…The radical ion pair mechanism was further tested by repeating the measurements in MCH in the presence of fumaronitrile (FN), [DPH] = 2.2 × 10 -3 M, [FN] = 5.4 × 10 -3 M. FN is an excellent electron acceptor that is known to quench 1 DPH* at nearly diffusion-controlled rates in both polar and nonpolar solvents. − If the electron ejection step in eq 3 were playing a role in the development of the 497 nm emission, then competitive capture of ejected electrons by FN would diminish the intensity of this emission. No such quenching was observed.…”

Section: Resultsmentioning

confidence: 99%

Distortion of the Fluorescence Spectrum of all-trans-1,6-Diphenyl-1,3,5-hexatriene with Increasing Laser Pulse Excitation Energies

1999

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At high laser pulse excitation energies the fluorescence spectrum of all-trans-1,6-diphenyl-1,3,5-hexatriene, DPH, undergoes distortion that can be modeled as the development of a new broad fluorescence, λ max ) 497 nm, which builds up biphotonically with increasing excitation laser pulse power. This phenomenon is observed upon excitation at either 266 or 355 nm in a variety of organic solvents, provided [DPH] and excitation intensity are sufficiently high. Four possible sources for the distortion of the fluorescence spectrum are investigated: (1) excimer emission arising from DPH radical cation/anion pairs, (2) bicimer fluorescence from the encounter of two S 1 states, (3) S n f S 1 fluorescence, and (4) self-absorption due to overlap of the fluorescence with transient absorption spectra. The first three possibilities are ruled out. The fourth is viable, revealing an effective transient absorption spectrum that agrees well with the known S n r S 1 absorption spectrum at long wavelengths.

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“…The possible role of DPH radical cations, 2DPH •+ , in the photoisomerization was investigated by using FN to induce their formation. This part of the work was prompted by the elegant studies of charge-transfer quenching of 1 ttt -DPH* by Löhmannsröben and Schael. ,,, Interactions between 1 ttt -DPH* and several electron acceptors, including FN, were investigated in a series of solvents of varying polarity (toluene to AN) using fluorescence and transient absorption measurements. , Exciplexes formed in nonpolar solvents have charge-transfer character and in polar solvents, such as AN, dissociate into free radical ion pairs. Intersystem crossing in the contact radical ion pair followed by back electron transfer leads to 3 DPH* as an important decay channel especially in nonpolar solvents .…”

Section: Discussionmentioning

confidence: 99%

Direct Photoisomerization of the 1,6-Diphenyl-1,3,5-hexatrienes. Medium Effect on Triplet and Singlet Contributions

et al. 2000

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Quantum yields for the interconversion of the all- cis,trans,cis,3, in methylcyclohexane (MCH) or acetonitrile (AN) following 366 nm excitation show these processes to be relatively inefficient. Their dependence on the concentration of the DPH reveals significant participation of triplet states in the overall process. Despite very low intersystem crossing quantum yields (0.029 and 0.010 in MCH and AN, respectively) singlet and triplet contributions in the photoisomerization of all-trans-1,6-diphenyl-1,3,5-hexatriene are roughly equal in MCH, and, for the trans,cis,trans isomer, in AN. However, in AN the cis,trans,trans isomer forms nearly exclusively by a singlet pathway from the other two isomers. The cis,cis,trans isomer, a very minor component in photostationary states, appears to form primarily from the cis,trans,trans isomer whose excited singlet state also gives another isomer, tentatively identified as ctc-DPH. The major radiationless channel of the excited singlet state of each DPH isomer is direct decay to the original ground state. Barriers to torsional relaxation of the planar lowest DPH excited singlet states (2 1 A g and 1 1 B u ) must be significantly higher than previously supposed. Photoisomerization quantum yields of all-trans-DPH in the presence of fumaronitrile (FN) are also separated into singlet and triplet contributions. Fumaronitrile quenches DPH fluorescence and singlet contributions to the photoisomerization equally, but enhances DPH triplet formation and the triplet contribution to the photoisomerization. Radical cations of DPH form in AN but do not participate in isomer interconversion.

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The deactivation of singlet excited all-trans-1,6-diphenylhexa-1,3,5-triene by charge transfer processes 2. Formation and dynamics of charge transfer (CT) intermediates

Cited by 6 publications

References 52 publications

Selective Population of Excited States during Electrogenerated Chemiluminescence with 10-Methylphenothiazine

Selective Population of Excited States during Electrogenerated Chemiluminescence with 10-Methylphenothiazine

Distortion of the Fluorescence Spectrum of all-trans-1,6-Diphenyl-1,3,5-hexatriene with Increasing Laser Pulse Excitation Energies

Direct Photoisomerization of the 1,6-Diphenyl-1,3,5-hexatrienes. Medium Effect on Triplet and Singlet Contributions

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