Excited singlet (S1) state interactions of 2,2′- and 4,4′-biphenyldiols with chloroalkanes: Photoinduced dissociative electron transfer

Mohanty, Jyotirmayee; Pal, Haridas; Sapre, A. V.

doi:10.1063/1.1464824

Cited by 14 publications

(6 citation statements)

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“…The Φ f values were measured in a comparative method, , using Φ f = 0.19 for C151 dye in hexane as the reference. , Fluorescence lifetimes were measured using a time-correlated single-photon-counting (TCSPC) spectrometer, , model 199, form Edinburgh Instrument, U.K. The details of this instrument have been given elsewhere. , Briefly, a thyratron-triggered hydrogen discharge lamp (30 kHz) having a pulse width of ∼1.2 ns (at fwhm) was used as the excitation source. Observed fluorescence decays were analyzed following reconvolution procedure, , using a proper instrument response function.…”

Section: Methodsmentioning

confidence: 99%

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Photophysical Properties of Coumarin-152 and Coumarin-481 Dyes: Unusual Behavior in Nonpolar and in Higher Polarity Solvents

2003

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Solvent polarity and temperature effect on the photophysical properties of two 1,2-benzopyrone dyes, namely, coumarin-152 (C152) and coumarin-481 (C481), have been investigated using steady-state and time-resolved fluorescence measurements. In nonpolar (NP) solvents (e.g., hexane, cyclohexane, methylcyclohexane, 2-methylpentane, and 3-methylpentane), the Stokes' shifts (Δν̄) and fluorescence lifetimes (τf) for both the dyes are unexpectedly lower. Excluding NP solvents, for all other solvents the Δν̄ correlates linearly with the solvent polarity function, Δf = {(ε − 1)/(2ε + 1) − (n 2 − 1)/(2n 2 + 1)}, and the slopes of these plots indicate that the fluorescent states for both the dyes in these solvents are of intramolecular charge transfer (ICT) character. The unusually lower Δν̄ and τf values in NP solvents have been rationalized considering nonpolar structures for the fluorescent states of the dyes in these solvents. The fluorescence quantum yields (Φf) and τf values of the two dyes also show an unusual reduction in higher polarity solvents (Δf > ∼0.2). Furthermore, unlike in all other solvents, in solvents with Δf > ∼0.2, the Φf and τf values are strongly temperature-dependent. These results indicated the involvement of a new activation-controlled nonradiative deexcitation channel in higher polarity solvents, assigned to the involvement of the nonfluorescent twisted intramolecular charge transfer (TICT) state. Though the activation barrier (ΔE a) for such processes usually decreases with solvent polarity, for the present systems the ΔE a is seen to increase with Δf. This unusual behavior has been rationalized assuming that the ΔE a arises because of the potential energy (PE) crossing of the TICT and ground states rather than that of the ICT and TICT states as is usually the case for most TICT molecules. On increasing Δf, since the highly polar TICT state not only gets better stabilization but also its PE surface becomes more steeper than the ICT state, the ΔE a effectively increases with solvent polarity.

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Section: Methodsmentioning

confidence: 99%

“…The details of this instrument have been given elsewhere. 46,47 Briefly, a thyratron-triggered hydrogen discharge lamp (30 kHz) having a pulse width of ∼1.2 ns (at fwhm) was used as the excitation source. Observed fluorescence decays were analyzed following reconvolution procedure, 44,45 using a proper instrument response function.…”

Section: Introductionmentioning

confidence: 99%

Photophysical Properties of Coumarin-152 and Coumarin-481 Dyes: Unusual Behavior in Nonpolar and in Higher Polarity Solvents

2003

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“…In the case of quenching of NAP(T n ), DBA(T n ), and CHR(T n ) by RCl such as CCl 4 , CH 2 Cl 2 , and 1,2-dichloroethane in acetonitrile, l s ¼ 128 kJ mol À1 (1.33 eV) can be used similar to the reports in which RCl quenching 2,2 0 -and 4,4 0 -biphenyldiols in the S 1 states were studied. 36,37 Usually, l v value is quite small or negligible. 1,2 According to eqn.…”

Section: No Occurrence Of Elt Quenching Of Ah(t N ) By Qmentioning

confidence: 99%

“…l v became unusually high compare to the normal organic donor-acceptor systems. 36,37 l ¼ 352 kJ mol À1 (3.65 eV) was selected. Similarly, the simultaneous C-Cl bond cleavage of RCl accompanied TENT or ELT from AH(T n ) should also be considered in our system.…”

Section: No Occurrence Of Elt Quenching Of Ah(t N ) By Qmentioning

confidence: 99%

Quenching processes of aromatic hydrocarbons in the higher triplet excited states-energy transfer vs. electron transferElectronic supplementary information (ESI) available: The quenching of DBA(Tn) by CCl4, CHR(Tn) by NAP, the evidences of no DBA and CHR ions produced during two-color two-laser flash photolysis, and the evidence of formation of benzene/Cl complex. See http://www.rsc.org/suppdata/cp/b4/b400128a/

Cai

Sakamoto

Hara

et al. 2004

Phys. Chem. Chem. Phys.

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“…The D R values of the C−Cl bond are 3.17 eV for CCl 4 , 3.25 eV for CH 2 Cl 2 , and 3.52 eV for DCE . Such large D R values cause the substantial decrease in the ELT rate ( k ELT < 10 8 M -1 s -1 ). ,, The ELT from PP(T n ) to RCl may occur competitively with other rapid processes, such as internal conversion and TENT with the rate constant of k TENT = k diff , when the free energy change (−Δ G TENT ) is larger than 13 kJ mol -1 . , From the E T 1 values of PP(T 1 ) in Table and the transient absorption edge of PP(T 1 ), the T n state energies of PP(T n ) ( E PP(T n ) ) were calculated to be 555, 483, and 486 kJ mol -1 for BP(T n ), TP(T n ), and TPB(T n ) (these calculated E PP(Tn) values correspond to PP(T m ) ( E PP(T m ) ) in Scheme , see the below discussion), respectively, which are much larger than the D R values of the C−Cl bond of RCl. Consequently, the occurrence of the TENT from PP(T n ) to RCl at k diff is much faster than the ELT from PP(T n ) to RCl …”

Section: Resultsmentioning

confidence: 99%

Transient Phenomena of Polyphenyls in the Higher Triplet Excited State

et al. 2004

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Transient phenomena of polyphenyls (PP), such as biphenyl (BP), p-terphenyl (TP), and 1,3,5-triphenylbenzene (TPB) in the higher triplet excited states (T n , n g 2), were investigated with the nanosecond-nanosecond (ns-ns) two-color two-laser excitation method. PP(T n ) was generated by the excitation of PP in the lowest triplet excited state (PP(T 1 )) at the wavelength tuned to the absorption of PP(T 1 ). Bleaching of the transient absorption of BP(T 1 ) and TP(T 1 ) was observed during the second laser irradiation in the presence of chloroalkanes (RCl) such as carbon tetrachloride (CCl 4 ), dichloromethane (CH 2 Cl 2 ), or 1,2-dichloroethane (DCE). In the case of TPB, clear bleaching of TPB(T 1 ) was observed in the presence of CCl 4 , while no bleaching was observed in the presence of CH 2 Cl 2 and DCE. No formation of PP •+ was detected during the quenching of PP(T n ) by RCl. Therefore, the bleaching of PP(T 1 ) is attributed to triplet energy transfer quenching of PP(T n ) by RCl followed by the C-Cl bond cleavage. The lifetimes (τ Tn ) of PP(T n ) were estimated from the dependence of the quenching efficiency on the RCl concentration. It was found that the τ Tn value decreased with the increasing number of benzene rings, BP(T n ) (950 ps) > TP(T n ) (620 ps) > TPB(T n ) (360 ps). The quenching mechanism of PP(T n ) by RCl was discussed.

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Excited singlet (S1) state interactions of 2,2′- and 4,4′-biphenyldiols with chloroalkanes: Photoinduced dissociative electron transfer

Abstract: Excited singlet (S 1 ) state interactions of calixarenes with chloroalkanes: A combination of concerted and stepwise dissociative electron transfer mechanism

Cited by 14 publications

References 50 publications

Photophysical Properties of Coumarin-152 and Coumarin-481 Dyes: Unusual Behavior in Nonpolar and in Higher Polarity Solvents

Photophysical Properties of Coumarin-152 and Coumarin-481 Dyes: Unusual Behavior in Nonpolar and in Higher Polarity Solvents

Transient Phenomena of Polyphenyls in the Higher Triplet Excited State

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