Kinetic analysis of flash photolysis data for sequential first and second order reactions: The photoreduction of triplet fluorenone by dabco

C60 as a Photocatalyst of Electron-Transfer Processes: Reactions of Triplet C60 with Chloranil, Perylene, and Tritolylamine Studied by Flash Photolysis and FT-EPR

“…The transient spectrum given in Figure shows peaks at 1080, 555, and 485 nm which are unambiguously assigned respectively to the ion radicals, C 60 - and Pe + , and to the triplet, 3 Pe. , Thus, both electron- and energy-transfer reactions contribute to the quenching process: Reaction 1 can be followed most clearly at the absorption peak of C 60 - . Assuming pseudo-first-order radical formation and second-order radical decay ( k d ), we fit the 1080 nm transient profile with k q (= k 1 + k 2 ) = (1.1 ± 0.3) × 10 9 M -1 s -1 , in fair agreement with the measurement at 750 nm, and k d /ε(C 60 - ) 1080 = (4.2 ± 0.5) × 10 5 cm s -1 . With ε(C 60 - ) = 18 300 ± 1100 M -1 cm -1 , determined above, we obtain k d = (7.7 ± 1.2) × 10 9 M -1 s -1 for the bulk radical recombination rate, very close to the diffusion-controlled value and comparable to that found 2 for reaction of C 60 - with TTA + .

3 Time-resolved absorption spectra from a solution of C 60 (∼5 × 10 -5 M) and perylene (5 × 10 -4 M) in benzonitrile immediately (·) and 3 μs (▴) after flash.

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“…The C 60 - extinction coefficient was obtained also from kinetic data. Assuming a second-order back-reaction with rate constant k 2 for radical decay, the slope, S λ , of a plot of Δ D λ -1 vs time following triplet disappearance is k 2 /∑Δε λ , where ∑Δε λ is the total differential extinction coefficient at wavelength λ. Thus, in the C 60 /TTA system, Measured Δ D -1 vs time slopes of TTA + and C 60 - peaks are plotted in Figure .…”

“…Quantum Yields . Nonlinear least-squares analysis of the transient profiles gives also the values of product absorbances corrected for decay during the formation period and corresponding to total product yields . Quantum yields referred to the triplet are then given by where is the initial absorbance of 3 C 60 .…”

“…Flash photolysis studies utilized a flash lamp driven dye laser (Candela ED-200) giving 0.2 µs pulses at 590 nm (rhodamine 6G). Initial triplet absorbance on flashing [C 60 ] ∼ 7 × 10 -5 M in benzonitrile (∆D 750 ∼ 0.6) corresponded to [ 3 C 60 ] 0 ∼ 4 × 10 -5 M. Transient absorption spectra were followed by conventional means, 13 using a photomultiplier to 800 nm and an InGaAs photodiode and fast amplifier (New Focus, 1811) for the near-IR. Quenching rate constants were determined from the linear dependence of pseudo-first-order decay constants on quencher concentration.…”

Μελέτη Της Φωτοχημείας Και Της Φωτοεκκινητικής Ικανότητας Διχρωμοφορικών Αρωματικών Κετονών Σε Σύστημα Φωτοπολυμερισμού ΜΜΑ Τύπου ΙΙ

“…[179] ߔ αντιδραστηρίου. [182][183][184][185][186][187][188][189][190][191][192][193] Η δραστικότητα των αρωματικών κετονών κατά την απόσπαση πρωτονίου, εξαρτάται έντονα από το χαρακτήρα της χαμηλότερης τριπλής της κατάστασης. Η διαμόρφωση που επικρατεί σε κάθε κετόνη ( 3 ππ* ή 3 nπ*) εξαρτάται με τη σειρά της από τη φύση και τη θέση των υποκαταστατών στο χρωμοφόρο, καθώς και από τις ιδιότητες του διαλύτη.…”