Abstract

Triplet-triplet (T-T) absorption spectra of organic compounds (e.g., dyes) are conveniently obtained by the steady-state method employing an ultraviolet/blue cw laser as an excitation source. The large depletion of molecules in the ground singlet state allows accurate determination of molar triplet extinction coefficients ε<sub><i>T</i></sub> without the knowledge of additional kinetic parameters. An approximation method is presented, which allows reasonably accurate determination of the concentration of triplet molecules [and consequently ε<sub><i>T</i></sub>(λ)] at the onset of the singlet-singlet (S-S) absorption. This method is of interest in cases in which strong S-S and strong T-T absorption overlap. The ε<sub><i>T</i></sub> of brilliant sulphaflavine in the region from 4700 to 6520 Å was measured. As the excitation source, the 4416-Å line of a 50-mW He-Cd cw laser was used. A 45% depletion of the singlet-ground-state population was observed.

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  1. G. Porter and M. W. Windsor, Proc. R. Soc. Lond. 245, 238 (1958). This paper also contains older references on the subject.
  2. D. Lavalette, J. Chim. Phys. 66, 1853 (1969). Reference article on methods of measuring triplet extinction coefficients.
  3. T. G. Pavlopoulos, Ber. Bunsenges. Phys. Chem. 74, 989 (1970).
  4. J. Langelaar, J. Wegdam-Van Beek, J. D. W. Van Voorst, and D. Lavalette, Chem. Phys. Lett. 6, 460 (1970).
  5. This can be accomplished by closing the optical liquid-nitrogen dewar with a rubber cork with two holes in it. Through one of the holes, a plastic tube from the storage contained transfers liquid nitrogen directly into the optical dewar. The second hole allows gaseous nitrogen to escape, at sufficient pressure to keep air out. When measurements are being made, or the optical dewar is being transported the dewar is closed with a rubber cork fitted with a pressure relief valve. The valve consists of a glass or metal tube through the rubber cork and about 7 cm of rubber tubing on the end of the glass or metal tube. The end of the rubber tubing is sealed; a diagonal cut half-way through the rubber tubing, made with a razor blade, permits nitrogen to escape and prevents air from entering.
  6. A Brower Laboratories model No. 131 lock-in voltmeter, which operates with fixed chopping frequencies, and a Keithley System No. 82 lock-in amplifier also performed satisfactorily.
  7. B. B. Snavely, Proc. Inst. Electr. Eng. 57, 1374 (1969).
  8. J. B. Marlin, D. W. Gregg, and I. Wood, Appl. Phys. Lett. 17, 527 (1970).
  9. D. S. McClure, J. Chem. Phys. 19, 670 (1951).
  10. D. P. Craig and I. G. Ross, J. Chem. Soc. (Lond.) 1954, 1589 (1954).
  11. Large depletion effects were observed by exciting 4,8-dimethyl-7-hydroxycoumarin and 4-methyl-7-hydroxycoumarin with the 3250-Å line of the 15-mW He-Cd cw laser. The experiments were discontinued when these molecules showed large photodecomposition. The experimental setup used for the determination of εT can also be used to obtain data on photodecomposition rates. Both decay of the T-T absorption and decay of S-S depletion densities as functions of time can be used for this type of kinetic experiment.

Beek, J. Wegdam-Van

J. Langelaar, J. Wegdam-Van Beek, J. D. W. Van Voorst, and D. Lavalette, Chem. Phys. Lett. 6, 460 (1970).

Craig, D. P.

D. P. Craig and I. G. Ross, J. Chem. Soc. (Lond.) 1954, 1589 (1954).

Gregg, D. W.

J. B. Marlin, D. W. Gregg, and I. Wood, Appl. Phys. Lett. 17, 527 (1970).

Langelaar, J.

J. Langelaar, J. Wegdam-Van Beek, J. D. W. Van Voorst, and D. Lavalette, Chem. Phys. Lett. 6, 460 (1970).

Lavalette, D.

J. Langelaar, J. Wegdam-Van Beek, J. D. W. Van Voorst, and D. Lavalette, Chem. Phys. Lett. 6, 460 (1970).

D. Lavalette, J. Chim. Phys. 66, 1853 (1969). Reference article on methods of measuring triplet extinction coefficients.

Marlin, J. B.

J. B. Marlin, D. W. Gregg, and I. Wood, Appl. Phys. Lett. 17, 527 (1970).

McClure, D. S.

D. S. McClure, J. Chem. Phys. 19, 670 (1951).

Pavlopoulos, T. G.

T. G. Pavlopoulos, Ber. Bunsenges. Phys. Chem. 74, 989 (1970).

Porter, G.

G. Porter and M. W. Windsor, Proc. R. Soc. Lond. 245, 238 (1958). This paper also contains older references on the subject.

Ross, I. G.

D. P. Craig and I. G. Ross, J. Chem. Soc. (Lond.) 1954, 1589 (1954).

Snavely, B. B.

B. B. Snavely, Proc. Inst. Electr. Eng. 57, 1374 (1969).

Van Voorst, J. D. W.

J. Langelaar, J. Wegdam-Van Beek, J. D. W. Van Voorst, and D. Lavalette, Chem. Phys. Lett. 6, 460 (1970).

Windsor, M. W.

G. Porter and M. W. Windsor, Proc. R. Soc. Lond. 245, 238 (1958). This paper also contains older references on the subject.

Wood, I.

J. B. Marlin, D. W. Gregg, and I. Wood, Appl. Phys. Lett. 17, 527 (1970).

Other

G. Porter and M. W. Windsor, Proc. R. Soc. Lond. 245, 238 (1958). This paper also contains older references on the subject.

D. Lavalette, J. Chim. Phys. 66, 1853 (1969). Reference article on methods of measuring triplet extinction coefficients.

T. G. Pavlopoulos, Ber. Bunsenges. Phys. Chem. 74, 989 (1970).

J. Langelaar, J. Wegdam-Van Beek, J. D. W. Van Voorst, and D. Lavalette, Chem. Phys. Lett. 6, 460 (1970).

This can be accomplished by closing the optical liquid-nitrogen dewar with a rubber cork with two holes in it. Through one of the holes, a plastic tube from the storage contained transfers liquid nitrogen directly into the optical dewar. The second hole allows gaseous nitrogen to escape, at sufficient pressure to keep air out. When measurements are being made, or the optical dewar is being transported the dewar is closed with a rubber cork fitted with a pressure relief valve. The valve consists of a glass or metal tube through the rubber cork and about 7 cm of rubber tubing on the end of the glass or metal tube. The end of the rubber tubing is sealed; a diagonal cut half-way through the rubber tubing, made with a razor blade, permits nitrogen to escape and prevents air from entering.

A Brower Laboratories model No. 131 lock-in voltmeter, which operates with fixed chopping frequencies, and a Keithley System No. 82 lock-in amplifier also performed satisfactorily.

B. B. Snavely, Proc. Inst. Electr. Eng. 57, 1374 (1969).

J. B. Marlin, D. W. Gregg, and I. Wood, Appl. Phys. Lett. 17, 527 (1970).

D. S. McClure, J. Chem. Phys. 19, 670 (1951).

D. P. Craig and I. G. Ross, J. Chem. Soc. (Lond.) 1954, 1589 (1954).

Large depletion effects were observed by exciting 4,8-dimethyl-7-hydroxycoumarin and 4-methyl-7-hydroxycoumarin with the 3250-Å line of the 15-mW He-Cd cw laser. The experiments were discontinued when these molecules showed large photodecomposition. The experimental setup used for the determination of εT can also be used to obtain data on photodecomposition rates. Both decay of the T-T absorption and decay of S-S depletion densities as functions of time can be used for this type of kinetic experiment.

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