Abstract

We have developed a method to measure triplet optical densities ODr(λ) when considerable photodecomposition is present. The method is demonstrated on Coumarin 120. By focusing an UV cw laser beam on a sample with the aid of a lens, high triplet optical densities ODT(λ) can be recorded. However, the excitation of organic compounds with light causes varying degrees of photodecomposition. In order to take photodecomposition into account, one records triplet optical-density values as well as the accumulation of absorbing photoproducts as a function of time. Turning off the cw laser excitation, one records the accumulation of photoproducts only. Separating the two processes, one can determine how the triplet optical density ODT declines as a function of time t. The obtained curve can be expressed with an equation that appears to decline exponentially with time. This allows one to extrapolate back to t = 0 and recover ODT when there was no photodecomposition. The extrapolated ODT values are used to obtain triplet-extinction coefficients ∊T(λ) by McClure’s method of Coumarin 120.

© 1992 Optical Society of America

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References

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  1. G. N. Lewis, D. Lipkin, T. T. Magel, “Reversible photochemical processes in rigid media. A study of the phosphorescence state,” J. Am. Chem. Soc. 63, 3005–3018 (1941).
    [CrossRef]
  2. I. Carmichael, G. L. Hug, “Triplet–triplet absorption spectra of organic molecules in condensed phases,” J. Phys. Chem. Ref. Data 15, 1–250 (1986).
    [CrossRef]
  3. T. G. Pavlopoulos, Ber. Bunsenges., “Polarization of the triplet–triplet absorption spectrum of 1,2-benzopyrene,” Phys. Chem. 74, 989–992 (1970).
  4. J. Langelaar, J. Wegdam-Van Beck, J. D. W. Voorst, D. Lavalette, “Polarization measurements on low-lying T–T absorptions with cw argon-ion laser photoselection,” Chem. Phys. Lett. 6, 460–464 (1970).
    [CrossRef]
  5. T. G. Pavlopoulos, “Triplet–triplet absorption and polarization spectra of trans-stilbene and some of its derivatives,” Spectrochim. Acta Part A 41, 1357–1358 (1985).
    [CrossRef]
  6. T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes II,” J. Appl. Phys. 67, 1203–1209 (1990).
    [CrossRef]
  7. T. G. Pavlopoulos, “Measurement of triplet extinction coefficients of organic compounds by McClure’s method,” Spectrochim. Acta. Part A 43, 1201–1208 (1987).
    [CrossRef]
  8. D. McClure, “Excited triplet states of some polyatomic molecules,” J. Chem. Phys. 19, 670–675 (1951).
    [CrossRef]
  9. T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes I,” J. Appl. Phys. 64, 521–527 (1988).
    [CrossRef]
  10. M. Maeda, Laser Dyes (Academic, San Diego, Calif., 1984), Chap. 6, p. 184.
  11. G. Jones, “Photochemistry of laser dyes,” in Dye Laser Principles, F. J. Duarte, L. W. Hillman, eds. (Academic, San Diego, Calif., 1990), pp. 287–343.

1990 (1)

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes II,” J. Appl. Phys. 67, 1203–1209 (1990).
[CrossRef]

1988 (1)

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes I,” J. Appl. Phys. 64, 521–527 (1988).
[CrossRef]

1987 (1)

T. G. Pavlopoulos, “Measurement of triplet extinction coefficients of organic compounds by McClure’s method,” Spectrochim. Acta. Part A 43, 1201–1208 (1987).
[CrossRef]

1986 (1)

I. Carmichael, G. L. Hug, “Triplet–triplet absorption spectra of organic molecules in condensed phases,” J. Phys. Chem. Ref. Data 15, 1–250 (1986).
[CrossRef]

1985 (1)

T. G. Pavlopoulos, “Triplet–triplet absorption and polarization spectra of trans-stilbene and some of its derivatives,” Spectrochim. Acta Part A 41, 1357–1358 (1985).
[CrossRef]

1970 (2)

T. G. Pavlopoulos, Ber. Bunsenges., “Polarization of the triplet–triplet absorption spectrum of 1,2-benzopyrene,” Phys. Chem. 74, 989–992 (1970).

J. Langelaar, J. Wegdam-Van Beck, J. D. W. Voorst, D. Lavalette, “Polarization measurements on low-lying T–T absorptions with cw argon-ion laser photoselection,” Chem. Phys. Lett. 6, 460–464 (1970).
[CrossRef]

1951 (1)

D. McClure, “Excited triplet states of some polyatomic molecules,” J. Chem. Phys. 19, 670–675 (1951).
[CrossRef]

1941 (1)

G. N. Lewis, D. Lipkin, T. T. Magel, “Reversible photochemical processes in rigid media. A study of the phosphorescence state,” J. Am. Chem. Soc. 63, 3005–3018 (1941).
[CrossRef]

Bunsenges., Ber.

T. G. Pavlopoulos, Ber. Bunsenges., “Polarization of the triplet–triplet absorption spectrum of 1,2-benzopyrene,” Phys. Chem. 74, 989–992 (1970).

Carmichael, I.

I. Carmichael, G. L. Hug, “Triplet–triplet absorption spectra of organic molecules in condensed phases,” J. Phys. Chem. Ref. Data 15, 1–250 (1986).
[CrossRef]

Golich, D. J.

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes II,” J. Appl. Phys. 67, 1203–1209 (1990).
[CrossRef]

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes I,” J. Appl. Phys. 64, 521–527 (1988).
[CrossRef]

Hug, G. L.

I. Carmichael, G. L. Hug, “Triplet–triplet absorption spectra of organic molecules in condensed phases,” J. Phys. Chem. Ref. Data 15, 1–250 (1986).
[CrossRef]

Jones, G.

G. Jones, “Photochemistry of laser dyes,” in Dye Laser Principles, F. J. Duarte, L. W. Hillman, eds. (Academic, San Diego, Calif., 1990), pp. 287–343.

Langelaar, J.

J. Langelaar, J. Wegdam-Van Beck, J. D. W. Voorst, D. Lavalette, “Polarization measurements on low-lying T–T absorptions with cw argon-ion laser photoselection,” Chem. Phys. Lett. 6, 460–464 (1970).
[CrossRef]

Lavalette, D.

J. Langelaar, J. Wegdam-Van Beck, J. D. W. Voorst, D. Lavalette, “Polarization measurements on low-lying T–T absorptions with cw argon-ion laser photoselection,” Chem. Phys. Lett. 6, 460–464 (1970).
[CrossRef]

Lewis, G. N.

G. N. Lewis, D. Lipkin, T. T. Magel, “Reversible photochemical processes in rigid media. A study of the phosphorescence state,” J. Am. Chem. Soc. 63, 3005–3018 (1941).
[CrossRef]

Lipkin, D.

G. N. Lewis, D. Lipkin, T. T. Magel, “Reversible photochemical processes in rigid media. A study of the phosphorescence state,” J. Am. Chem. Soc. 63, 3005–3018 (1941).
[CrossRef]

Maeda, M.

M. Maeda, Laser Dyes (Academic, San Diego, Calif., 1984), Chap. 6, p. 184.

Magel, T. T.

G. N. Lewis, D. Lipkin, T. T. Magel, “Reversible photochemical processes in rigid media. A study of the phosphorescence state,” J. Am. Chem. Soc. 63, 3005–3018 (1941).
[CrossRef]

McClure, D.

D. McClure, “Excited triplet states of some polyatomic molecules,” J. Chem. Phys. 19, 670–675 (1951).
[CrossRef]

Pavlopoulos, T. G.

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes II,” J. Appl. Phys. 67, 1203–1209 (1990).
[CrossRef]

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes I,” J. Appl. Phys. 64, 521–527 (1988).
[CrossRef]

T. G. Pavlopoulos, “Measurement of triplet extinction coefficients of organic compounds by McClure’s method,” Spectrochim. Acta. Part A 43, 1201–1208 (1987).
[CrossRef]

T. G. Pavlopoulos, “Triplet–triplet absorption and polarization spectra of trans-stilbene and some of its derivatives,” Spectrochim. Acta Part A 41, 1357–1358 (1985).
[CrossRef]

T. G. Pavlopoulos, Ber. Bunsenges., “Polarization of the triplet–triplet absorption spectrum of 1,2-benzopyrene,” Phys. Chem. 74, 989–992 (1970).

Voorst, J. D. W.

J. Langelaar, J. Wegdam-Van Beck, J. D. W. Voorst, D. Lavalette, “Polarization measurements on low-lying T–T absorptions with cw argon-ion laser photoselection,” Chem. Phys. Lett. 6, 460–464 (1970).
[CrossRef]

Wegdam-Van Beck, J.

J. Langelaar, J. Wegdam-Van Beck, J. D. W. Voorst, D. Lavalette, “Polarization measurements on low-lying T–T absorptions with cw argon-ion laser photoselection,” Chem. Phys. Lett. 6, 460–464 (1970).
[CrossRef]

Chem. Phys. Lett. (1)

J. Langelaar, J. Wegdam-Van Beck, J. D. W. Voorst, D. Lavalette, “Polarization measurements on low-lying T–T absorptions with cw argon-ion laser photoselection,” Chem. Phys. Lett. 6, 460–464 (1970).
[CrossRef]

J. Am. Chem. Soc. (1)

G. N. Lewis, D. Lipkin, T. T. Magel, “Reversible photochemical processes in rigid media. A study of the phosphorescence state,” J. Am. Chem. Soc. 63, 3005–3018 (1941).
[CrossRef]

J. Appl. Phys. (2)

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes II,” J. Appl. Phys. 67, 1203–1209 (1990).
[CrossRef]

T. G. Pavlopoulos, D. J. Golich, “Triplet extinction coefficients of some laser dyes I,” J. Appl. Phys. 64, 521–527 (1988).
[CrossRef]

J. Chem. Phys. (1)

D. McClure, “Excited triplet states of some polyatomic molecules,” J. Chem. Phys. 19, 670–675 (1951).
[CrossRef]

J. Phys. Chem. Ref. Data (1)

I. Carmichael, G. L. Hug, “Triplet–triplet absorption spectra of organic molecules in condensed phases,” J. Phys. Chem. Ref. Data 15, 1–250 (1986).
[CrossRef]

Phys. Chem. (1)

T. G. Pavlopoulos, Ber. Bunsenges., “Polarization of the triplet–triplet absorption spectrum of 1,2-benzopyrene,” Phys. Chem. 74, 989–992 (1970).

Spectrochim. Acta Part A (1)

T. G. Pavlopoulos, “Triplet–triplet absorption and polarization spectra of trans-stilbene and some of its derivatives,” Spectrochim. Acta Part A 41, 1357–1358 (1985).
[CrossRef]

Spectrochim. Acta. Part A (1)

T. G. Pavlopoulos, “Measurement of triplet extinction coefficients of organic compounds by McClure’s method,” Spectrochim. Acta. Part A 43, 1201–1208 (1987).
[CrossRef]

Other (2)

M. Maeda, Laser Dyes (Academic, San Diego, Calif., 1984), Chap. 6, p. 184.

G. Jones, “Photochemistry of laser dyes,” in Dye Laser Principles, F. J. Duarte, L. W. Hillman, eds. (Academic, San Diego, Calif., 1990), pp. 287–343.

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Figures (3)

Fig. 1
Fig. 1

Three typical monitoring light intensity traces as functions of time t and wavelengths λ (A = 580 nm, B = 480 nm, and C = 440 nm), recorded with the aid of a strip-chart recorder. Starting with Io = 100 (relative light intensity), the sample containing a 1 × 10−4 M solution of Coumarin 120 dissolved in a mixture of n-butanol/isopentane with a ratio of 3:7 is excited with cw laser light after t = 10 s. After 50 s, the excitation light is turned off. The excited-state molecules NT then decay exponentionally back to the ground (singlet) state NS, and one measures Io′.

Fig. 2
Fig. 2

Plots of 1/ODT(t = 0) versus 1/Iex, to obtain 1 / O D T by extrapolation for the concentrations 1 and 2 × 10−4 M. The ODT(t = 0) ≡ A values were calculated with the aid of Eq. (10). Measurements were performed at 580 nm, which is near the T–T absorption maximum.

Fig. 3
Fig. 3

T–T absorption spectrum presented as ∊T and absorption spectrum of the photodecomposition products presented as ODP as a function of wavelength λ of the Coumarin 120.

Tables (1)

Tables Icon

Table I Extrapolated Triplet Optical Densities ODT(t = 0) According to Eq. (10) as a Function of Wavelengths λ

Equations (11)

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O D T ( λ ) log I o / I T = N T T ( λ ) d .
N S + h υ A N S + N T .
N S + h υ A N S + N T + N P .
O D T ( t n , λ ) log I o ( t n , λ ) / I ( t n , λ ) = N T ( t n ) T ( λ ) d .
I I T + P = I o × 10 10 N T T d N P P d ,
I o I P = I o × 10 N P P d ,
I T = I o × 10 N T T d ,
I I T + P = I P 10 N T T d = I o × 10 N T T d ,
O D T ( λ ) log I P / I T + P = log I o / I = N T T d ,
O D T ( t ) = A exp ( k t ) ,
1 / O D T = ( 1 / N T T d ) ( 1 + A i / I ex ) ,

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