Advertisement

The Triplet State

  • Dwaine O. Cowan
  • Ronald L. Drisko

Abstract

In our discussion in Chapter 1 of the various photophysical processes which can occur in an organic molecule upon absorption of light, we saw that two types of electronic excited states are possible. The first, initially reached upon excitation, is the singlet, in which the electronic spins remain paired. The second, obtained from the excited singlet through a process known as intersystem crossing, is the triplet state, in which the electron spins are antiparallel or unpaired. We have seen in subsequent chapters that a considerable amount of photochemistry is found to arise from the triplet state and in some cases it was suggested that the apparent greater reactivity of the excited triplet as compared to the excited singlet state arises from the greater lifetime of the former. However, we have not considered the questions: What exactly is a triplet state? Why should it be a longer lived state than the singlet? How are its properties different from the singlet? How are these properties determined? In this chapter we will attempt to answer these and other questions concerning the nature of the triplet state.

Keywords

Triplet State Heavy Atom Excited Singlet Triplet Energy Delayed Fluorescence 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    J. Dewar, Proc. Roy. Soc. (London) 36, 164 (1880); Proc. Roy. Inst. G. B. 12, 557 (1888); Proc. Roy. Soc. (London) 43, 1078 (1888).Google Scholar
  2. 2.
    E. Wiedemann, Ann. Phys. 34, 446 (1888).Google Scholar
  3. 3.
    H. Kautsky and A. Hirsch, Ber. 64, 2677 (1931); 65, 401 (1932)Google Scholar
  4. H. Kautsky, A. Hirsch, and F. Davidshofer, Ber. 65, 1762 (1932)Google Scholar
  5. H. Kautsky, H. deBruijn, R. Neuwirth, and W. Baumeister, Ber. 66, 1588 (1933).Google Scholar
  6. 4. (a)
    A. Jablonski, Nature 131, 839 (1933)Google Scholar
  7. (b).
    A. Jablonski Z. Physik. 94, 38 (1935).Google Scholar
  8. 5.
    A. Terenin, Acta Physicochim. URSS 18, 210 (1943); Zh. Fiz. Khim. 18, 1 (1944).Google Scholar
  9. 6.
    G. N. Lewis, D. Lipkin, and T. T. Magel, J. Amer. Chem. Soc. 63, 3005 (1941).Google Scholar
  10. 7.
    G. N. Lewis and M. Kasha, J. Amer. Chem. Soc. 66, 2100 (1944); 67, 994 (1945).Google Scholar
  11. 8.
    G. N. Lewis and M. Calvin, J. Amer. Chem. Soc. 67, 1232 (1945).Google Scholar
  12. 9.
    D. F. Evans, Nature 176, 777 (1955).Google Scholar
  13. 10.
    R. Lesclaux and J. Joussot-Dubien, J. Chim. Phys. 61, 1147 (1964).Google Scholar
  14. 11.
    N. J. Turro, J. Chem. Ed. 46, 2 (1969).Google Scholar
  15. 12.
    F. Perrin, Ann. Phys. (Paris) 12, 169 (1929).Google Scholar
  16. 13.
    W. L. Leoshin and L. A. Vinokurov, Physik. Z. Sowjet U. 10, 10 (1936).Google Scholar
  17. 14.
    C. A. Parker and C. G. Hatchard, Trans. Faraday Soc. 57, 1894 (1961).Google Scholar
  18. 15.
    P. P. Dikun, Zh. Eksperim. i Teor. Fiz. 20, 193 (1950)Google Scholar
  19. R. Williams, J. Chem. Phys 28, 577 (1958).Google Scholar
  20. 16.
    Th. Förster and K. Kasper, Z. Elektrochem. 59, 977 (1955).Google Scholar
  21. 17.
    B. Stevens and E. Hutton, Nature 186, 1045 (1960); Spectrochim. Acta 18, 425 (1962).Google Scholar
  22. 18.
    C. A. Parker and C. G. Hatchard, Trans. Faraday Soc. 59, 284 (1963); Proc. Chem. Soc., 147 (1962); Proc. Roy. Soc. (London) A 269, 574 (1962).Google Scholar
  23. 19.
    C. A. Parker, C. G. Hatchard, and T. A. Joyce, Nature 205, 1282 (1965).Google Scholar
  24. 20.
    C. A. Parker, Photoluminescence of Solutions, Elsevier Publishing Company, Amsterdam (1968).Google Scholar
  25. 21.
    J. D. Winefordner and P. A. St. John, Anal. Chem. 35, 2211 (1963).Google Scholar
  26. 22.
    H. Greenspan and E. Fischer, J. Phys. Chem. 69, 2466 (1965).Google Scholar
  27. 23.
    J. B. Birks and D. J. Dyson, Proc. Roy. Soc. A 275, 135 (1963).Google Scholar
  28. 24.
    J. B. Birks, Photophysics of Aromatic Molecules, Wiley-Interscience, London (1970).Google Scholar
  29. 25.
    D. F. Evans, J. Chem. Soc., 1351 (1957).Google Scholar
  30. 26. (a)
    H. Tsubomura and R. S. Mulliken, J. Amer. Chem. Soc. 82, 5966 (1960)Google Scholar
  31. (b).
    J. N. Murrell, Molec. Phys. 3, 319 (1960).Google Scholar
  32. 27. (a)
    K. Kawaoka, A. U. Khan, and D. R. Kearns, J. Chem. Phys. 46, 1842 (1967)Google Scholar
  33. (b).
    A. U. Khan and D. R. Kearns, J. Chem. Phys. 48, 3272 (1968).Google Scholar
  34. 28.
    S. P. McGlynn, T. Azumi, and M. Kasha, J. Chem. Phys. 40, 507 (1964).Google Scholar
  35. 29.
    G. W. Robinson, J. Mol. Spectrosc. 6, 58 (1961).Google Scholar
  36. 30.
    D. S. McClure, J. Chem. Phys. 17, 905 (1949).Google Scholar
  37. 31.
    M. Kasha, J. Chem. Phys. 20, 71 (1952).Google Scholar
  38. 32. (a)
    S. P. McGlynn, R. Sunseri, and N. Christodouleas, J. Chem. Phys. 37, 1818 (1962)Google Scholar
  39. (b).
    S. P. McGlynn, M. J. Reynolds, G. W. Daigre, and N. D. Christodouleas, J. Phys. Chem. 66, 2499 (1962)Google Scholar
  40. (c).
    N. D. Christodouleas and S. P. McGlynn, J. Chem. Phys. 40, 166 (1964).Google Scholar
  41. 33.
    A. P. Marchetti and D. R. Kearns, J. Amer. Chem. Soc. 89, 768 (1967).Google Scholar
  42. 34.
    G. Porter and M. W. Windsor, Proc. Roy. Soc. A 245, 238 (1958).Google Scholar
  43. 35.
    D. S. McClure, J. Chem. Phys. 19, 670 (1951).Google Scholar
  44. 36.
    R. Pariser, J. Chem. Phys. 24, 250 (1956).Google Scholar
  45. 37.
    S. D. Colson and E. R. Bernstein, J. Chem. Phys. 43, 2661 (1965).Google Scholar
  46. 38.
    J. Franck and G. Hertz, Verhandl Deut. Physik. Ges. 16, 457 (1914); Physik. Z. 17, 409 (1916).Google Scholar
  47. 39.
    E. N. Lassetre, Radiation Res., Suppl. 1, 530 (1959).Google Scholar
  48. 40.
    A. Kuppermann and L. M. Raff, J. Chem. Phys. 39, 1607 (1963)Google Scholar
  49. E. N. Lassitre, J. Chem. Phys. 41, 2971 (1966)Google Scholar
  50. J. R. Oppenheimer, Phys. Rev. 32, 361 (1928).Google Scholar
  51. 41.
    A. Kuppermann and L. M. Raff, Disc. Faraday Soc. 35, 30 (1963); J. Chem. Phys. 37, 2497 (1962).Google Scholar
  52. 42.
    A. Kuppermann, J. K. Rice, and S. Trajmar, J. Phys. Chem. 72, 3894 (1968).Google Scholar
  53. 43.
    M. A. Dillon, Creation and Detection of the Excited State, Vol. 1, A. A. Lamola, ed., Marcel Dekker, New York (1971), Chapter 8.Google Scholar
  54. 44.
    J. P. Doering, J. Chem. Phys. 51, 2866 (1969).Google Scholar
  55. 45. (a)
    W. G. Herkstroeter, A. A. Lamola, and G. S. Hammond, J. Amer. Chem. Soc. 86, 4537 (1964)Google Scholar
  56. (b).
    D. R. Arnold, R. L. Hinman, and A. H. Glick, reported in Advances in Photochemistry, Vol. 6 (1968), p. 328.Google Scholar
  57. 46.
    D. F. Evans, J. Chem. Soc., 1351 (1957); 3885 (1957); 2753 (1959); 1735 (1960); 1987 (1961).Google Scholar
  58. 47.
    R. E. Kellogg and W. T. Simpson, J. Amer. Chem. Soc. 87, 4230 (1965).Google Scholar
  59. 48.
    W. G. Herkstroeter and G. S. Hammond, J. Amer. Chem. Soc. 88, 4769 (1966).Google Scholar
  60. 49.
    A. A. Lamola, W. G. Herstroeter, J. C. Dalton, and G. S. Hammond, J. Chem. Phys. 42, 1715 (1965).Google Scholar
  61. 50.
    P. Wagner, J. Amer. Chem. Soc. 89, 2980 (1967).Google Scholar
  62. 51.
    G. Jackson and G. Porter, Proc. Roy. Soc. (London) A 260, 13 (1961).Google Scholar
  63. 52.
    A. Terenin and V. L. Ermolaev, J. Chim. Phys. 55, 698 (1958).Google Scholar
  64. 53.
    P. G. Bowers and G. Porter, Proc. Roy. Soc. (London) A 296, 435 (1967).Google Scholar
  65. 54.
    T. Medinger and F. Wilkinson, Trans. Faraday Soc. 61, 620 (1965).Google Scholar
  66. 55.
    A. A. Lamola and G. S. Hammond, J. Chem. Phys. 43, 2129 (1965).Google Scholar
  67. 56.
    L. M. Stephenson, Ph.D. Thesis, California Institute of Technology, Pasadena, California (1967).Google Scholar
  68. 57.
    C. A. Parker and T. A. Joyce, Chem. Comm., 234 (1966).Google Scholar
  69. 58.
    K. Sandros, Acta Chim. Scand. 23, 2815 (1969).Google Scholar
  70. 59.
    B. Stevens and B. E. Algar, Chem. Phys. Lett. 1, 58 (1967).Google Scholar
  71. 60.
    B. Stevens and B. E. Algar, Chem. Phys. Lett. 1, 219 (1967).Google Scholar
  72. 61.
    C. A. Parker and T. A. Joyce, Photochem. Photobiol. 6, 395 (1967).Google Scholar
  73. 62.
    C. A. Parker and T. A. Joyce, Chem. Comm., 108 (1966).Google Scholar
  74. 63.
    C. A. Parker and T. A. Joyce, Trans. Faraday Soc. 62, 2785 (1966).Google Scholar
  75. 64.
    I. V. Aleksandrov and K. K. Pukhov, Opt. Spectrosc. 17, 513 (1964)Google Scholar
  76. J. S. Brinen, J. Chem. Phys. 49, 586 (1968).Google Scholar
  77. 65.
    A. R. Horrocks and F. Wilkinson, Proc. Roy. Soc. A 306, 257 (1968).Google Scholar
  78. 66.
    R. E. Kellogg and R. G. Bennett, J. Chem. Phys. 41, 3042 (1964).Google Scholar
  79. 67.
    I. B. Berlman, Handbook of Fluorescence Spectra of Aromatic Molecules, Academic Press, New York (1965).Google Scholar
  80. 68.
    A. R. Horrocks, T. Medinger, and F. Wilkinson, in International Symposium on Luminescence. The Physics and Chemistry of Scintillators, N. Ruhl and H. Kallmann, eds., Verlag Karl Thiemig, Munich (1966).Google Scholar
  81. 69.
    M. W. Windsor and W. R. Dawson, Mol. Cryst. 4, 253 (1968).Google Scholar
  82. 70.
    R. G. Bennett and P. J. McCartin, J. Chem. Phys. 44, 1969 (1966).Google Scholar
  83. 71.
    A. R. Horrocks, T. Medinger, and F. Wilkinson, Trans. Faraday Soc. 62, 1785 (1966).Google Scholar
  84. 72.
    T. Medinger and F. Wilkinson, Trans. Faraday Soc. 62, 1785 (1966).Google Scholar
  85. 73.
    J. B. Birks, B. N. Srinivasan, and S. P. McGlynn, J. Mol. Spectrosc. 27, 266 (1968).Google Scholar
  86. 74.
    H. Labhart, Helv. Chim. Acta 47, 2279 (1964).Google Scholar
  87. 75.
    W. R. Dawson, J. Opt. Soc. Am. 58, 222 (1968).Google Scholar
  88. 76.
    W. Heinzelmann and H. Labhart, Chem. Phys. Lett. 4, 20 (1969).Google Scholar
  89. 77.
    B. Soep, A. Kellmann, M. Martin, and L. Lindquist, Chem. Phys. Lett. 13, 241 (1972).Google Scholar
  90. 78.
    G. Porter, Tech. Org. Chem. 8, 1081 (1961).Google Scholar
  91. 79.
    N. J. Turro, Molecular Photochemistry, Benjamin, New York (1965).Google Scholar
  92. 80.
    R. Li and E. C. Lim, J. Chem. Phys. 57, 605 (1972).Google Scholar
  93. 81.
    M. R. Wright, R. P. Frosch, and G. W. Robinson, J. Chem. Phys. 33, 934 (1960).Google Scholar
  94. 82.
    M. R. Wright, R. P. Frosch, and G. W. Robinson, J. Chem.Phys. 38, 1187 (1963).Google Scholar
  95. 83.
    E. C. Lim, J. Chem. Phys. 36, 3497 (1962).Google Scholar
  96. 84.
    G. W. Robinson and R. P. Frosch, J. Chem. Phys. 37, 1962 (1962).Google Scholar
  97. 85.
    R. E. Kellogg and R. P. Schwenker, J. Chem. Phys. 41, 2860 (1964).Google Scholar
  98. 86.
    D. P. Craig and I. G. Ross, J. Chem. Soc., 1589 (1954).Google Scholar
  99. 87.
    D. Ramsey, in Determination of Organic Structure by Physical Methods, F. C. Nachod and W. D. Phillips, eds., Academic Press, New York (1962), Vol. 2.Google Scholar
  100. 88.
    G. W. Robinson and V. E. DiGiorgio, Can. J. Chem. 36, 31 (1968); J. Chem. Phys. 31, 1678 (1959).Google Scholar
  101. 89.
    S. E. Hodges, J. R. Henderson, and J. B. Coon, J. Mol. Spectrosc. 2, 99 (1958).Google Scholar
  102. 90.
    A. D. Walsh, J. Chem. Soc., 2260 (1953).Google Scholar
  103. 91.
    J. C. D. Brand, J. Chem. Soc., 858 (1956).Google Scholar
  104. 92.
    G. W. Robinson, Can. J. Phys. 34, 699 (1956).Google Scholar
  105. 93.
    P. G. Wilkinson and R. S. Mulliken, J. Chem. Phys. 23, 1895 (1955).Google Scholar
  106. 94.
    R. S. Mulliken and C. C. J. Roothaan, Chem. Revs. 41, 219 (1947).Google Scholar
  107. 95.
    H. C. Longuet-Higgins, J. Chem. Phys. 18, 265 (1950).Google Scholar
  108. 96.
    S. P. McGlynn, T. Azumi, and M. Kinoshita, Molecular Spectroscopy of the Triplet State, Prentice-Hall, Englewood Cliffs, New Jersey (1969).Google Scholar
  109. 97.
    C. K. Ingold and G. W. King, J. Chem. Soc., 2702 (1953).Google Scholar
  110. 98.
    K. K. Innes, J. Chem. Phys. 22, 863 (1954).Google Scholar
  111. 99.
    J. H. Callomon and B. P. Stoicheff, Can. J. Phys. 35, 373 (1957).Google Scholar
  112. 100.
    J. Pancir and R. Zahradnik, Theoret. Chim. Acta (Berl.) 14, 426 (1969).Google Scholar
  113. 101.
    E. Gilmore, G. Gibson, and D. McClure, J. Chem. Phys. 20, 829 (1952); 23, 399 (1955).Google Scholar
  114. 102.
    Y. Konda and H. Sponer, J. Chem. Phys. 28, 798 (1958).Google Scholar
  115. 103.
    D. Olness and H. Sponer, J. Chem. Phys. 38, 1799 (1963).Google Scholar
  116. 104.
    V. Ermolaev and K. Svitashev, Opt. Spectrosc. 7, 399 (1959).Google Scholar
  117. 105.
    R. Kellogg and N. Wyeth, J. Chem. Phys. 45, 3156 (1966).Google Scholar
  118. 106.
    R. Bennett and J. McCartin, J. Chem. Phys. 44, 1969 (1966).Google Scholar
  119. 107.
    R. Borkman and D. Kearns, J. Chem. Phys. 44, 945 (1966).Google Scholar
  120. 108.
    V. Ermolaev and A. Terenin, Soviet Phys.—Uspekhi 3, 423 (1960).Google Scholar
  121. 109.
    J. Pitts, H. Johnson, and T. Kuwana, J. Phys. Chem. 66, 245 (1962).Google Scholar
  122. 110.
    R. Borkman and D. Kearns, J. Chem. Phys. 46, 2333 (1966).Google Scholar
  123. 111.
    A. Terenin and V. Ermolaev, Trans. Faraday Soc. 57, 1042 (1956).Google Scholar
  124. 112.
    N. C. Yang, P. McClure, S. Murov, J. Hauser, and R. Dusenbery, J. Amer. Chem. Soc. 89, 5466 (1967).Google Scholar
  125. 113.
    E. Baum, J. Wan, and J. Pitts, J. Amer. Chem. Soc. 88, 2652 (1966).Google Scholar
  126. 114.
    D. Murov, Ph.D. Dissertation, University of Chicago (1967).Google Scholar
  127. 115.
    W. Neeley and H. Dearman, J. Chem. Phys. 44, 1302 (1966).Google Scholar
  128. 116.
    B. Cohen and L. Goodman, J. Chem. Phys. 46, 548 (1962).Google Scholar
  129. 117.
    J. Paris, R. Hirt, and R. Schmitt, J. Chem. Phys. 34, 1851 (1961).Google Scholar
  130. 118.
    J. Brinen, J. Koren, and W. Hodgson, J. Chem. Phys. 44, 3095 (1966).Google Scholar
  131. 119.
    V. Ermolaev and I. Kotlyar, Opt. Spectrosc. 9, 183 (1960).Google Scholar
  132. 120.
    E. Lim and J. Yu, J. Chem. Phys. 45, 4742 (1966); 49, 3878 (1968).Google Scholar
  133. 121.
    J. Vincent and A. Maki, J. Chem. Phys. 39, 3088 (1963).Google Scholar
  134. 122.
    R. Harrell, Ph.D. Dissertation, Florida State University (1959).Google Scholar
  135. 123.
    J. Brinen, D. Rosebrook, and R. Hirt, J. Phys. Chem. 67, 2651 (1963).Google Scholar
  136. 124.
    R. Heckman, J. Mol. Spec. 2, 27 (1968).Google Scholar
  137. 125.
    V. Ermolaev, Opt. Spectrosc. 11, 266 (1961).Google Scholar
  138. 126.
    J. Longworth, R. Rahn, and R. Shulman, J. Chem. Phys. 45, 2930 (1966).Google Scholar
  139. 127.
    J. Drobnik and L. Augenstein, Photochem. Photobiol. 5, 13 (1966).Google Scholar
  140. 128.
    C. Helene, R. Santus, and P. Douzou, Photochem. Photobiol. 5, 127 (1966).Google Scholar
  141. 129.
    R. S. Becker, Theory and Interpretation of Fluorescence and Phosphorescence, Wiley-Interscience, New York (1969).Google Scholar
  142. 130.
    R. L. E. Drisko, Ph.D. Dissertation, The Johns Hopkins University (1968).Google Scholar
  143. 131.
    M. A. El-Sayed, Acc. Chem. Res. 1, 8 (1968).Google Scholar
  144. 132.
    W. Kauzmann, Quantum Chemistry, Academic Press, New York (1957).Google Scholar
  145. 133.
    G. W. Robinson and R. Frosch, J. Chem. Phys. 38, 1187 (1963).Google Scholar
  146. 134.
    S. K. Lower and M. A. El-Sayed, Chem. Rev. 66, 199 (1966).Google Scholar
  147. 135.
    S. P. McGlynn, T. Azumi, and M. Kinoshita, The Triplet State, Prentice-Hall, Englewood Cliffs, New Jersey (1969).Google Scholar
  148. 136.
    D. O. Cowan and R. L. E. Drisko, J. Amer. Chem. Soc. 92, 6281 (1970).Google Scholar
  149. 137.
    G. G. Giachino and D. R. Kearns, J. Chem. Phys. 52, 2964 (1970).Google Scholar
  150. 138.
    P. J. Wagner, J. Chem. Phys. 45, 2335 (1966).Google Scholar
  151. 139.
    P. J. Wagner and G. S. Hammond, J. Amer. Chem. Soc. 87, 4009 (1965); 88, 1245 (1966).Google Scholar
  152. 140.
    R. F. Borkman and D. R. Kearns, J. Chem. Phys. 46, 2333 (1967).Google Scholar
  153. 141.
    M. A. El-Sayed, J. Chem. Phys. 41, 2462 (1964).Google Scholar
  154. 142.
    D. Kearns and W. Case, J. Amer. Chem. Soc. 88, 5087 (1966).Google Scholar
  155. 143.
    M. A. El-Sayed, J. Chem. Phys. 38, 2834 (1963).Google Scholar
  156. 144.
    D. G. Carroll, L. Vanquickenborne, and S. P. McGlynn, J. Chem. Phys. 45, 2777 (1966).Google Scholar
  157. 145.
    C. Dijkgraaf and G. J. Hoijtink, Tetrahedron Suppl. 2, 179 (1963).Google Scholar
  158. 146.
    V. Ramakrishnan, R. Sunseri, and S. P. McGlynn, J. Chem. Phys. 45, 1365 (1966).Google Scholar
  159. 147.
    H. A. Benesi and J. H. Hildebrand, J. Amer. Chem. Soc. 71, 2703 (1949).Google Scholar
  160. 148.
    M. F. Thomaz and B. Stevens, in Molecular Luminescence, E. C. Lim, ed., Benjamin, New York (1969).Google Scholar
  161. 149.
    B. Stevens, in Advances in Photochemistry, Vol. 8, Wiley Interscience, New York (1971), p. 161.Google Scholar
  162. 150.
    H. Leonhardt and A. Weller, Ber. Bunsenges. Phys. Chem. 67, 791 (1963).Google Scholar
  163. 151.
    N. Matago, T. Okada, and K. Ezumi, Mol. Phys. 10, 203 (1966).Google Scholar
  164. 152.
    A. Weller, in Fast Reactions and Primary Processes in Chemical Kinetics, S. Claesson, ed., Wiley-Interscience, New York (1967), p. 413.Google Scholar
  165. 153.
    H. Beens, H. Knibbe, and A. Weller, J. Chem. Phys. 47, 1183 (1967).Google Scholar
  166. 154.
    H. Knibbe, K. Röllig, F. P. Schafer, and A. Weller, J. Chem. Phys. 47, 1184 (1967).Google Scholar
  167. 155.
    N. Matago, T. Okada, and N. Yamamoto, Chem. Phys. Lett. 1, 119 (1967).Google Scholar
  168. 156.
    J. B. Birks, M. P. Lamb, and I. H. Munro, Proc. Roy. Soc. (London) A 280, 289 (1964).Google Scholar
  169. 157.
    E. Döller and Th. Förster, Z. Phys. Chem. N.F. 34, 132 (1962).Google Scholar
  170. 158.
    J. Langelaar, R. P. H. Rettschnick, A. M. F. Lamboy, and G. J. Hoytink, Chem. Phys. Lett. 1, 609 (1967).Google Scholar
  171. 159.
    D. R. Scott and J. B. Allison, J. Phys. Chem. 66, 561 (1962).Google Scholar
  172. 160.
    G. Porter, Tech. Org. Chem. 8, 1055 (1961).Google Scholar

Copyright information

© Plenum Press, New York 1976

Authors and Affiliations

  • Dwaine O. Cowan
    • 1
  • Ronald L. Drisko
    • 2
  1. 1.The Johns Hopkins UniversityBaltimoreUSA
  2. 2.Essex Community CollegeBaltimoreUSA

Personalised recommendations