1) Download Introduction which is Introduction to the History of Photochemistry from the Neckers blue book. Get some of the articles in this book from the following links.

2) "Characterization of Electronic Transitions in Complex Molecules"
Kasha proposed "Kasha's rule" in this paper.
Michael Kasha |  Pg 14-19 |  Download PDF

3) "Phosphorescence and the Triplet State"
G. N. Lewis and Kasha proposed the triplet state existed and was responsible for the emission we now call phosphorescence in this paper.
Gilbert N. Lewis and M. Kasha |  Pg 132-150 |  Download PDF

4) "Phosphorescence in Fluid Media and the Reverse Process of Singlet-Triplet Absorption"
Singlet-triplet absorption was identified as the inverse of triplet-singlet emission in this paper.
Gilbert N. Lewis and M.Kasha |   Pg 151-160 |  Download PDF

5) "Photomagnetism. Deternination of the Paramagnetic Susceptibility of a Dye in Its Phosphorescent State"
The triplet state of fluorescein is shown to be paramagnetic in this paper.
G.N. Lewis, M. Calvin and M.Kasha |  Pg 804-812 |  Download PDF

6) "Four great personalities of science: G. N. Lewis, J. Franck, R.S. Mulliken and A. Szent-Gyorgyi"
Michael Kasha |  Pg 1615-1622 |  Download PDF

7) "The Triplet State"
An example of G.N. Lewis' Research Style
Michael Kasha |  Pg 204-815 |  Download PDF

8) "Mechanisms of Photoreactions in Solutions. I. Reduction of Benzophenone by Benzhydrol"
William M. Moore, George S. Hammond and Robert P. Foss |  J. Am. Chem. Soc., Volume 83 |  Pg2789-2794 | Download PDF

9) "Some Remarks about Free Radicals and The Photochemistry of Solutions"
J. Franck and E. Rabinowitsch |  Transactions Faraday Society, 30(1934) |  Pg 120-131 |  Download PDF

10) "The Collison Mechanism and The Primary Photochemical Process in Solutions"
E. Rabinowitch and W. C. Wood |  Trans. Faraday Soc., vol 32(1936) |  Pg1381-1387 |  Download PDF

11) "Kinetics of Competitive Processes when Reactive Fragments are Produced in Pairs"
Richard M. Noyes |  J. Am. Chem. Soc, 77(1955) |  Pg 2042-2045 |  Download PDF

12) "From Jablonski to Femtoseconds. Evolution of Molecular Photophysics"
M. Kasha |  ACTA Physica Polonica A, vol 95(1999) |  Pg 15-36 |  Download PDF