Photophysical Effects in Model Systems

We are dealing with a highly ordered array of substances. What that array is on the molecular level—i.e., how the plane of the chlorin ring is located with respect to these layers or with respect to the spherical globules of which the layers seem to be composed—is still a matter of controversy and remains one of the areas which this writer would like to see the physical chemists explore. It is necessary to bridge the gap between ordinary statistical molecular behavior and individual structures that can be seen. We do not know, for example, what the arrangement of the chlorophyll molecules is in the lamellar layers. Order is, however, the major factor with which we are left. 

In order to develop this notion we undertook the model studies which will be discussed below, the determination of the electrical and 

The systems that were used by this writer and colleagues contained one of some four or five different donor molecules—phthalocyanine, violan-threne, perylene, etc.—we found that almost any highly aromatic system could serve as a conducting matrix and phthalocyanine was only one of these. The electron acceptor systems that we used were o-chloranil (the most commonly used), iodine and tetracyanoethylene. These donor and acceptor systems were used in various combinations. A pattern of results based on a conductivity cell is shown in Figs. 3a, b, and c. It is made of aquadag electrodes on which is coated the matrix (phthalocyanine or violanthrene, as the case may be) usually the samples are sublimed onto the electrode system. On top of the matrix is placed one of the doping agents, one of the donors or acceptors. 

In most of our work the matrices have been the donor molecules and the other part of the layer has been the acceptor molecules, which is either sublimed on top or sprayed on in a dilute benzene solution. These are the two principal ways in which the acceptor molecule is laid onto the donor. 

Electron spin resonance spectrum of o-chloranil doped phthalocyanine. Curve represents the first derivative of absorption. 

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