Herapathite
Bart Kahr,*
John Freudenthal,
Shane Phillips,
Werner Kaminsky
Herapathite crystals were first prepared when an assistant to
the toxicologist Herapath mixed iodine with the urine of a quinine-fed
dog. Herapath was shocked when his transparent crystals sitting
one atop the other at right angles were "black as midnight"
and predicted that they would replace costly mineral polarizers.
Such a change in practice in optics had to await Land, who oriented
fragile herapathite microcrystals in extruded polymers, a process
that produced the first large-aperture light polarizers and,
in turn, the Polaroid empire. Curiously, the crystal structure
of herapathite has never been established, and thus its chromophore
and mechanism of action remain a mystery. The single crystal
structure of herapathite is herein established, and its complete
dichroism can be attributed to delocalized excitations along
...I
3-...I
3-... chains. The workings of herapathite, one of
the most successful serendipitously engineered crystals, is
only now understood.
* To whom correspondence should be addressed. Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, USA. E-mail: bart.kahr{at}nyu.edu
