Hypericin is a polycylic quinone. It has four hydroxyl groups that are very near to two carbonyls. Due to this arrangement the molecule is a likely candidate for proton or hydrogen atom transfer: that is, the hydrogen atom may at any time be found on one or the other oxygen. Such a process is known to occur, upon light absorption, in other molecules whose hydroxyl and carbonyl groups are in close proximity .
We study hypericin (and its analogs) by exciting it with pulsed lasers of different wavelengths (colors) in order to observe its behavior in its excited state, as a function of time. This technique is called time-resolved spectroscopy and is used to understand primary chemical processes.
We have shown several important things about hypericin. They are:
1) Hypericin undergoes excited state proton transfer (or atom transfer), despite the mirror image symmetry of the absorbance and emission spectra.
2) This proton or atom transfer is mediated not by the solvent but by internal vibrations and motions of the molecule and shows no deuterium isotope effect. This behavior is quite different from most other molecules undergoing such and excited-state transfer reaction.
3) Hypercin ejects a proton when it is excited. This results in an acidification of its surroundings. This may play a critical role in its antiviral and antitumor activity.