I feel like I’ve been neglecting the blog a bit lately, but now that finals are over posts should get a little more substantial. How about a nice JACS article on chemiluminescence to “brighten” your day?
Isobe et al. have written a nice paper that brings together all kinds of theoretical calculations of the chemiluminescent reaction of luciferins with triplet oxygen. This one’s not for the faint of heart (several pages long), but a few sections are pretty fascinating, particularly their study of controlling spin-orbit coupling (SOC) by modulating the extent of protonation of luciferin peroxides, intermediates in the reaction. Spin-orbit coupling lowers the photonic quantum yield of chemiluminescent reactions by essentially “siphoning off” light-emitting singlet molecules into the lower-energy, non-emitting triplet state before they can emit light. The group determined that the extent of SOC was dependent on the position of the transition state of the O-O elongation process–very late and very early TS’s both led to strong SOC, while weak SOC was observed somewhere in the middle. They then correlated the position of the transition state with the extent of protonation of the luciferin peroxide, and from there concluded that changing the extent of protonation of luciferin peroxides changes the quantum yield of the luciferin + triplet oxygen reaction.
So pretty much, in conclusion, light emission is a function of pH. Neat eh? Perhaps a new pH meter concept there?