Spectroscopic observation of conformation-dependent charge distribution in a molecular cation

A prototypical case of a molecular radical cation is reported whose electrostatic charge distribution is determined entirely and uniquely by its conformational structures. Experimental observation of charge distribution in a molecular ion was for the first time demonstrated to be feasible by optical spectroscopy in the case of L-phenylalanine cation by utilizing the fact that its photodissociation propensity is entirely determined by the electronic character of its charge distribution. The cationic charge was explicitly shown to be localized in a single site or two different sites depending on the molecular conformation.