The phrase “pure energy” doesn’t have much use in physics, but yes, mass-energy equivalence does essentially predict that mass can be transformed into energy, and energy into mass.
The principle of mass-energy equivalence, which Einstein wrote about starting in 1905, predicts that, contrary to the old principles of conservation of mass and conservation of energy, the invariant (AKA rest) mass of a collection of bodies can be change, as can their kinetic energy, but that their relativistic, (or effective) mass times the speed of light squared ([imath]mc^2[/imath]) cannot. In short, it replaces the principle of conservation of mass and energy with one of conservation of a single, combined quantity, mass-energy.
This theory is pretty intuitive when used on systems where every body has non-zero rest mass and speed less than c: it essentially says that when a body’s speed is increased, its mass increases also. It gets some counterintuitive in systems with bodies with zero mass that move at c, as the photon is theorized to do in quantum mechanics and other theories.
You can, in principle and in practice, transform zero rest mass, speed of light-traveling photons into non-zero rest mass, slower than light “matter”. But when people say something is a “basic” or “constituent” part of something else, they usually don’t mean that it can be transformed into the new stuff, but that the new stuff contains it.
No particle “contains” photons, in the sense that protons contain quarks and gluons, or atomic nuclei contain protons and neutrons.
Practically, you can’t create “matter particles” more massive than electrons from photons, because there are not photons, nor any known means of creating ones with enough energy. For example, to create a proton – antiproton pair, you’d need to have a photon with at least 2 GeV, about 2000 times more than the most energetic known ones.
As LB noted, the photon has zero charge. Perhaps you’re thinking of the electron, an entirely different particle?
isn't a photon and an electron basically the same thing?
one is bound to a nucleus of an atom, one isn't, and it is flowing in the space
and while it interacts with matter it is transduced to different wavelengths and the such?