I did some reading the other day on the subject, because evolution was kind of my thing in college. I love learning this stuff.
So when plants were first starting to evolve (the first green algaes), most of the photosynthetic organisms were bacteria using a molecule called bacteriorhodopsin. Bacteriorhodopsin soaks up most of the visible light spectrum (reflecting blue and red light, the far ends of the spectrum, thus appearing purple), and its mechanism for generating energy is fundamentally different than chlorophyll. Bacteriorhodopsin is a proton pump. It essentially moves protons across a membrane against the concentration gradient. This proton gradient is then eventually converted into chemical energy. The process of bacteriorhodopsin is inefficient because it takes two energy conversion steps. Photons are converted into kinetic energy, and the kinetic energy is converted into chemical energy. This is why it soaks up such a large amount of the visible spectrum.
Chlorophyll, due to the fact that most of the available light was taken, had to be more efficient. It uses the sun’s energy to excite electrons instead, and uses these excited electrons to perform endothermic reactions. The process is a single conversion (light into chemical energy), and thus significantly more efficient.
I don’t think there would be much benefit genetically engineering bacteriorhodopsin into plants, because the mechanisms of energy generation are too different, and the plants might absorb too much light energy as a result, spontaneously combusting.
(FYI, this is oversimplified, the chemistry is way more complicated. But it is fairly accurate representation)