Question

how does photon energy change with increasing frequency?

Answer 1

are you asking for an expression or are you asking why it happens?

Answer 2

If you are asking for an expression, then here it is: \[E=h \times \nu\] where E is the Photon Energy, h is plank's constant (6.626068 × 10-34 m2 kg / s) and ν is the frequency.

In other words, frequency is directly proportional to energy. Plank's constant can be used to convert between the two.

As for why this is true? I doubt anyone knows for sure. Photons are directly related to atomic energy states. There frequency is directly related to the quantum levels in the atomic structure. Larger jumps by a particle between these energy states, produce photons of higher frequency and vice versa. It's how the Universe is structured. And, perhaps it's that way because no other way could produce a stable Universe -- which is why the Universe exists -- 'cuz otherwise it would have burst into existence only to rapidly collapse, or expand to oblivion in short order. Who knows how long this process has been going on. Perhaps, before this Universe came into being, many others flashed in and out. It wasn't until this one happened, and stuck around for some 15 billion years, that life could get a foot hold and start asking the question ;)