• Gravitationally.
• Conversion to matter-antimatter pairs.
• In non-linear optical media, which is technically all substances, but effect strength varies.
Of course electrons are involved in the last of those, but not in the way you mean. Non-linear optical media electrons remain bound to their atoms, and act by orbital resonance effects.
The last of those is a realistic path to a general-purpose photonic computer. I worked on a design for one, and I was surprised to find our design would run not much faster than a good electronic computer, while being larger, due to optical wavelengths. But it may have been more energy efficient if we'd built it. Or rather, the calculation part may have been more efficient, with memory being less efficient than transistors. Also we didn't spend much time optimising it.
Small photonic machines are good for particular calculations such as energy-efficient FFTs, but that is smaller scale than a general purpose processor.
(If anyone is interested in photonic computer design, feel free to get in touch!)