**Heat engine.**

[![crookes radiometer][1]][1]


  [1]: https://i.sstatic.net/chNDJ.gif
https://en.wikipedia.org/wiki/Crookes_radiometer#Thermodynamic_explanation

As has bene pointed out, a pigment is simply a molecule that absorbs or reflects light of a given wavelength.  A [photosynthetic pigment](https://ucmp.berkeley.edu/glossary/gloss3/pigments.html) is more than that - instead of just heating up the molecule absorbing it, light energy absorbed is transferred to an electron that can be passed along to ultimately participate in a chemical reaction and generate ATP.  This is a high hurdle for evolution and only a few such pigments are known to exist.

The OP asks for a microscopic structure.  I picture something bigger than a protein or molecule.  The structure could be something like the Crookes radiometer, pictured above.  These are a type of heat engine, turning electromagnetic energy into heat and from there into kinetic energy.

> Movement with black-body absorption When a radiant energy source is
> directed at a Crookes radiometer, the radiometer becomes a heat
> engine.[5] The operation of a heat engine is based on a difference in
> temperature that is converted to a mechanical output. In this case,
> the black side of the vane becomes hotter than the other side, as
> radiant energy from a light source warms the black side by black-body
> absorption faster than the silver or white side.

The mill will turn with any frequency that can heat the black side, and will turn in reverse if ambient surroundings are cooler than it is - [propelled now by blackbody radiation from the black side.](https://en.wikipedia.org/wiki/Crookes_radiometer#Movement_with_black-body_radiation)

WB stack has bandied about the idea of using kinetic energy (e.g. wind) to generate ATP.  Here heat energy is turned into kinetic energy which could be used to generate ATP which is nice because heat works on every molecular scale and you don't need to gear down captured energy as you would with wind.  Nanoscale heat engines exist and operate on the scale of the protein mechanisms that make ATP.  

A nanoscale heat engine is probably even a higher hurdle for evolution.  Less high for intelligent design!