Why does glass not permit long wavelength infrared to pass through?
Certain glass (fused silica) can!
You might want to start by reading the FAQ in the General Physics forum. The entry on photon speed through a solid might be relevant.
So there is no classical explanations but you need to invoke quantum theory?
No, you need to invoke the property of the material! And that will require knowledge of solid state physics.
can give me an idea about the properties of fused silica
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