The couple transformed chemistry into a modern science.

Literal

Husband-and-wife [topic-は] chemistry [object-を] modern-science [toward-へと] completely-changed.

一変させた is the causative of 一変する ('to change completely'): 'made it change completely.' へと combines direction へ with the quotative/resultative と. Likely refers to the Curies or Lavoisiers.