A DOI (Digital Object Identifier) is a permanent link to a scholarly work. The ACS Style Guide recommends including a DOI whenever one exists, because it is more stable than a publisher URL.
Correct DOI format in ACS
Format the DOI as a full URL: https://doi.org/10.1021/jacs.0c01234. Do not add a period after the DOI if it ends the reference entry —ACS convention typically ends the sentence before or includes the DOI as the final element.
Example journal reference: Smith, J. A.; Jones, B. C. Article Title. J. Am. Chem. Soc. 2024, 146 (3), 1234–245. https://doi.org/10.1021/jacs.3c12345.
When no DOI is available
For older print-only articles, omit the DOI and use page numbers. For websites and some reports, use the full URL plus an access date in parentheses.
Never invent a DOI. If CrossRef does not resolve the identifier, leave it out or confirm with the original publisher record.