You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

π-Extended isomeric and expanded porphyrins. The phenomenon of π-extension has been widely applied to, and exploited within, the field porphyrin chemistry. The development of reliable synthetic routes to various useful starting materials has facilitated the underlying preparative work. The chemical resemblance between porphyrins and expanded and isomeric porphyrins, as well as the increasing accessibility of the requisite starting materials is giving birth to the hybrid field of π-extended expanded and isomeric porphyrins. This tutorial review is intended to provide an overview of up-to-date published synthetic efforts and to summarize the effect of annulation on the properties of expanded and isomeric porphyrins.
{"Chemical": ["porphyrins", "porphyrin"]}