Metastable 9‐Fluorenone: Blueshifted Fluorescence, Single‐Crystal‐to‐Single‐Crystal Reactivity, and Evaluation as a Multimodal Fingermark Visualization Treatment

A metastable form of 9‐fluorenone (MS9F) has been characterized using Raman spectroscopy, fluorimetry, and X‐ray diffraction techniques. MS9F emits blue fluorescence (λmax=495 nm) upon 365 nm irradiation and undergoes a single‐crystal‐to‐single‐crystal (SCSC) transformation to reach the ground state form (GS9F) over approximately 30 minutes, whereupon it emits the expected green fluorescence. A structure–property relationship for this fluorescent behavior has been posited. MS9F and GS9F were applied as a means of visualizing latent fingermarks on a nonporous surface. This approach identified three different modes of fluorescent fingermark visualization using 9‐fluorenone. The unexpected discovery of two unique emissive forms of 9‐fluorenone after using it to treat latent fingerprints (see figure) has resulted in the characterisation of a new metastable polymorph. This species exhibits single‐crystal‐to‐single‐crystal reactivity, blue‐shifted fluorescent emission, and potential forensic applications.