Isomeric Dibenzodiindenophenanthrene Diradicaloids: Synthesis, Structures, Properties, and Efficient NIR Photothermal Conversion for Imaging

Abstract

ABSTRACT Structural isomerism is a powerful strategy to modulate the fundamental properties of organic diradicaloids. Herein, we report the synthesis and characterization of a series of isomeric open‐shell polycyclic hydrocarbons (PHs) ( 1 – 3 ) based on the dicyclopenta[ b , j ]phenanthrene framework, whose diradical properties are compared with those of their anthracene‐based isomers. Combined experimental and theoretical studies reveal that subtle structural isomerism dictates their distinct electronic structures and properties, featuring large diradical characters ( y 0 = 0.54–0.72), small singlet‐triplet energy gaps (Δ E S‐T = −0.99 to −2.79 kcal/mol), and narrow HOMO‐LUMO energy gaps (0.90–1.16 eV). They exhibit remarkable multistage reversible redox behaviors, forming stable radical cations, radical anions, dications, and dianions, with the dicationic structures unambiguously confirmed by x‐ray crystallographic analysis. Notably, compounds 1 – 3 display fast responses to near‐infrared (NIR) laser irradiation, along with excellent photothermal (PT) stability, good PT conversion efficiency and high‐quality PT imaging performance. This work not only provides deep insights into the structure–property relationships of isomerism‐engineered diradical PHs but also establishes a robust molecular platform for advanced NIR PT materials.