Fluorescent molecular systems based on carborane-perylenediimide conjugates

This study presents the successful synthesis of two perylenediimide (PDI)-based ortho -carborane ( o -carborane) derivatives, PDI-CB1 and PDI-CB2 , through the insertion of decaborane into alkyne-terminated PDIs ( PDI1 and PDI2 ). The introduction of o -carborane groups did not alter the optical properties of the PDI units in solution compared to their carborane-free counterparts, maintaining excellent fluorescence quantum yields of around 100% in various solvents. This was achieved by using a methylene linker to minimize electronic interaction between PDI and o -carborane, and by incorporating bulky o -carborane groups at imide- position to enhance solubility and prevent π-π stacking-induced aggregation. Aggregation studies demonstrated that PDI-CB1 and PDI-CB2 have greater solubility than PDI1 and PDI2 in both nonpolar and aqueous solvents. Despite the steric hindrance imparted by the o -carborane units, the solid state emission of PDI-CB1 and PDI-CB2 was affected by aggregation-caused fluorescence quenching. However, solid PDI-CB1 preserved bright red excimer-type emission, which persisted in water-dispersible nanoparticles, indicating potential for application as a theranostic agent combining fluorescence bioimaging with anticancer boron neutron capture therapy (BNCT) due to its high boron content. o -Carborane-perylenediimide conjugates exhibit exceptional fluorescence properties in solution, while red-light excimer emission is observed in their aggregated forms and in dispersible nanoparticles.