The effect of spin–orbit coupling on selenadiazolo- and thiadiazolo- fused 1,10-phenanthrolines

• Phenanthroline derivatives with chalcogens and their photophysics were investigated.
• The ligand PhenSe presents room temperature phosphorescence.
• A heavy-atom effect in phenanthroline derivatives is evidenced.
• PhenSe presents high photocurrent and long lifetime.

Phenanthroline derivatives have been widely studied for many practical applications, and when fused with either a selenadiazole or a thiadiazole unit and used as ligands to produce metal complexes such complexes present unique photochemical and magnetic properties. In this work, a detailed theoretical description (using computational methods) of the electronic structure of these ligands is presented to explain their different photochemical and photophysical properties. In particular, the heavy atom effect on the spin–orbit coupling has a major influence on transitions between the excited states of [1,2,5]selenadiazolo[3,4-f][1,10]phenanthroline and the appearance of phosphorescence under inert argon atmosphere at room temperature. Photocurrent experiments demonstrated that these specific properties of the [1,2,5]selenadiazolo[3,4-f][1,10]phenanthroline are promising for photovoltaic applications.

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