Design, synthesis and optical properties of small molecules based on dithieno[3,2-b:2′,3′-d]stannole and stannafluorene

In this paper, a series of stable Sn-containing heteroaromatic conjugated oligomers, dialkyl dithieno[3,2-b:2',3'-d]stannole (DTSn) and stannafluorene (SnF) derivatives, were designed and synthesized employing a new synthetic route. The distinctive feature of this route is that terminal groups are linked to the backbone before the stannole cycle closed, which can avoid the cleavage of stannole in the Stille reaction. Three Sn-heteroaromatic small molecules, DTSn-1, SnF-1 and SnF-3, have been obtained and characterized. The density functional theory (DFT) calculations show that the alkyl groups are further displaced from the conjugated backbone due to the larger atomic radius of Sn, which allows a stronger p-stacking interaction to occur. Interestingly, the fluorescence intensity of DTSn-1 is increased in the presence of Al3+ due to interaction between Al3+ and Sn. However, the emissions of the three Sn-containing oligomers can be quenched by Ru3+, which renders these compounds potential candidates as fluorescence detectors for Ru3+.