Heteropentacyclic quinoxalino[2,3-b]phenoxazines: the synthesis, optoelectronic, and electrochemical properties.

A series of new derivatives comprising heteropentacyclic 12H-quinoxalino[2,3-b]-phenoxazine (QOPO) system and functionalized with arylamide anchoring groups was synthesized. Their photostability as well as the spectral, luminescent, electrochemical, and optoelectronic properties were studied both in composites prepared by adsorption of QOPO onto the TiO₂ surface and in solution. Attachment of the amide anchoring groups to the QOPO core provides high adsorption of the compounds and the onset of photovoltaic properties that were not observed in the unfunctionalized precursors. However, these groups do not provide efficient injection of excited electrons into the conduction band of the semiconductor. According to B3LYP/6-311++G(d,p) density functional calculations of the model nanoclusters QOPO/(TiO₂)₁₀, efficient electron injection and, as a consequence, high photovoltaic conversion efficiency of dye-sensitized solar cells require delocalization of the LUMO of the QOPO/TiO₂ system over both structural fragments. Relevant anchoring groups are proposed. [ABSTRACT FROM AUTHOR]