Earlier reports on rod-like conjugated molecules of similar shape and size such as α-sexithiophene (6T) and para-sexiphenyl (6P) indicated mixed crystal growth in equimolar blends. The spectral overlap between the 6P fluorescence and 6T absorption might there give rise to resonant energy transfer between the two species. In marked contrast to H-type aggregation found for 6T bulk crystals, isolated monolayers of 6T as well as 6T monolayers sandwiched between 6P multilayers have been reported to show pronounced green (instead of red) fluorescence, which has been attributed to J-type aggregation. Here, we investigate whether these altered optical properties of 6T translate from the monolayer to a bulk equimolar blend with 6P. Insight into the mixed crystal structure for vacuum co-deposited films of 6T + 6P is provided by using synchrotron grazing-incidence x-ray diffraction on different substrates. By correlating the optical properties of the pure and the mixed systems using absorption and photoluminescence spectroscopy we identify the green emission known from 6T monolayers to prevail in the blend. Our analysis indicates the formation of aggregates which are promoted by the molecular arrangement in the mixed crystal structure highlighting that the remarkable optical properties of 6T/6P heterostacks translate into mixed crystalline films. This study underlines that tuning the opto-electronic properties of organic semiconductors by blending species of similar shape but distinct opto-electronic properties is a promising pathway to achieve altered material properties.

早期关于类似形状和大小的棒状共轭分子的报道，例如 α-六联噻吩 (6T) 和对联苯 (6P) 表明等摩尔混合物中的混合晶体生长。6P 荧光和 6T 吸收之间的光谱重叠可能会引起两种物质之间的共振能量转移。与 6T 块状晶体的 H 型聚集形成鲜明对比，据报道，6T 的孤立单层以及夹在 6P 多层膜之间的 6T 单层显示出明显的绿色（而不是红色）荧光，这归因于 J 型聚集. 在这里，我们研究了 6T 的这些改变的光学特性是否会从单层转化为与 6P 的大量等摩尔混合物。通过在不同基板上使用同步加速器掠入射 X 射线衍射，可以深入了解 6T + 6P 真空共沉积薄膜的混合晶体结构。通过使用吸收光谱和光致发光光谱关联纯系统和混合系统的光学特性，我们确定了 6T 单层已知的绿色发射在混合物中占主导地位。我们的分析表明，混合晶体结构中的分子排列促进了聚集体的形成，突出表明 6T/6P 异质堆叠的显着光学特性转化为混合晶体薄膜。这项研究强调，通过混合形状相似但光电特性不同的物种来调整有机半导体的光电特性是实现改变材料特性的有希望的途径。