In this chapter, photonic crystal structures in plants and animals are reviewed. From the perspective of materials science, they can be considered as hybrid nanostructured material systems, comprising inorganic and organic components with appropriate refractive index contrast. General principles of structure formation, the influence of disorder, and possible biological functions are elucidated. Giving examples from the most important and well-investigated taxa, the occurring material combinations and composite structures are presented. Actual trends in biophotonic crystal research that arise interest for applications in materials science are the investigation of photonic glasses and the preparation of naturalartificial hybrid structures with combined properties for the manipulation of light.

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Understanding phase separation phenomena in blends of organic electron acceptor and donor materials is of special interest in the context of organic optoelectronic applications. In this study, we focus on the phase behavior of a special class of spiro-linked compounds, which serve as model systems for morphological control in phase-separated small-molecule electron donor–acceptor blends. Thermal analysis and quantitative image analysis were the key techniques for developing a suitable approach for modeling the phase diagram with minimal material consumption. We report an uncommon miscibility gap in the liquid and glassy phase and show that the phase diagram can be modified by addition of a third, ambipolar compound in analogy to ternary A/B/AB polymeric blends. For an exemplary ternary system, a bicontinuous morphology with a pattern length scale of a few tens of nanometers was realized in the bulk that verifies the applicability of this approach to morphology control.