Structure-based color of natural petals discriminated by polymer replication.

The optical appearance of many flowers in nature relies on their inherent pigments ("chemical color") as well as on the surface structure of the epidermis ("structural color"). The structural color is created by a combination of regular and irregular micro- and nanosized features. With a red rose petal as a biological template, we have separated the structural coloration from the chemical coloration by reproducing the petal's intricate surface structure in a pigment-free polymer. UV-vis reflectance measurements of the templates showed that the pigment-induced chemical coloration of the red-rose petal results in intense absorption and reflection in the green (∼550 nm) and red (∼700 nm) spectral region, respectively. The micro- and nanosized structural hierarchy on the petal surface, on the other hand, induced a modulation of the optical reflectivity and a filtering effect in specific wavelength ranges. More notably, we observed that a variation in the size of the micro/nanostructures on the petal surface leads to an effective modulation of the reflectance. These results could provide useful tips for the design of bioinspired optical devices, emulating natural petal structures.