Although optical dichroism is known for molecular crystals , the design of such crystals using differently functionalized channels as shown here potentially offers a wide range of color-to-color transitions. We also included methyl orange (MO), or 7,7,8,8-tetracyanoquinodimethane lithium salt (TCNQ) in crystals saturated with sodium fluorescein (SF) (Figures ). The scope of this self-assembly process was further demonstrated by size-selective functionalization of the different nanosized channels of the host crystals with the sodium salts of fluorescein isothiocyanate isomer I (FITC) and resorufin (SR) (Figure ). The crystals functionalized with TCNQ and SF, and FITC and SR are also dichromic (e.g., green-yellow, bordeaux-orange).