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Prof. L. C. Kimerling Department of Materials Science and EngineeringMaterials Processing Center Massachusetts Institute of Technology 77 Massachusetts Ave, Cambridge, MA, 02139, USA Dr. J. Michel Materials Processing Center Massachusetts Institute of Technology 77 Massachusetts Ave, Cambridge, MA, 02139, USA Prof. E. L. Thomas Department of Mechanical Engineering and Materials Science Rice University 6100 Main Street, Houston, TX, 77005, USA E-mail: elt@rice.edu

plays, [11] sensors [12] and molecular probes. [13] Another easy approach to dye emission color tuning takes advantage of solvatochromism. [14] Polar dyes in particular can be sensitive to the properties of their surroundings. The polarity or dielectric constant of the local medium, whether liquid [15] or solid state, [16,17] can affect the ground state or excited state energies of fluorophores. [18,19] In fact, intermolecular interactions are not restricted to fluorophores and solvents. For polar dyes, fluorophore‐fluorophore (F‐F) interactions can be so significant that their emission spectra may be adjusted with concentration. For example, emission from the laser dye DCM2 can vary from yellow to red when the relative concentration of DCM2 in TPD thin films changes from 0.9‐11wt%. [16] Polyester side chain grafted poly(aryleneethynylene)s also display different solid state emission colors as a function of the polyester/conjugated polymer dye ratio. [20] Recently, a single dye species was used to generate multicoloremissionon pre-patternedsolidsubstrates,basedon the transition energy differences associated with different dye aggregation states. [7] These are examples of luminescence