Control of crystal morphology of a fluorescent charge transfer complex by dewetting on a mica surface

By changing simple experimental parameters, the receding speed of a droplet and the concentration of solutes, we were able to control the nanoscale morphology of fluorescent charge transfer complex of pyrene and tetracyanobenzene. Dilute solutions of pyrene and tetracyanobenzene were allowed to evaporate during roller-assisted casting on glass or mica substrates. In 1:1 mixtures, fibrous crystals with a width of a few μm and an aspect ratio of more than 100 were obtained with 5 mM solutions. The effects of roller speed, solute concentration and donor to acceptor ratios on the fiber formation were studied. Optical microscopy, fluorescence microspectrometry, and scanning nearfield optical microscopy were used to characterize the resulting fibers and crystals.