Tuning exciton delocalization in organic crystalline thin films

Organic electronics have been drawing a lot of attention over the past few decades with recent commercial applications such as organic photovoltaics, OLEDs, and flexible organic displays. One of the key components for designing organic molecules suitable for electronic devices is a fundamental understanding of excitonic behaviors. Here we report on the fabrication and photoluminescence studies of crystalline thin film organic alloy systems, metal free and metal based octabutoxyphthalocyanine (MOBPc x H 2 OBPc 1-x ), and metal-free H 2 OBPc and octabutoxynapthalocyanine (H 2 OBNc) mixtures (H 2 OBNc x H 2 OBPc 1-x ). Crystalline thin films of these materials were deposited using an in-house developed pen writing technique that results in macroscopic long-range order even at the ratio of x = 0.5, which is unique and important for spectroscopic studies. Our experiments reveal that the coherent excitonic states of MOBPc x H 2 OBPc 1-x and H 2 OBNc x H 2 OBPc 1-x crystalline thin films can be tuned continuously as a function of alloy concentration (0 < x < 1). Moreover, the solution-processed technique used to fabricate these crystalline thin films provides us an unprecedented advantage in designing and controlling the bandgap tunability as well as achieving the desired exciton coherent length for variety of applications.