Naphtho[2,3-a]pyrene Thin Films – H,I, or J? Aggregate Alphabet Soup

Photon upconversion within the solid state has the potential to improve existing solar and imaging technologies due to its achievable efficiency at low power thresholds. However, despite considerable advancements in solution-phase upconversion, expanding the library of potential solid-state annihilators and developing a fundamental understanding of their solid-state behaviors remains challenging due to intermolecular couplings affecting the energy landscape. Naphtho[2,3-a]pyrene has shown promise as a suitable solid-state annihilator; however, the origin of the underlying emissive features remains unknown. To this point, here, we investigate NaPy/polymethylmethacrylate thin films at varying concentrations to tune the intermolecular coupling strength to determine its photophysical properties. The results suggest that the multiple emissive features present at room temperature arise from an I-aggregate (520 nm), an excimer (550 nm), and a strongly coupled J-dimer (620 nm).