Room temperature phosphorescence: investigation into external perturbation of PVA film to enhance spin-orbit coupling

Abstract

In this thesis, we present the Room Temperature Phosphorescence (RTP) of 4’-6-diamidino-2-phenylindole (DAPI) and Coumarin 106 (C106) embedded in PVA poly ((vinyl)alcohol) film, respectively. Our previous studies concluded that chromophores are perturbed significantly enough to exhibit efficient phosphorescence emission when embedded into the PVA film. Furthermore, we observed that for some compounds embedded into the PVA film, we can observe direct triplet state excitation followed by strong phosphorescence emission. We also noticed that phosphorescence efficiency depends on PVA film preparation. So, we want to investigate modifications in PVA preparation/treatment and how the modifications may enhance Spin-Orbit Coupling (SOC). Our long-term project goal is to investigate if external conditions (conditions we can control/change externally, like electromagnetic fields) can affect SOC and lead to RTP emission in liquid solutions. We found that an efficient room temperature phosphorescence (RTP) of DAPI has been observed with UV and blue light excitations. For C106, we also found an efficient RTP. We observed C106 directly excited phosphorescence at 465 nm, well outside the absorption band. Then, we used C106 samples to study the effects of external modifications to the PVA treatments. We found that the PVA polymer films change their optical properties after annealing at higher temperatures. Whereas the fluorescence intensity of C106 in PVA films modestly decreases with annealing, the phosphorescence depends dramatically and progressively increases by many folds. We believe this increase in the phosphorescence intensities results from increased intersystem crossing (ISC), which also decreases fluorescence. The phosphorescence lifetime decreases with annealing while the phosphorescence intensity increases. We could not confirm the validity of investigating any external conditions that can affect SOC. However, we feel confident in our initial findings with annealing to say that it is possible to manipulate the PVA film preparation/treatment to enhance SOC.