Luminescence of N²,3-etheno-2-aminopurine Embedded in Polyvinyl Alcohol Films at Room Temperature

The luminescence properties of N²,3-etheno-2-aminopurine (N²,3-ε2APu) have been studied using steady-state and time-resolved spectroscopy. N²,3-ε2APu was embedded in poly(vinyl alcohol) (PVA) polymer, which is known for effective immobilization of dissolved fluorophore molecules. Upon UV excitation, N²,3-ε2APu shows a bright dark-blue fluorescence with high fluorescence anisotropy, indicating efficient immobilization. Time-resolved fluorescence measurements show a somewhat heterogeneous lifetime, requiring a lifetime distribution model to fit the data. The fit reveals a central lifetime of about 5 ns and a half-width of the Lorentzian distribution of about 2 ns. We attribute this lifetime spread to the varying surroundings of fluorophore molecules in the polymer matrix. The N²,3-ε2APu-doped PVA films exhibit strong room-temperature phosphorescence (RTP) centered at 500 nm, with a lifetime of approximately 0.15 s. The excitation at 330 nm results in negative phosphorescence anisotropy. Interestingly, N²,3-ε2APu-doped PVA films can be directly excited to a triplet state at longer wavelengths (above 400 nm). This excitation results in a high positive phosphorescence anisotropy, reaching a value of 0.3 at about 450 nm. The ability to excite a molecule at longer wavelengths may find applications in the biomedical sciences, particularly in the study of photo-chemically labile proteins and their complexes with emitting ligands.