Chemical structure and composition of the investigated spirobifluorene copolymers. The contents of each unit are as follows: spirocopolymer 1 (, , and ) and spirocopolymer 2 (, , and ).
Normalized room temperature prompt fluorescence spectrum of a thin film of spirocopolymer 1 excited at 3.49 eV (355 nm) with an intensity of and normalized absorption of a thin film.
Prompt room-temperature PL emission spectra of thin polymer films of spirocopolymer 1 (solid line), spirocopolymer 2 (dotted line), and polyfluorene (PF) (dashed line) doped with 2-wt % PtOEP upon excitation into the PtOEP singlet at 537 nm (2.31 eV) with an excitation intensity of . The spectra were measured with a gate window of 10 ms. Since film thickness and doping level of all samples were identical, the detector counts can be used as a measure to compare the upconversion intensity. An interference filter was used to suppress the green laser light and a short-pass filter to cut the intense PtOEP phosphorescence.
Intensity dependence of PtOEP phosphorescence and upconverted blue delayed fluorescence (DF) from the matrix polymer of a thin film of spirocopolymer 1 doped with 0.5-wt % PtOEP. Excitation was performed at 537 nm (2.31 eV) at room temperature. ( denotes the slopes of each line which is a guide to the eye.)
PL emission spectra of thin films of spirocopolymer 1 doped with 0.5-wt % PtOEP (solid line) and 1.0-wt % PtOEP (dashed line). Excitation was performed at 537 nm with at room temperature. An interference filter was used to suppress the intense green laser peak.
Schematic representation of the energy levels and transfer mechanism in the PtOEP-doped spirocopolymer 1 (see Sec. III for further explanation).
Integral decay kinetics of phosphorescence from PtOEP and upconverted delayed fluorescence (DF) from spirocopolymer 1 at zero electric field (open characters) and at an electric field of (solid characters) at room temperature. The concentration of PtOEP was 1 wt % and excitation was performed at 537 nm (2.31 eV). A gate window of 10 ms was chosen for the detection.
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