C10910 01

All solvents were used as purchased from the Tokyo Chemical Industry (Tokyo, Japan) or Fuji Film-Wako Chemicals (Tokyo, Japan). All synthesis procedures for BN1-4 were provided in the previous report (Ando et al., 2019 (link)). Absorption spectra of the samples were measured using an ultraviolet–visible,-near-infrared spectrometer (Lambda 950-PKA, Perkin-Elmer, MA, United States). Fluorescence and phosphorescence spectra were measured using a spectrofluorometer (FP-8600, JASCO International, Japan). The photoluminescence quantum yield (PLQY) was measured using a PLQY measurement system (Quantaurus-QY, Hamamatsu Photonics, Hamamatsu, Japan). The transient PL decay characteristics of BN4 in toluene were recorded by a dynamic range streak camera system (C10910-01, Hamamatsu Photonics, Hamamatsu, Japan) with a third harmonic YAG laser (355 nm, 10 Hz, PL-2250, EKSPLA, Lithuania) as an excitation source. The transient PL emission and PL decay of BN1, 2, 3, and 4 doped in a DPEPO host film were recorded under vacuum with a streak camera (C4334, Hamamatsu Photonics, Hamamatsu, Japan) with a third harmonic YAG laser (266 nm, 10 Hz, LS-2132UTF, LOTIS TII, Belarus) as an excitation source.

A spectrophotometer (LAMBDA 950-PKA, PerkinElmer) is used to measure the ground-state ultraviolet-visible (UV-vis) absorption spectra. The steady-state fluorescence at room temperature and phosphorescence at the low temperature (77 K) are recorded by spectrofluorometer (JASCO FP-8600). PLQYs are evaluated by Hamamatsu Photonics C11347-01 Quantaurus-QY. To prevent the interruption from the ambient moisture and oxygen, a 15-min nitrogen-gas bubbling is conducted for the dyes in solution, while the measurement of solid-state films is performed under argon-gas flow. Time-resolved transient photoluminescent (PL) decay profiles are recorded using a Quantaurus-Tau system (C11367-03, Hamamatsu Photonics, Japan) and a time-resolved spectroscopy setup, composed of a third harmonic wave generation, a Nd:YAG/YVO lasing source (EKSPLA PL-2250, the excitation wavelength of 355 nm, and a pulse width of 30 ps), and a streak camera (C10910-01, Hamamatsu Photonics).