Figure 2 Absorption, fluorescence, and phosphorescence spectra,
and photographs under natural light and UV light of (a) 5-TAT-OMe, (b)
6-TAT-OMe, (c) 5-TAT-H, (d) 6-TAT-H, (e) 5-TAT-CN, and (f) 6-TAT-CN in
bulk states and dichloromethane solutions.
the close molecular packing of π-planes. In addition, it is reported
that the host molecules could also provide a synergistic effect to the
guest at excited state via Förster resonance energy transfer (FRET) to
trigger the RTP behaviors of the guest.[13,27] The
host-guest hybrid films were fabricated by varying
luminogen:PPh3 molar ratio via a common melt-casting
method (Figure 1b and Figure S5), in which the blends of the guest and
host were heated to 85℃ under ambient conditions and then rapidly cooled
to reach crystalline states. As shown in Figure 3c, six melt-casting
host-guest films with 0.01mol% guests all exhibit obvious visible
afterglow after removal of 365 nm ultraviolet irradiation, implying the
presence of RTP. As shown in Figure 3d and Figure S2, a fluorescence
emission peak at 434 nm with a short lifetime of 4.15 ns, and a
phosphorescence emission peak at 520 nm with a long lifetime of 83.8 ms
are recorded in the photoluminescence spectra of pure
PPh3 crystalline films at room temperature. The
phosphorescence phenomenon of PPh3 can’t be captured by
naked eyes and the photoluminescence of PPh3 crystals is
weak with an overall quantum yield (ΦF+P) of 2.86%.
However, after doping the luminogens into PPh3, the
photoluminescence performance of the co-crystalline films is greatly
enhanced and the overall quantum yields are increased by 7 to 16 times
(Table 1). Especially, the RTP lifetime of host-guest hybrid films
elongated to the order of seconds (Figure 3e). Note that the
phosphorescence quantum yields (ΦP) of
6-TAT-OMe/PPh3, 6-TAT-H/PPh3, and
6-TAT-CN/PPh3 are 7.72%, 11.91%, and 29.35%,
respectively, which are higher than that of
5-TAT-OMe/PPh3 (7.31%), 5-TAT-H/PPh3(4.66%), and 5-TAT-CN/PPh3 (12.96%), respectively. The
enhancement of ΦP could be partially ascribed to the
increase in Kisc (Table 1). Among six host-guest
materials, 6-TAT-CN/PPh3 exhibits the largest
Kisc and Krp, thus
leading to the highest ΦP. Although the fast
Krp brings a slight decrease in the
phosphorescence lifetime of 6-TAT-CN/PPh3, it still
obtains a high value of 0.76 s (Figure 3e). These results are consistent
with the much brighter afterglow in 6-TAT-OMe/PPh3,
6-TAT-H/PPh3,