Ultralong room-temperature phosphorescence of a solid-state supramolecule between phenylmethylpyridinium and cucurbit[6]uril

Abstract

Long-lived organic room-temperature phosphorescence (RTP) has received great attention because of its various potential applications. Herein, we report a persistent RTP of a solid-state supramolecule between a cucurbit[6]uril (CB[6]) host and a heavy-atom-free phenylmethylpyridinium guest. Significantly, the long-lived phosphorescence completely depends on the host-guest complexation, revealing that the non-phosphorescent guest exhibits a 2.62 s ultralong lifetime after being complexed by CB[6] under ambient conditions. The ultralong RTP is because of tight encapsulation of CB[6], which boosts intersystem crossing, suppresses nonradiative relaxation and possibly shields quenchers. Moreover, several phosphorescent complexes possessing different lifetimes are prepared and successfully applied in triple lifetime-encoding for data encryption and anti-counterfeiting. This strategy provides a new insight for realizing purely organic RTP with ultralong lifetime and expands its application in the field of information protection.

Scheme 1. Schematic illustration of the solid-state supramolecular strategy and Jablonski diagram for radiative and non-radiative processes. (KFluor is the radiative rate constant of the lowest excited singlet state S₁; KFluonr is the nonradiative rate constant of the lowest excited singlet S₁; K_isc is the intersystem crossing rate constant from the excited singlet state to the triplet state; KPhosr is the radiative rate constant of the lowest excited triplet state T₁; KPhosnr is the nonradiative rate constant of the lowest excited triplet state T₁; τ_Phos is the lifetime of the excited triplet state; Φ_Phos is the quantum yield of phosphorescence; and Φ_isc is the quantum yield of intersystem crossing from the excited singlet state to the triplet state; inset: the molecular structures of the guests and host).

Fig. 1. Photophysical properties of PX/CB[6]. (a) Excitation (black), photoluminescence (magenta) and phosphorescence spectra (olive) of PBC/CB[6] in the solid state; (b) time resolved PL decay of PBC/CB[6] at 510 nm in the solid state at room temperature; (c) luminescence photographs of PBC/CB[6] and PCC/CB[6] powder under 365 nm UV irradiation and at different time intervals after removal of the ultraviolet lamp.

Fig. 2. (a) ¹H NMR spectra of PBC/CB[6] and PBC; (b) high resolution mass spectrometry of PBC/CB[6]; (c) XRD patterns of PBC/CB[6] (wine) and PYCl/CB[6] (black); (d) phosphorescence quantum yield (Φ_p) and lifetime (τ) of PX/CB[6].

Fig. 3. Schematic illustration of lifetime-encoding for security applications using PYCl/CB[6], PCC/CB[6] and PBC/CB[6].