Fig. 2

Luminescent properties of the host molecules. a Steady-state photoluminescence (PL) spectrum, delayed PL spectrum (λ_ex = 254 nm) and mechanoluminescence (ML) spectrum of PCP crystals at ambient conditions. Insert: photos of PCP crystals under 254 nm UV light irradiation and after the UV irradiation ceased under ambient conditions (left); photos of ML produced by crushing PCP crystals on the wall of a glass vial under soft room lighting and in the dark respectively (right). b Steady-state PL spectrum (λ_ex = 254 nm) and ML spectrum of PA crystals at ambient conditions. Insert: photos of PA crystals under 254 nm UV light irradiation and after the UV irradiation ceased (left); photos of PA crystals being crushed on the wall of a glass vial under soft room lighting and in the dark respectively (right). c Steady-state PL spectrum, delayed PL spectrum (λ_ex = 254 nm) and ML spectrum of DCB crystals at ambient conditions. Insert: photos of DCB crystals under 254 nm UV light irradiation and after the UV irradiation ceased (left); photos of ML produced by crushing DCB crystals on the wall of a glass vial under soft room lighting and in the dark respectively (right). For delayed spectra in (a) and (c), delay time (Δt) = 50 ms. d Time-resolved PL decay curves of PCP crystals at 510 nm and DCB crystals at 550 nm (λ_ex = 254 nm). Insert: time-resolved PL decay curves of PCP crystals at 350 nm, PA crystals at 342 nm and DCB crystals at 335 nm (λ_ex = 280 nm). ϕ_{(F + P)}: overall quantum yield; τ_F: fluorescence lifetime; τ_P: phosphorescence lifetime