Narrowband Organic Afterglow Materials Exhibiting 11.2 nm FWHM, 38% Phosphorescence Efficiency and 1.5 s Emission Lifetime Under Ambient Conditions.

Narrowband organic room-temperature phosphorescence (RTP) remains rare due to significant high-frequency vibronic coupling in T1→S0 electronic transition, where T1 and S0 represent the lowest triplet excited state and ground state, respectively. Here, we report coronene-derived (CoDe) luminophores exhibiting ultra-narrowband RTP (full width at half maximum FWHM = 11.2 nm) with a 1.5 s lifetime and 38% afterglow efficiency in a phenyl benzoate (PhB) matrix. The narrow emission arises from enhanced coupling with low-frequency vibrational modes in localized excitation (LE) states, as supported by vibronic simulations. Under high-power excitation, the CoDe-PhB further exhibits organic long-persistent luminescence (OLPL) lasting over 40 min (FWHM = 14.7 nm), governed by a two-photon ionization-induced charge-separation mechanism. The materials are processable via melt-casting and excitable by ambient or white light, offering practical utility for high-color-purity afterglow display and lighting applications. This work establishes low-frequency vibronic engineering as a new route to narrowband RTP and OLPL emitters beyond conventional multi-resonance-based designs.