Wavelength tunable ultralong room temperature phosphorescence from 3D-printable benzoindole based materials

Organic ultralong room temperature phosphorescence (URTP) materials have attracted growing interest due to their persistent afterglow and potential applications in information security, anti-counterfeiting, and advanced photonic systems. Herein, a series of benzoindole (Bd)-based emitters with progressively extended π-conjugation (Bd-NH₂, Bd-NAP, Bd-PHE, and Bd-PYR) were rationally designed and synthesized to elucidate the effect of π-extension on triplet-state regulation and phosphorescence behavior. Photophysical investigations reveal that all Bd derivatives exhibit characteristic π-π* transitions and efficient triplet emission at low temperature, with emission maxima gradually redshifting as the conjugation length increases. When incorporated into a poly(lactic acid) (PLA) matrix, the resulting Bd@PLA composite films display photo-activated room-temperature phosphorescence with lifetimes extending from hundreds of milliseconds to the second regime. The rigid and oxygen-barrier microenvironment provided by PLA effectively stabilizes triplet excitons and suppresses nonradiative decay. Time-dependent density functional theory (TD-DFT) calculations indicate that π-conjugation extension induces systematic evolution of frontier molecular orbital energy levels and spatial distributions, rationalizing the observed emission redshift and supporting the feasibility of triplet-state formation and stabilization. Benefiting from the excellent processability of PLA, the composites were successfully applied to two-dimensional patterns and three-dimensional printed structures, enabling spatially and temporally programmable luminescent outputs. This work provides a general strategy for constructing wavelength-tunable organic URTP materials through synergistic molecular design and polymer confinement.