Phosphorescent carbon dots (CDs) capable of excitation-dependent excitation and stable emission in aqueous environments remain fundamentally challenging due to inefficient intersystem crossing and rapid triplet deactivation. Herein, we report a confinement-enabled strategy to regulate excited-state dynamics by integrating malic acid/ethylenediamine-derived CDs within a CaSiO3 matrix (MA/EA-CDs@CaSiO3) via a one-pot in situ formation strategy. We show that the rigid inorganic framework, together with Ca2+-induced local electric fields, synergistically suppresses nonradiative relaxation and facilitates intersystem crossing, leading to efficient stabilization of triplet excitons. As a result, the composites exhibit pronounced visible-light-excitable phosphorescence with quantum yields up to 23.78% in the solid state and ∼10% under 395 nm excitation. Notably, the confined structure preserves long-lived emission even in aqueous environments, indicating effective protection of triplet states against oxygen and solvent-induced quenching. Beyond performance, this work elucidates how inorganic confinement and local coordination environments cooperatively regulate excited-state processes in carbon-based luminophores. The design strategy established in this work provides a generalizable framework for constructing aqueous-compatible phosphorescent systems and advancing the fundamental understanding of room-temperature phosphorescence in hybrid materials.
A conjugated molecular sensing platform is presented that integrates selective Hg2+ recognition with visible colorimetric response, charge-transfer photophysics, photocurrent modulation, and smartphone-assisted digital readout within a single system. The sensor is based on an oligo(p-phenylenevinylene) (OPV) backbone bearing terminal benzimidazole units, designed to couple intramolecular charge transfer (ICT) with coordination-driven supramolecular organization. Density functional theory (B3LYP/6-31G*) revealed a partially nonplanar geometry with asymmetric frontier orbital distribution. Hg2+ binding in THF induced a pronounced bathochromic shift (∼25 nm) and a ratiometric fluorescence response with a detection limit of 5.6 ppb, while maintaining excellent selectivity over competing ions. A 1:1 binding stoichiometry was established with an association constant of K = 1.81 × 104 M−1, and spectroscopic analyses confirmed metal-assisted aggregation and conformational rigidification as key amplification mechanisms. Notably, the probe also functioned as an active photodetector layer, exhibiting reproducible, wavelength-dependent photocurrent switching under blue (450 nm), green (555 nm), and red (650 nm) illumination at −1 V bias. The pristine device displayed maximum photosensitivity (∼180%) and highest responsivity under red excitation, while Hg2+ coordination induced a ∼9.8-fold suppression in red-light photocurrent along with significant modulation of responsivity, detectivity (D*), and external quantum efficiency (EQE), consistent with ICT-state stabilization and trap-assisted recombination. Further, the sensing response was translated onto a paper substrate for reversible, naked-eye detection and quantitative smartphone-based RGB analysis (R2 > 0.99). This unified optical–electronic–digital approach offers a robust, field-adaptable framework for monitoring toxic heavy metal pollutants.
