Luminescent materials are widely used for imaging and sensing owing to their high sensitivity, rapid response and facile detection by many optical technologies1. Typically materials must be chemically tailored to achieve intense, photostable fluorescence, oxygen-sensitive phosphorescence or dual emission for ratiometric sensing, often by blending two dyes in a matrix. Dual-emissive materials combining all of these features in one easily tunable molecular platform are desirable, but when fluorescence and phosphorescence originate from the same dye, it can be challenging to vary relative fluorescence/phosphorescence intensities for practical sensing applications. Heavy-atom substitution 2 alone increases phosphorescence by a given, not variable amount. Here, we report a strategy for modulating fluorescence/phosphorescence for a single-component, dual-emissive, iodide-substituted difluoroboron dibenzoylmethane-poly(lactic acid) (BF 2 dbm(I)PLA) solid-state sensor material. This is accomplished through systematic variation of the PLA chain length in controlled solvent-free lactide polymerization 3 combined with heavy-atom substitution2. We demonstrate the versatility of this approach by showing that films made from low-molecular-weight BF 2 dbm(I)PLA with weak fluorescence and strong phosphorescence are promising as 'turn on' sensors for aerodynamics applications 4 , and that nanoparticles fabricated from a higher-molecularweight polymer with balanced fluorescence and phosphorescence intensities serve as ratiometric tumour hypoxia imaging agents.Ratiometric sensing addresses challenges associated with sensor concentration and obviates the need for specialized luminescence lifetime instrumentation. For example, Kopelman and co-workers developed a powerful nanosensor (PEEBLEs) for ratiometric oxygen sensing comprising a cyanine dye standard and an O 2 -sensitive Pt porphyrin phosphor in a sol-gel matrix and demonstrated its utility for cell biology 5 . Single-component dye-polymer conjugates with both fluorescence and phosphorescence offer advantages over threecomponent dye/standard/matrix mixtures. Dual-emissive materials possess an internal rather than external standard in ratiometric sensing schemes, and thus, 1:1 fluorophore/phosphor stoichiometry, resulting in greater sample homogeneity and minimal dye leaching. Readily processable biomaterials combined with photostable, optically tunable dyes that emit brightly even in aqueous environments are beneficial for imaging and sensing in biomedical contexts. Previously, we discovered that difluoroboron dibenzoylmethane-poly(lactic acid) (BF 2 dbmPLA; as in Fig. 1, with hydrogen in place of iodide) exhibits unusual, long-lived green room-temperature phosphorescence (RTP) in addition to intense blue fluorescence 6 . Given that thermal decay pathways are often accessible, it is rare to see RTP from organic compounds; typically organized media7 , 8 or heavy atoms9 are required for RTP. This feature adds enhanced capability to the excellent fluorescence properties o...

Boron difluoride compounds are light emitting materials with impressive optical properties. Though their strong one- and two-photon absorption and intense fluorescence are well-known and exploited in molecular probes, lasers, and photosensitizers, phosphorescence, in contrast, is typically observed only at low temperatures. Here, we report that unusual room-temperature phosphorescence is achieved by combining a classic boron dye, difluoroboron dibenzoylmethane, BF2dbm, with poly(lactic acid) (PLA), a common biopolymer, resulting in a highly sensitive single-component oxygen sensor. Fluorescence quantum yields are enhanced, and temperature-sensitive delayed fluorescence is also observed. Multi-emissive BF2dbmPLA biomaterials show great promise as multifunctional molecular probes and sensors.

Difluoroboron avobenzone (BF(2)AVB), a simple boron complex of a commercial sunscreen product, exhibits morphology-dependent emission and mechanochromic luminescence in the solid state. When scratched, smeared, or even gently touched, the emission color of BF(2)AVB films is significantly red-shifted under UV excitation. In the rubbed regions, the fluorescence recovers slowly at room temperature or much faster with heating, resulting in a simple rewritable "scratch the surface" ink of potential commercial use.