Temperature dynamics reflect the physiological state of cells, and accurate measurement of intracellular temperature helps to understand the biological processes. Herein, we report a novel nanothermometer by conjugating a fluorescent probe 3-ethyl-2-[4-(1,2,2-triphenylvinyl)styryl]benzothiazol-3-ium iodide (TPEBT) with a thermoresponsive polymer poly(N-isopropylacrylamide-co-tetrabutylphosphonium styrenesulfonate) [P-(NIPAM-co-TPSS)]. The derived nanoprobe TPEBT-P(NIPAM-co-TPSS) self-assembles into micelles with TPEBT as hydrophobic core and PNIPAM as hydrophilic shell. It exhibits aggregation-induced emission (AIE) at λ ex /λ em = 420/640 nm in aqueous medium with a quantum yield of Φ F 11.9%. The rise in temperature transforms PNIPAM chains from linear to compact spheres to serve as the core of micelles, and meanwhile converts TPEBT from the state of aggregation to dispersion and redistributes in the micellar shell. Temperaturedriven phase transition of P(NIPAM-co-TPSS) mediates the reversible aggregation and disaggregation of TPEBT and endows the nanothermometer with temperature-dependent AIE features and favorable sensitivity for temperature sensing in 32−40 °C. TPEBT-P(NIPAM-co-TPSS) is taken up by HeLa cells to distribute mainly in lysosomes. It enables quantitative visualization of in situ thermal dynamics in response to stimuli from carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, oligomycin, genipin, and lipopolysaccharide. The real-time monitoring of photothermalinduced intracellular temperature variation is further conducted.

The thermo-responsive and fluorescent nature of a poly­(ionic liquid) (PIL) is tailored by reversible addition-fragmentation transfer (RAFT) copolymerization of 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) and ionic liquid tetrabutylphosphonium styrenesulfonate ([P4444]­[SS]). The PIL is shortly termed as poly­([P4444]­[SS]-DDMAT). In this strategy, DDMAT plays the following multiple functions: (1) it serves as an RAFT reagent to ensure precise control of the molecular weight of PIL; (2) its dodecyl chain is grafted at the chain end of PIL to reduce the cloud point temperature (T cp); and (3) it regulates the fluorescence properties of PIL to induce a redshift of the emission. The T cp of PIL decreases with the increment of its molecular weight and concentration, while it increases with the enhancement in pH and salt level. PIL displays blue-green fluorescence (λex/λem = 392/478 nm) in an aqueous medium with a quantum yield (Φ) of 0.86% and a lifetime (τ) of 1.09 ns. It also shows thermo-responsive fluorescence activity. Its phase transition temperature from clear to turbid is tailored into a range covering the physiological temperature. The variation of temperature within a certain range is made to be visually visible based on the degree of turbidity, which well ensures skin surface temperature sensing and facilitates preliminary diagnosis of fever.