Reversible three-state switching of multicolor fluorescence emission by multiple stimuli modulated FRET processes within thermoresponsive polymeric micelles.

Experimental Section Materials. N-Isopropylacrylamide (NIPAM, 97%, Tokyo Kasei Kagyo Co.) was purified by recrystallization from a mixture of benzene and n-hexane (1/3, v/v). Styrene (St, 99.5%, Beijing Chemical Factory) was successively washed with aqueous NaOH (5.0 wt %) and water, then distilled over CaH 2 at reduced pressure. 4-Chloro-7-nitrobenzofurazan (NBD-Cl, 99%), 2,3,3-trimethylindolenine (98%), and 5-nitrosalicylaldehyde (98%) were purchased from Alfa and used as received. 2,2-Azoisobutyronitrile (AIBN) was recrystallized from 95% ethanol. Rhodamine B (RhB, Acros), hydrazine hydrate, and all other reagents (Sinopharm Chemical Reagent Co.) were used as received. Acryloyl chloride (Sinopharm Chemical Reagent Co.) was distilled prior to use. Dichloromethane (CH 2 Cl 2) and acetonitrile (MeCN) were dried over CaH 2 and distilled just prior to use. Water was deionized with a Milli-Q SP reagent water system (Millipore) to a specific resistivity of 18.4 MΩcm. S-1-propyl