Fig. 1

Optical characterization of BPBBT. a Chemical structure of BPBBT. b Photographs and NIR-II fluorescence images of BPBBT (10 µM) in hexane (non-polar solvent), DMF (polar solvent) or THF containing 95% water (poor solvent for BPBBT) excited at 808 nm (100 mW cm⁻²). LE, locally excited state; TICT, twisted intramolecular charge transfer state; and AIE, aggregation-induced emission state. c Fluorescence emission spectra of BPBBT (10 µM) in different solvents after excitation at 831 nm. d Fluorescence emission spectra of BPBBT (10 µM) in hexane/THF mixture with hexane fraction from 0 to 100% excited at 831 nm. e Fluorescence emission spectra of BPBBT (10 µM) in water/THF mixture with water fraction from 0 to 95% excited at 831 nm. f Plot of I/I₀ of BPBBT versus water fraction in water/THF mixture. I and I₀ represent the fluorescence intensity of BPBBT (10 µM) in water/THF mixture with different water fraction and in THF, respectively. g Schematic illustration of the transformation of LE, TICT, and AIE states of BPBBT. D, donor; A, acceptor; IR, intramolecular rotation; RIR, restriction of intramolecular rotation; HOMO, Highest occupied molecular orbital; LUMO, Lowest unoccupied molecular orbital