Julolidine‐Functionalized Amphiphilic Aza‐BODIPY Dyes: Synthesis, Near‐Infraed‐II Emission, and pH‐Response

A series of amphiphilic aza‐BODIPY dyes ( 1a‐d ) bearing two julolidine units at 1,7‐positions of the azadipyrromethene core and hydrophilic oligo(ethylene glycol) chains at the 3,5‐phenyls were synthesized and characterized. All dyes feature broad, panchromatic absorption bands from 350 nm up to 1000–1100 nm in CH 2 Cl 2 and exhibit near‐infrared (NIR‐II) emission bands up to 1400 nm. Solvent‐dependent absorption and fluorescence spectroscopic studies reveal pronounced positive solvatochromism of these dyes and further Lippert–Mataga analyses reveal their efficient intramolecular charge transfer character. The optical properties of these dyes are strongly influenced by the substitution patterns as well as the linker structures (–OCH 2 – or –N(CH 2 ) 2 ) for the hydrophilic moieties at the 3,5‐phenyls, which is further elucidated by density functional theory calculations. Notably, dye 1b exhibits the most red‐shifted emission (1109 nm in DMSO) with a high fluorescence quantum yield (2.0%). In addition, all dyes display reversible spectroscopic pH‐response. These results underscore the promising application potential of these new aza‐BODIPY dyes.