Highly efficient halochromic behaviors in solution and film states with 9,19-dichloro-5,15-dihydrocarbazolo[3′,4':5,6][1,4]oxazino[2,3-b]indolo[3,2-h]phenoxazine derivative

We demonstrated 9,19-dichloro-5,15-bis(2-decyltetradecyl)-5,15-dihydrocarbazolo[3′,4':5,6][1,4]oxazino [2,3-b]indolo [3,2-h]phenoxazine (DTD-CzDxz) as a new halochromic compound with a prominent UV–vis absorption spectral response under acidic conditions. DTD-CzDxz was constructed with branched alkyl chains at the ends of a planar fused molecule to achieve good solubility in common organic solvents. When the nitrogen in the oxazine ring was diprotonated, the entire absorption spectrum shifted from the visible region to the near-infrared (NIR) region for both solution and film states. Owing to a significant red shift of 256 nm in the solution state, the color of the sample quickly faded and the sample became colorless and transparent and could be easily recognized by the naked eye. In addition, the photoluminescence spectrum of DTD-CzDxz displayed significantly weakened emission intensity at 650 nm under acidic condition. When triethylamine was added into the acid-treated solution, the emission intensity at 650 nm was restored to its initial value. The neat DTD-CzDxz film was transparent and colorless film when exposed to acid vapors. However, the absorption spectrum reverted to its original form as soon as the film was exposed to air at room temperature. The efficient cyclizability due to the halochromism of the DTD-CzDxz film showed that there was no significant degradation in the absorption intensity at 567 and 794 nm. Hence, it could be concluded that DTD-CzDxz is a good candidate for solid-state halochromic sensors that can operate under both acidic and basic conditions.