Acid–base vapor induced reversible morphological transformation of organic microcrystals: revealing photophysical “on/off” switches

• New organic microcrystals were facilely prepared.
• Reversible morphological transformation stimulated by acid–base vapors.
• Photophysical “on/off” switches controlled by morphology.
• Hexangular microflake morphology serves as NIR and mid-IR absorption switches.

In the present work, the morphology of organic microcrystals can be reversibly transformed between three-dimensional microprism and two-dimensional hexangular microflake by external acid–base vapor stimuli, which is accompanied by the reversible phosphorescent color and near-infrared (NIR) absorption intensity transformation. Other unusual features are that the fumigation of such microcrystals with HCl–NH3 vapors exhibits NIR and middle-infrared (mid-IR) absorption “on/off” switches. Thus, interesting NIR absorption (at 1950 nm) and mid-IR absorption (at 3728, 3892 and 4005 nm) “on/off” switches have been first realized by using the present organic microcrystal materials which might have a significant effect on the design strategy of molecular device and switch. Present work will provide new organic microcrystals for promising candidates for applications in NIR and mid-IR absorption switch materials.