Optical, thermal and mechanical activation of spiropyrans enhanced by hydrogen bonding interactions and its application in time–resolved encryption

Here, a multi–stimuli–responsive spiropyran molecule with enhanced photochromic, thermochromic and mechanochromic properties was constructed by introducing hydrogen bonding interactions, which is highly sensitive to external stimuli, and its solution and powder change color after two seconds of ultraviolet irradiation. After short–term grinding (10 min) or heating (90 ℃ for 3 min), the powder can also show rapid and reversible fluorescence emission change. The molecule can withstand at least 5 reversible grinding–recrystallization cycles, 5 heating–white light cycles or 20 reversible UV– white light cycles. To our best knowledge, it is seldom reported that spiropyran compounds achieve multi–stimuli response by introducing hydrogen bonds, and there are also rare reports on the influence of hydrogen bonds on multi–stimuli performance. Hydrogen bond interaction makes the spiropyran molecule more sensitive to external stimuli to achieve the multi–stimulus response. Combined with this good photochromism, mechanochromism and thermochromism, a time–resolved multilevel information encryption was explored, which has the following advantages: (1) According to the actual demand, designing and adding the combination of numbers or letters can encrypt a lot of information. (2) The process involves three kinds of stimuli responses (photochromism, mechanochromism and thermochromism), and the complex information switching ensures that the real information is not easy to leak. (3) The encryption and decryption steps are easy to operate and can lower the application threshold. This work is a rare example of improving the photochromism, mechanism and thermochromism of spiropyrans by hydrogen bonding, which can also provide guidance for designing functional spiropyrans for multi–level information encryption.