Fig.1 （A） UV-Vis absorption spectra and （B） fluorescent emission spectra of AM-RhB in THF with different molar of hydrochloric acid （n（AM-RhB）=0.3 mmoL，V（AM-RhB）=3 mL， λex = 530 nm， slit width： 3 nm， 3 nm）； （C） Structural changes of molecules in solution

Fig.2 Schematic diagram of hydrochromic fluorescent materials based on the principle of “over-protonation”

Fig.3 （A） Schematic diagram of the material structure； （B） The UV-Vis reflective spectra and （C） fluorescence emission spectra of the “off-on” mode material before and after adding water （λex=560 nm， slit width： 5 nm， 3 nm）； （D） Plot of visible reflection（left） and fluorescent emission intensity（right） at λmax of hydrochromic fluorescent materials based on different acid （λex = 560 nm， slit width： 5 nm，3 nm）；（E） Picture of materials in different condition

Fig.4 （A） The UV-Vis reflective spectra and （B） fluorescence emission spectra of the “on-off” mode material before and after adding water （λex = 550 nm， slit width： 5 nm， 3 nm）； The change of （C） color and （D，E） visible reflection of SFA， MO and mixture before and after adding water

Fig.5 （A） Time-dependent reflectivity variations at 568 nm for AM-RhB based WJRP upon adding a droplet of water during 0~500 s， respectively. Blue arrows indicate the moment of adding water. （B） L*， a*， b* measured by spectrodensitometer and photographs of the “off-on” mode paper before （up） and after （down） adding water， respectively. （C） Microscopic images （up） and fluorescence images （down） of the “off-on” mode paper before and after addition of water

Fig.6 （A） Photographs during 5 consecutive print-erase rounds on the dual-mode hydrochromic paper. （B） A plot of the reflectivity at 568 nm and （C） fluorescent intensity at 592 nm versus the number of cycles as the WJRP is cycled through water spraying （Write） and water removal （Erase） by means of wetting/heating at 60 ℃ （λex = 560 nm， slit width： 5 nm， 3 nm）