Multicolor Fluorescence Writing Based on Host–Guest Interactions and Force‐Induced Fluorescence‐Color Memory

Abstract

An ew strategy is reported for multicolor fluorescence writing on thin solid films with mechanical forces.T his concept is illustrated by the use of ag reen-fluorescent pentiptycene derivative 1,w hichf orms variably colored fluorescent exciplexes:achange from yellow to red was observed with anilines,a nd fluorescence quenching( ac hange to black) occurred in the presence of benzoquinone.M echanical forces,s uch as grinding and shearing,i nduced ac rystalline-to-amorphous phase transition in both the pristine and guest-adsorbed solids that led to ac hange in the fluorescence color (mechanofluorochromism) and am emory of the resulting color.F luorescence drawings of five or more colors were created on glass or paper and could be readily erased by exposure to air and dichloromethane fumes.The structural and mechanistic aspects of the observations are also discussed.Smart materials undergo reversible changes in their properties in response to external stimuli. An ew type of smart materials that display mechano-, vapo-, and/or thermofluorochromism in the solid or liquid-crystalline phase has recently emerged:T heir fluorescence color and intensity are altered by mechanical forces,such as grinding,pressing,and shearing, but the initial state can be recovered by annealing and/or exposure to vapors of organic compounds or even water. [1,2] Themechanofluorochromic (MFC) behavior has been attributed to force-induced changes in intermolecular interactions as ar esult of either a( liquid-)crystalline-to-(liquid-)crystalline or crystalline-to-amorphous phase transition. As compared to dichromic MFC systems,t he multicolor counterparts [3][4][5] have enhanced color contrast and patterning,w hich is beneficial for applications in sensors,d isplays,s ecurity printing, and data-storage devices.H owever,M FC systems that enable multicolor fluorescence writing or drawing as well as switching are rare;p revious examples based on polymorphic [4] or bichromophoric [5] systems display up to three colors but require the careful control of temperature or mechanical forces.W er eport herein an ew strategy toward multicolor fluorescence writing,i nw hich as ingle chromophore is sufficient and the fluorescence color tuning is performed by guest molecules through host-guest interactions and exciplex formation at ambient temperature.T his approach is demonstrated with the pentiptycene-derived9,10-bis(phenylethynyl)anthracene 1 by the drawing of an apple, an orange,and abanana on athin film of 1 on glass or paper (Figure 1; see also Figures S1-S3 in the Supporting Information). Thei mportant role of the pentiptycene scaffold in the observed multicolor fluorescence writing is evidenced by comparison with the pentiptycene-free planar analogue 2.Thedesign of 1 as aguest-responsive MFC material relies on the prevention of compact intermolecular p stacking of the p-conjugated systems by the rigid bulky H-shaped pentiptycene scaffold [6] in the solid state,sothat aggregation-induced fluorescence quenching is minimized and pore volumes ac...

Easily Prepared and Reusable Films for Fast-Response Rewritable Light Printing

“…Color-changing technologies responding to light, − temperature, − water, − and force − have provided new strategies to design paper with rewritable ability. ,− Photochromism, as a promising technology, could be used to design and fabricate rewritable paper. Now, many photochromic materials have been prepared by incorporating organic dyes (typically, spiropyran − or diarylethene − ) into conventional paper.…”