Tuned Intra- and Intermolecular Photoreactions of Tridentate Cyanostilbenes with Distinct Aggregated-State Photomechanical and Dispersed-State Photochromic Behaviors

Developing a new strategy to realize on-demand photoreactions with distinguishable signals is highly desirable. Herein, by simply tuning the molecular state, tuned photoreactions with different dynamic signals based on a series of tridentate cyanostilbene molecules (TCS1-5) are realized. The results show that in the crystalline state, the ordered and densely molecular packing facilitates the successive intermolecular photocycloaddition between adjacent cyanostilbene molecules and causes accumulated stresses within the crystals, which further induces variable photo-induced mechanical motions such as peeling, bending, twisting, and so on. In the monodispersed solution state, however, the larger distances between TCS1-5 molecules afford a photo-induced radical-assisted intramolecular photocyclization process and give rise to multiple domino photochromic and photofluorochromic behaviors. Based on their distinct yet controllable thermostability and radical colors, photochromic films are fabricated from TCS1@PMMA and TCS1/TFA@PMMA for Morse code and rewritable photopatterning applications, showing excellent photochromism. By coating TCS3 on a piece of plastic bag, the macroscopic mechanical motion is achieved by amplifying the collective molecular motion from the nanoscale up to the macroscopic dimension. The molecular state-based strategy reveals the regularity between photoreactions and molecular packing and further provides an opportunity to rapidly access controllable photoresponsive systems.