Photoconversion of 6,13-α-diketopentacene single crystals exhibiting light intensity-dependent morphological change

Recently, we revealed that 6,13-dihydro-6,13-ethanopentacene-15,16-dione (PDK) could be quantitatively photoconverted into pentacene even in the crystal phase, accompanied by the destruction of the crystals. In this work, we investigated the relationship between the photoinduced morphological changes and the light intensity for the photoconversion at a single micrometre-sized crystal level. Photoirradiation with a strong intensity (over 100 kW cm-2) resulted in hole formation in a single crystal. When medium intensity (0.5-100 kW cm-2) was irradiated, destruction including separation and jumping of the crystal was observed. Absorption spectrum measurement of the single crystal revealed that when almost same number of pentacene was generated, the destruction was induced by the generated strain within crystal due to the stacking mismatch between the different molecules. Upon photoirradiation with a low intensity (below 0.5 kW cm-2), protruding pillar objects were observed on the crystal surface. This formation is a result of the surface movement of molecules through the relaxation of strain. Our results provide important insight into stimuli-responsive crystal materials and could contribute to the generation and application of remotely controllable smart materials.