3,5‐Dicyanopyridine–Phenothiazine Derivatives Exhibiting Single‐Molecular White Emission for Down‐Converting Electroluminescent Devices

ABSTRACT 3,5‐Dicyanopyridine and phenothiazine derivatives exhibit attractive mechanochromic properties that enable multicolour emissions and single‐molecular white emission. Large hypsochromic shifts of up to 190 nm (from red to deep blue) were observed in the developed mechanochromic compounds in response to various external stimuli. These derivatives exhibit record‐breaking solid‐state emission enhancement factors of up to 755, indicating that the emission intensity of their solids is substantially higher than that of solutions. Single‐molecular white light emitting samples were obtained by the tuning of the substituent nature in the pyridine ring and physical approaches (different treatments of aggregate‐containing liquids and solid samples). The developed compounds possess different conformational states, with emissions ranging from deep blue to red. The amorphous states exhibit single‐colour emissions, while crystalline states of various packing arrangements show white or multicoloured emissions. They can be used as down‐conversion white emitters in white light‐emitting diodes exhibiting colour coordinates of (0.32, 0.34), (0.28, 0.30) and (0.32, 0.38), colour rendering index (CRI) of 75–78 and colour temperatures in the range from 5368 to 6668 K.