Spin-coated films of squarylium dye J-aggregates exhibiting ultrafast optical responses

The formation of J-aggregates of squarylium dye derivatives in spin-coated films is reported. Squarylium dye derivatives with dipropylamino bases are found to spontaneously aggregate in a spin-coated film. Aggregation is prom oted when dye molecules are dispersed in a poly(vinyl alcohol) film, and wh en a spin-coated film of dye molecules is heated in the presence of acid va por. In particular: J-aggregates formed by exposure to acetic acid vapor sh ow the narrowest spectral width. J-aggregates formed by the acid treatment method are stable at room temperature and the spectral full-width at half m aximum of the J-band is 20 nm. Optical response of the acid-treated film is confirmed to exhibit a short relaxation time of bleached absorption of 300 fs.