Reversible Change in Fluorescent Color of Moisture‐sensitive Binary Films of 4‐[Bis(4‐methylphenyl)amino]benzylideneaniline with Organic Acids

Abstract

Novel moisture‐sensitive binary films that exhibit reversible change in fluorescent color have been created using a fluorescent amorphous molecular material, 4‐[bis(4‐methylphenyl)amino]benzylideneaniline (BMBZA), with organic acids such as pentafluorobenzoic acid and benzoic acid. Orange fluorescent color of the film under ambient dry atmosphere was found to change drastically to greenish blue under wet atmosphere. Response speed of such color change was quite fast and it responded well to exhaled breath. It was suggested that such change in fluorescent color was due to switching the excited species between BMBZA and its protonated iminium cation, and that the acidity level of the organic acids was an important factor for exhibiting such reversible changes in fluorescent colors. In addition, excited‐state intermolecular proton transfer was suggested to contribute the orange fluorescence under dry atmosphere.

Emission Properties of Hybrid Films of Benzylideneaniline-based Amorphous Molecular Materials with Organic Acids

“…1 shows electronic absorption and fluorescence spectra of single BFBZA film. Electronic absorption band with a λmax of 370 nm with a shoulder around 400 nm was observed, being in the similar wavelength region to the single BMBZA film [23]. With regard to fluorescence spectrum, the emission band of BFBZA film with a λmax of ca.…”

“…With regard to fluorescence spectrum, the emission band of BFBZA film with a λmax of ca. 500 nm was somewhat red-shifted relative to that of BMBZA film [23]. The result might be due to the fact that the π-conjugation system was more extended by introduction of fluorenyl groups.…”

“…The result might be due to the fact that the π-conjugation system was more extended by introduction of fluorenyl groups. As well as BMBZA-BA and BMBZA-PFBA films [23], a novel hybrid film of BFBZA-BA was found to exhibit reversible change in emission color in response to exhaled breath. The film emitted orange in color upon irradiation with UV lamp (365 nm) under ambient dry atmosphere.…”

“…For example, we have reported that spincoated films of diarylaminobenzaldehyde-based emitting amorphous molecular materials exhibited vapochromic emission [11]. In addition to such materials with single component systems, we have recently been studying the creation of hybrid systems of amorphous molecular materials with other materials exhibiting smart functions [13][14][15][16][17][18][19][20][21][22][23]. We have reported that the hybrid films of aminoazobenzene-based amorphous molecular materials with organic acids exhibited drastic and reversible color changes in response to moisture [20].…”

“…Novel moisture-sensitive hybrid films composed of diarylaminobenzaldehyde-based emitting amorphous molecular materials with ptoluenesulfonic acid were found to exhibit OFF-ON switching of fluorescent in response to moisture [22]. Very recently, we have investigated the response of emission properties to moisture for hybrid films composed of 4-[bis(4-methylphenyl)amino]benzylideneaniline (BMBZA) with a variety of organic acids, and finally found that hybrid films of BMBZA with organic acids with appropriate acidities, benzoic acid (BA) and pentafluorobenzoic acid (PFBA), exhibited the emission color changes in response to moisture [23].…”