Photoinduced Surface Relief Grating Formation Using Mixed Amorphous Films of Molecular Materials: 4-[4'-Stearoyloxybiphenyl-4-yl(biphenyl-4-yl)-amino]azobenzene-4,4',4''-Tris[3-methylphenyl-(phenyl)amino]triphenylamine System

Abstract

photoinduced SRG formation using a mixed film of DBAB-St and m-MTDATA has been investigated. ExperimentalDBAB-St was synthesized as follows: stearoyl chloride (0.70 g, 2.3 mmol) was added to a THF solution (20 mL) of 4-[4'-hydroxybiphenyl-4-yl(biphenyl-4-yl)amino]azobenzene (DBAB-OH: 1.0 g, 1.9 mmol), prepared by the procedure reported in our previous paper [ 23 ], and triethylamine (0.39 g, 3.9 mmol), and then the solution was stirred for 2 h at room temperature. After the solvent was removed under reduced pressure, the product was purified by silica-gel column chromatography using toluene as an eluent, followed by recrystallization from ethanol. Yield: 0.78 g (52%), m. Differential scanning calorimetry (DSC) was carried out by means of DSC6220 (Seiko Instruments Inc.) Photoinduced SRG formation was carried out by using a compact CW laser (488 nm: CYAN-488-100NH-W, Spectra Physics) as a source of writing beams. Atomic force microscopy (AFM) was performed by means of Scanning Probe Microscope (JSTM-4200D, JEOL Ltd.) with a micro cantilever (OMCL-AC160T-C2, Olympus). Results and discussionA novel photochromic amorphous molecular material, DBAB-St, was synthesized by the reaction of DBAB-OH with stearoyl chloride in the presence of triethylamine and identified by various spectroscopy and mass spectrometry (Scheme 1). DBAB-St was found to readily form an amorphous glass when the melt sample was cooled on standing in air.The Tg was determined to be 19 °C by DSC, which was considerably lower than that of the parent material, 4-[di(biphenyl-4-yl)amino]azobenzene (68 °C) [24]. The existence of the flexible long alkyl chain is assumed to reduce the Tg. The Tg of DBAB-St was found to be increased by mixing with m-MTDATA; the Tg of the mixed glass of DBAB-St and m-MTDATA with a ratio of 1:4 (w/w) was determined to be 48 °C.Using the amorphous films of DBAB-St and the mixed film of DBAB-St and m-MTDATA with a ratio of 1:4 (w/w), photoinduced SRG formation was investigated. The amorphous films were irradiated with two writing beams (488 nm) with incident angles of +10° and -10° with respect to the normal of the sample film and with polarization angles of +45° and -45° with respect to the p-polarization at 3 mW (ca. 95 mWcm -2 ) each (Fig. 1). J. Photopolym. Sci. Technol., Vol. 24, No. 5, 2011 528 Fig . 2 shows the growth of diffraction efficiency upon irradiation with writing beams at 20 °C.Whereas significant increase in diffraction efficiency could not be observed for the DBAB-St amorphous film upon irradiation with the writing beams, the diffraction efficiency gradually increased and reached to ca. 7% in 30 min for the mixed film of DBAB-St and m-MTDATA. In addition, SRG with a modulation depth of 170-190 nm was confirmed to be inscribed on the mixed amorphous film by means of AFM as shown in Fig. 3. Thus, the mixing with m-MTDATA drastically enhanced the SRGforming ability of DBAB-St.As discussed in our previous paper [13], the increasing Tg of the material prevents the collapse of the SRG due to surface tension to...

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“…The inscription of SRG has also been explored on amorphous low-molecular-weight molecular materials. ,,,− Nakano et al compared the gratings formation between several amorphous films composed of azotriarylamine derivatives (Figure u–x), and Ishow et al performed a comparative study of several molecular glasses . There are in addition several examples where the authors proved that their material was in a crystalline phase. ,− Nakano et al, for instance, observed the formation of SRG at the surface of a single crystal of 4-(dimethylamino)­azobenzene (Figure y).…”