Holographic recording and all-optical modulation in photochromic polymers

Linkage Isomerization via Geminate Cage or Bimolecular Mechanisms: Time-Resolved Investigations of an Organometallic Photochrome

The extent of the photoinitiated linkage isomerization of dicarbonyl(3-cyanomethylpyridine-κN)(η(5)-methylcyclopentadienyl)manganese (4) to dicarbonyl(3-cyano-κN-methylpyridine)(η(5)-methylcyclopentadienyl)manganese (5) was examined by time-resolved infrared spectroscopy on picosecond to microsecond time scales in room temperature isooctane to determine the extent the isomerization occurs as a geminate cage rearrangement. We previously reported that a substantial part of the conversion between 4 and 5 must be a bimolecular reaction between a solvent coordinated dicarbonyl(η(5)-methylcyclopentadienyl)manganese (3) and uncoordinated 3-cyanomethylpyridine. For the purpose of designing a molecular device, it would be desirable for the photoisomerization to occur in a geminate cage reaction, because the faster the isomerization, the less opportunity for side reactions to occur. In this study, assignments of transients are identified by comparison with transients observed for model reactions. Within 100 μs after photolysis of 4 in isooctane, no 5 is observed. Instead, the solvent coordinated 3 is observed within 25 ps after irradiation. The formation of 5 is observed only in the presence of 9 mM 3-cyanomethylpyridine but not until 10-50 μs after irradiation of 4. Within the limits of detection, these results indicate the conversion of 4 to 5 occurs exclusively via a bimolecular reaction of 3-cyanomethylpyridine with solvent coordinated 3 and not a geminate cage reaction between 3-cyanomethylpyridine and the dicarbonyl(η(5)-methylcyclopentadienyl)manganese fragment.

Biphotonic holographic grating recordings for different polarization configurations in spirooxazine-doped polymers

Spirooxazine-doped polymers exhibit a fast photochromism response and high polarization sensitivity after irradiation in the short-wavelength range. Based on such properties, holographic grating recordings accompanying a linearly polarized blue-violet beam (405 nm) in a photochromic film were performed by two coherent green beams (532 nm) for s-s, p-p, s-p left-to-right circular polarization and right-to-right circular polarization. Under the biphotonic action of 405 and 532 nm, the temporal evolution of the diffraction efficiency was strongly dependent on the polarization configuration of the recording beams. It was found that the blue-violet irradiation plays a dual role in holographic recordings: generation of merocyanine aggregation and induction of anisotropy. The experimental results were precisely fitted with a phenomenological model, assuming the simultaneous formation of one absorption grating induced by the 532 nm light and two coupling phase gratings generated from the refractive index changes by recording and auxiliary beams. The existence of absorption and phase gratings was proved by observing the florescence emission of holographic gratings and testing the dependence of the diffraction efficiency on the reading beam polarization state, respectively. The results provided a good deal of insight into the photochromic behavior of spirooxazine in polymers and created a new range of applications in the field of high-density optical storage.

Optical Gain from the Open Form of a Photochromic Molecule in the Solid State

This work presents evidence for line-narrowing from the UV photoexcited open form of the photochromic molecule, indolinospiropyran (1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro [2H-1-benzopyran-2,2'-(2H)-indole]) in the solid state. The line-narrowing is attributable to amplified spontaneous emission induced by optical gain and assisted by the waveguiding within the organic film. Optical gain throughout a band as large as 28 nm, with a maximum gain coefficient of 5.6 cm(-1), is observed in the merocyanine emission region (660-730 nm). These results open the way to the realization of hybrid devices based on the coupling between photochromic behavior and stimulated emission from conjugated molecules, such as lasing optical memories, and lasers gated by optical molecular switches.

Red-band holographic storage in azo dye sensitized by noncoherent light

Biphoton holographic storage recorded with 633-nm He-Ne beams has been investigated in Methyl Yellowdoped polystyrene film sensitized by weak noncoherent light from a low-pressure Hg lamp. It is demonstrated that the holography in the sample is erasable without fading. The dynamic behavior of the hologram is dependent on the cis-trans isomerization by noncoherent light and 633-nm beams and photoinduced heat.

Photophysical properties and photoisomerization processes of Methyl Red embedded in rigid polymer

The photophysical properties of Methyl Red molecules embedded in a poly(methyl methacrylate) (PMMA) matrix were investigated with photoinduced absorption, absorption kinetics, steady-state, and time-resolved luminescence spectroscopy. The excited singlet (S(1)) state lifetimes for trans and cis isomers of Methyl Red in PMMA at room temperature have been measured as 35 and 420 ps, respectively. The excited triplet (T(1)) state energy level and its lifetime at 77 K were also obtained. A slow trans-cis isomerization process having a time constant of a few hundred seconds was observed for the illuminated Methyl Red in rigid polymer. Based on measured photophysical properties and dynamic processes, an energy-level diagram for Methyl Red molecules in rigid polymer is introduced to explain these observations.