Sensitizer dyes for photoacid generating systems

Abstract

Photosensitizing dyes are often used in conjunction with a photoacid generator in holographic recording media. Conventional photosensitizing dyes typically are limited by having an appreciable absorption of light when used in a sufficient concentration, such that the intensity of light decreases significantly with penetration into a recording medium. The present invention discloses a number of new 5-alkynyl substituted napthacene photosensitizing dyes that have low extinction coefficients coupled with good sensitizing properties, such that the problems associated with the photosensitizing dyes absorbing light are significantly reduced.

Description

RELATED APPLICATION [0001] This application is a continuation of and claims priority to International Application No. PCT / US2003 / 040865, which designated the United States and was filed on Dec. 22, 2003, published in English, which claims the benefit of U.S. Provisional Application No. 60 / 436,517, filed Dec. 23, 2002. The entire teachings of the above applications are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] Photoacid generation has become valuable in the fields of photoresists and cationic polymerization. Cationic photopolymerization has developed into an excellent alternative to free-radical photopolymerization for applications that can take advantage of the high speed, low temperature, and environmental friendliness of radiation curing technology. In contrast with radiation curing processes initiated by free radicals, cationic photopolymerization processes are not inhibited by oxygen, and by employing monomers and oligomers such as epoxides and oxetanes...

AI Technical Summary

Benefits of technology

[0010] This invention provides a series of novel 5-alkynyl substituted naphthacene dyes. This invention further provides such dyes that are efficient photosensitizers for onium salt photoacid generators (PAGs) when exposed to actinic radiation. Additionally, such dyes further exhibit desirably low extinction coefficients, thus making it possible to employ the dyes of the present invention within thicker layer of recordable media than previously achievable (Example 5). This invention also provides a process for use of these dyes for the uniform polymerization of thick media. Even further, this invention provides a process or method for the utilization of these dyes for the recording of holograms with good recording sensitivity and good image fidelity. Holographic recording media (HRM) comprising inventive dyes of the present invention showed high signal-to-noise ratio for a given number of images (as indicated by high cumulative grating strength) and achieved recording sensitivity better than an HRM of the same thickness comprising a sensitizing dye of prior art (Example 6). The enhanced recording sensitivity exhibited by use of a sensitizer of the present invention is more advantageous as the thickness of the recording media is increased further, as the limitations due to low concentration of the dye become more severe.

[0036] Advantages of the present invention include photosensitizer dyes with low extinction coefficients when exposed to visible light. As a consequence, holographic recording media having a thickness greater than about 300 micrometers, and which exhibit good recording sensitivity and good image fidelity, can be prepared with these dyes. These photosensitizer dyes also bleach upon exposure to visible light when in the presence of a photoacid generator.

Problems solved by technology

Increasing the thickness of the media, however, results in an increase in the absorption of the medium, thereby increasing the optical path length of the medium.

Increasing the concentration of the photosensitizer dye, however, results in an increase in the absorption of the medium, thereby increasing the optical path length of the medium.

The absorbance of the medium can cause undesirable tradeoffs such as non-uniform polymerization throughout the volume of a polymerizable medium, impaired fidelity of holograms recorded in such media and a diminished increase in the dynamic range of a holographic recording medium as a function of increasing the medium's thickness.

The decrease in light intensity with depth into the medium from the front surface of the medium leads to non-uniformity of the extent of polymerization that occurs within the medium, so that less polymerization occurs depthwise in the interior of a medium as compared to at or near the front surface that is exposed to the incident light.

Such methods typically result in formation of holograms that exhibit diffraction efficiency less than about 0.05% and which are required to exhibit both good angular selectivity characteristics and good image quality.

At concentrations that generate both a useful amount of polymerization and high recording sensitivity, presently available photosensitizer dyes are limited to use in polymerizable media with thicknesses of about 300 micrometers or less.

Presently available photosensitizer dyes such as rubrene and 5,12-bis(phenylethynyl)naphthacene (BPEN) have extinction coefficients at specific wavelengths of visible light, especially light in the 500-550 nm region (e.g., from commercially-available lasers such as an argon ion laser or frequency-doubled Nd:YAG laser) that result in reduced performance when used in relatively thick holographic recording media having thicknesses greater than about 300 micrometers.

In addition, photosensitizer dyes should have adequate solubility, especially in cationic polymerization media, and should not inhibit cationic processes (e.g., should be sufficiently non-basic).

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