Benzopyrylium Salt Photopolymer Dyes for Visible-Range Bleachability
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Solution Overview
Problem
Existing photopolymer compositions do not achieve satisfactory bleachability, particularly in the visible spectral range from 400 nm to 800 nm, despite having good holographic performance with known dyes.
Innovation Solution
Incorporating benzopyrylium salts as dyes in photopolymer compositions, specifically with certain structural and molecular weight characteristics, enhances bleachability and diffraction efficiency, allowing high transmission across the visible spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If known dyes are used in photopolymer compositions, then good holographic performance is achieved, but satisfactory bleachability in the visible spectral range (400 nm to 800 nm) is not achieved
Solution Approach 1:
The patent changes the chemical parameters of the dye by introducing specific substituents (electron-donating groups like dialkylamino, alkyl, or aryl groups at positions 2 and 7 of the xanthylium core) and selecting specific anions with molecular weights ≥200 g/mol that do not contain halogen atoms. These parameter changes result in benzopyrylium salts that maintain good holographic performance while achieving satisfactory bleachability across the visible spectral range.
Solution Approach 2:
The patent creates a composite photoinitiation system combining benzopyrylium salt dyes with specific co-initiators (triarylalkylborate salts or tertiary amines). This composite approach allows the dye component to provide both holographic performance and improved bleachability, while the co-initiator enables rapid radical polymerization initiation through electron or energy transfer mechanisms.
2Object-affected harmful factors
If dyes are selected for good bleachability, then transmission over the visible spectral range is improved, but rapid initiation of radical polymerization may be compromised
Solution Approach 1:
The patent introduces a co-initiator as an intermediary substance that mediates between the benzopyrylium salt dye and the writing monomers. The co-initiator (triarylalkylborate salt or tertiary amine) accepts energy or electrons from the excited dye and transfers them to the monomer, enabling rapid radical polymerization initiation. This intermediary mechanism allows the dye to be optimized for bleachability while the co-initiator ensures rapid initiation speed.
Solution Approach 2:
The patent optimizes the molecular weight parameter of the anion (≥200 g/mol, preferably ≥250 g/mol or ≥300 g/mol) to balance bleachability and initiation performance. Heavier anions without halogen atoms provide better bleachability while the specific chemical structure maintains compatibility with co-initiators for rapid polymerization initiation.
3Productivity
If conventional dyes are used, then photopolymerization can be initiated, but inhomogeneities or turbidities may form in the photopolymer
Solution Approach 1:
The patent changes the chemical parameters of the dye structure by introducing specific substituents (dialkylamino, alkyl, or aryl groups at positions 2 and 7) and selecting anions with molecular weights ≥200 g/mol that do not contain halogen atoms. These parameter changes improve compatibility with photopolymer composition components, preventing inhomogeneities and turbidities while maintaining effective polymerization initiation.
Solution Approach 2:
The patent creates a composite photoinitiation system where the benzopyrylium salt dye and co-initiator work synergistically. This composite approach ensures better compatibility with the photopolymer matrix components, preventing phase separation and turbidity formation while maintaining high polymerization efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of benzopyrylium salts in photopolymer compositions results in improved bleachability and diffraction efficiency, achieving high transmission and compatibility with other components, thereby enhancing holographic performance.
Implementation Method 1
a photoinitiator system (PIS), wherein the PIS contains at least one benzopyrylium salt according to the invention as a dye
Implementation Method 2
rapid initiation of a radical polymerization by electron or energy transfer with a suitable co-initiator
Implementation Method 3
the interference field composed of signal light beam and reference light beam (that of two plane waves in the simplest case) is mapped into a refractive index grating by the local photopolymerization of writing monomers
Implementation Method 4
By illuminating the hologram with only the reference light beam, the signal can then be reconstructed
Data Source
AI summary
The disclosure relates to a benzopyrylium dye of the formula (I),in which R200, R201, R202, R203, R204, R205, R206, R207 and R208 independently of one another are each hydrogen, C1 to C16 alkyl, C4 to C7 cycloalkyl, C7 to C16 aralkyl, C6 to C10 (het)aryl, hydroxyl, C1 to C6 alkoxy, or dialkylamino, the dialkylamino being selected from the group consisting of diethylamino, dimethylamino, diisopropylamino, a six-membered saturated ring attached via the N of the amino group, which may additionally contain an N or O and may be substituted by nonionic arbitrary radicals, or a combination of at least two thereof, and/or R200 with R201 or R201 with R202 or R202 with R203 and/or R205 with R206 and/or R206 with R207 each independently of one another form a —CH═CH—CH═CH— bridge, and A is a —CH2— or a —CH2—CH2— bridge, where the anion Ann− has a molecular weight of ≥200 g/mol and does not contain a halogen atom.