Couplers in colour photography—chemistry and function Part 3

Abstract

Part 3 of the review (Parts 1 and 2 were in the preceding Issue) comprises a detailed representation of tools contributing to ‘image quality’ in a broad sense. Section 1 covers a group of two-equivalent couplers whose function consists in maintaining an otherwise inaccessible level of image quality by release of ‘photographically useful groups’, usually represented by the acronym ‘PUG’. PUGs such as development inhibitors released from a DIR coupler, development activators, electron-transfer agents and bleach activators are capable of upgrading image quality by increasing speed and exposure latitude, reducing graininess, enhancing edge reproduction and colour contrast, but also stability to varying process conditions. In most cases their action depends on imagewise release and carefully controlled diffusibility within the developing layers. The variety of chemical concepts represents the complexity of the photographic tasks.

In a different sense, masking couplers (Section 2) are used as an important tool for improving colour reproduction by compensating the side absorptions of necessarily imperfect image dyes and extending the recorded colour gamut.

Chemical aspects of the dark stability and light stability of the coloured image and industrially used additives for extending its ‘lifetime’ are presented in Section 3. Section 4 considers the high degree of technological ripeness of photographic systems based on chemistry and presents an outlook on their future perspectives with respect to the erosion of their market by digital photography.

Keywords:

• acidic NH heterocycles
• active esters
• 4-alkoxyphenylthiomorpholine-S,S-dioxides
• alkylidenebisphenols
• 1-alkyl-5-mercaptotetrazoles
• 3-alkylmercapto-1,2,4-triazoles
• arenesulphinates
• 4-arylazo-1-naphthol-2-carbonamide
• 4-arylazopyrazolone
• bleach stain
• BAR (bleach accelerator releasing) couplers
• benzo(1,2,4-thiadiazine-1,1-dioxide)-3-acetanilides
• benzotriazoles
• bleach activator
• bleach inhibitor
• t-butylhydroquinone monoether
• DAR (development activator releasing) couplers
• dark fading
• development activator
• development inhibitor
• development restrainer
• dialkoxyspiroindane
• DIAR (development inhibitor anchimeric releasing) couplers
• diffusibility
• diffusing dye releasing couplers
• monoalkylation products of 2,5-dimercapto-1,3,4-thiadiazole
• DIR (development inhibitor releasing) couplers
• DIR indanones
• DIRR (development inhibitor redox releasing) couplers
• dye aggregation
• electron-transfer agent
• epoxides
• ETAR (electron-transfer agent releasing) couplers
• excited singlet state ¹S₁
• extra-dye releasing couplers
• fogging agent
• ‘Förster type’ energy transfer
• heterocyclic thiol
• high-dye-yield coupler
• hydrolysable development inhibitor
• 6-hydroxychromans
• 5-hydroxycumarans
• hydroxyphenylbenzotriazole
• image stabilizer
• indoaniline dyes
• induction period
• inter-layer interimage effects
• intersystem crossing rate
• light fading
• malonanilides
• masking couplers
• masks
• 2-mercapto-1,3,4-oxadiazoles
• 5-mercapto-1,2,3-triazole
• NAR/FAR (nucleating or fogging agent releasing) couplers
• nucleating agent
• oxidizable timing group
• 4-oxoquinazoline-2-acetanilides (quinazoloneacetanilides)
• 1-phenyl-5-mercaptotetrazole
• photochemical sensitizers
• photodeactivator
• photodegradatation
• photographically useful (leaving) groups (PUG)
• photographic diffusibility
• quenchers
• scavenger releasing couplers (SCRC)
• singlet oxygen (¹Δ) stability stain problem
• SMR (soluble mercaptan releasing) couplers
• sulphenic acid equivalent
• 2,2,6,6-tetramethyl-4-hydroxypiperidine
• timing group
• 1,2,3-triazoles
• triplet state
• two-step mechanism (reaction)
• UV absorber