Abstract: A process for generation of acid uses a medium comprising a first acid-generating component capable of generating a first acid, and a secondary acid generator, this secondary acid generator being capable of thermal decomposition to form a secondary acid, the thermal decomposition of the secondary acid generator being catalyzed by the first acid. At least part of the medium is exposed to so as to cause formation of the first acid from the first acid-generating component; and the medium is then heated to cause, in the exposed part of the medium, acid-catalyzed thermal decomposition of the secondary acid generator and formation of the secondary acid.

Abstract: A process for generation of acid uses a medium comprising a first acid-generating component capable of generating a first acid, and a secondary acid generator, this secondary acid generator being capable of thermal decomposition to form a secondary acid, the thermal decomposition of the secondary acid generator being catalyzed by the first acid. At least part of the medium is exposed to so as to cause formation of the first acid from the first acid-generating component; and the medium is then heated to cause, in the exposed part of the medium, acid-catalyzed thermal decomposition of the secondary acid generator and formation of the secondary acid.

Abstract: A process for generation of acid uses a medium comprising a first acid-generating component capable of generating a first acid, and a secondary acid generator, this secondary acid generator being capable of thermal decomposition to form a secondary acid, the thermal decomposition of the secondary acid generator being catalyzed by the first acid. At least part of the medium is exposed to so as to cause formation of the first acid from the first acid-generating component; and the medium is then heated to cause, in the exposed part of the medium, acid-catalyzed thermal decomposition of the secondary acid generator and formation of the secondary acid.

Abstract: A process for producing an image uses an imaging medium comprising an acid-generating layer or phase comprising a mixture of a superacid precursor, a sensitizing dye and a secondary acid generator, and a color-change layer comprising an image dye. The sensitizing dye has first and second forms, the first form having substantially greater substantial absorption in a first wavelength range than the second form. The superacid precursor is not capable, in the absence of the first form of the sensitizing dye, of being decomposed by radiation in the first wavelength range. The secondary acid generator is capable of thermal decomposition, catalyzed by superacid, to form a secondary acid. While at least part of the sensitizing dye is in its first form, the medium is imagewise exposed to radiation in the first wavelength range, thereby causing, in the exposed areas of the acid-generating layer, the formation of superacid.

Abstract: Dyes comprising an inner salt of a compound of the formula:Q.sup.1 =Z-Q.sup.2wherein:Q.sup.1 is a 4-(benz[b]-4H-pyrylium)methylidene, 4-(benz[b]-4H-thiopyrylium)methylidene or 4-(benz[b]-4H-selenopyrylium)methylidene grouping;Z is a 1,3-(2-hydroxy-4-oxo-2-cyclobutylidene) hydroxide or 1,3-(2-hydroxy-4,5-dioxo-2-cyclopentylidene) hydroxide ring; andQ.sup.2 is a 4-(benz[b]-4H-pyran-4-ylidene)methyl, 4-(benz[b]-4H-thiopyran-4-ylidene)methyl or 4-(benz[b]-4H-selenopyran-4-ylidene)methyl grouping;wherein at least one of the groupings Q.sup.1 and Q.sup.

Abstract: A process for generation of acid uses a medium comprising a first acid-generating component capable of generating a first acid, and a secondary acid generator, this secondary acid generator being capable of thermal decomposition to form a secondary acid, the thermal decomposition of the secondary acid generator being catalyzed by the first acid. At least part of the medium is exposed to so as to cause formation of the first acid from the first acid-generating component; and the medium is then heated to cause, in the exposed part of the medium, acid-catalyzed thermal decomposition of the secondary acid generator and formation of the secondary acid.

Abstract: Squarylium compounds of the formula: ##STR1## (in which Q.sup.1 and Q.sup.2 are each a chromophoric group having an aromatic unsaturated system conjugated with the squarylium ring and such that in the compounds of formulae Q.sup.1 CH.sub.2 R.sup.1 and Q.sup.2 CH.sub.2 R.sup.2 the methylene hydrogens are active hydrogens, R.sup.1 and R.sup.2 are each independently a hydrogen atom or an aliphatic or cycloaliphatic group, and R.sup.3 and R.sup.4 are each independently a hydrogen atom, or an acyl, aliphatic, cycloaliphatic, aromatic or heterocyclic group, subject to the proviso that one of R.sup.3 and R.sup.4 may be an amino or substituted amino group, or one of R.sup.3 and R.sup.4 is a hydrogen atom and the other is an organosulfonyl group, or R.sup.3 and R.sup.4 together with the intervening nitrogen atom form a nitrogenous heterocyclic ring) are useful as near infra-red absorbers.

Abstract: Dyes comprising an inner salt of a compound of the formula:Q.sup.1 =Z-Q.sup.2wherein:Q.sup.1 is a 4-(benz[b]-4H-pyrylium)methylidene, 4-(benz[b]-4H-thiopyrylium)methylidene or 4-(benz[b]-4H-selenopyrylium)methylidene grouping;Z is a 1,3-(2-hydroxy-4-oxo-2-cyclobutylidene) hydroxide or 1,3-(2-hydroxy-4,5-dioxo-2-cyclopentylidene) hydroxide ring; andQ.sup.2 is a 4-(benz[b]-4H-pyran-4-ylidene)methyl, 4-(benz[b]-4H-thiopyran-4-ylidene)methyl or 4-(benz[b]-4H-selenopyran-4-ylidene)methyl grouping;wherein at least one of the groupings Q.sup.1 and Q.sup.

Abstract: Squarylium compounds of the formula: ##STR1## (in which Q.sup.1 and Q.sup.2 are each a chromophoric group having an aromatic unsaturated system conjugated with the squarylium ring and such that in the compounds of formulae Q.sup.1 CH.sub.2 R.sup.1 and Q.sup.2 CH.sub.2 R.sup.2 the methylene hydrogens are active hydrogens, R.sup.1 and R.sup.2 are each independently a hydrogen atom or an aliphatic or cycloaliphatic group, and R.sup.3 and R.sup.4 are each independently a hydrogen atom, or an acyl, aliphatic, cycloaliphatic, aromatic or heterocyclic group, subject to the proviso that one of R.sup.3 and R.sup.4 may be an amino or substituted amino group, or one of R.sup.3 and R.sup.4 is a hydrogen atom and the other is an organosulfonyl group, or R.sup.3 and R.sup.4 together with the intervening nitrogen atom form a nitrogenous heterocyclic ring) are useful as near infra-red absorbers.

Abstract: Squarylium compounds of the formula: ##STR1## (in which Q.sup.1 and Q.sup.2 are each a chromophoric group having an aromatic unsaturated system conjugated with the squarylium ring and such that in the compounds of formulae Q.sup.1 CH.sub.2 R.sup.1 and Q.sup.2 CH.sub.2 R.sup.2 the methylene hydrogens are active hydrogens, R.sup.1 and R.sup.2 are each independently a hydrogen atom or an aliphatic or cycloaliphatic group, and R.sup.3 and R.sup.4 are each independently a hydrogen atom, or an acyl, aliphatic, cycloaliphatic, aromatic or heterocyclic group, subject to the proviso that one of R.sup.3 and R.sup.4 may be an amino or substituted amino group, or one of R.sup.3 and R.sup.4 is a hydrogen atom and the other is an organosulfonyl group, or R.sup.3 and R.sup.4 together with the intervening nitrogen atom form a nitrogenous heterocyclic ring) are useful as near infra-red absorbers.

Abstract: 4-[3-(benz[b]pyran-4-ylidene)prop-1-enyl]benz[b]pyrylium, 4-[5-(4H-benz[b]pyran-4-ylidene)penta-1,3-dienyl]benz[b]pyrylium and 4-[7-(4H-benz[b]pyran-4-ylidene)hepta-1,3,5-trienyl]benz[b]pyrylium dyes, wherein at least one of the benzpyrylium nuclei carries at its 2-position a substituent in which a non-aromatic carbon atom is bonded directly to the benzpyrylium nucleus, subject to the proviso that if the or each 2-substituent contains an aromatic nucleus, this aromatic nucleus is not conjugated with the benzpyrylium nucleus, are useful as visible and near infra-red absorbers, having high extinction coefficients and a reduced tendency to develop absorptions at shorter wavelengths when dispersed in polymeric media.

Abstract: Squarylium compounds of the formula: ##STR1## (in which Q.sup.1 and Q.sup.2 are each a chromophoric group having an unsaturated system conjugated with the squarylium ring and such that in the compounds of formulae Q.sup.1 CH.sub.2 R.sup.1 and Q.sup.2 CH.sub.2 R.sup.2 the methylene hydrogens are active hydrogens, R.sup.1 and R.sup.2 are each independently a hydrogen atom or an aliphatic or cycloaliphatic group, and R.sup.3 and R.sup.4 are each independently a hydrogen atom, or an aliphatic, cycloaliphatic, aromatic or heterocyclic group, or one of R.sup.3 and R.sup.4 is a hydrogen atom and the other is an organosulfonyl group, or R.sup.3 and R.sup.4 together with the intervening nitrogen atom form a cycloaliphatic or aromatic ring) are useful as near infra-red absorbers.