Soaps and cleansing compositions contain a compound, of the general formula <FORM:0611510/III/1> (wherein A represents an aromatic nucleus which may contain substituents and of which two vicinal carbon atoms are attached to the two nitrogen atoms of the imidazole ring, R1 represents hydrogen or a substituent, e.g. an alkyl or aralkyl residue, and R represents a radical containing an uninterrupted series of at least four conjugated double bonds starting with the carbon atom of the residue R directly connected to the m carbon atom, said double bonds being present in open chains or in rings), which exhibits a blue to violet fluorescence in ultra-violet light, imparts little or no colour to material treated therewith and is sparingly soluble or insoluble in water. In examples: (2) a : b -di-(benzimidazyl-2)-ethylene, or a solution thereof in caustic soda solution or in glycol monomethyl ether, is added to a melted soap mass; (4) and (7) the same compound is added to the sodium salt of sulphonated 2-heptadecyl-N-benzyl- or -N-methyl-benzimidazole. Other washing agents specified for use with the fluorescent materials are monocarboxylic esters of 4-sulphophthalic acid with higher fatty alcohols, fatty alcohol sulphonates, and condensation products of higher fatty acids with aliphatic hydroxy- and amino-sulphonic acids. A sample has been furnished under Sect. 2 (5) of cotton fabric boiled with a solution of soap containing the di-imidazole compound obtained by condensing terephthalic aldehyde with excess of 2-methylbenzimidazole.ALSO:Artificial threads or films, e.g. of regenerated cellulose, cellulose acetate or synthetic linear superpolyamide, are improved in colour or whiteness by adding to the spinning or casting solution a compound of the general formula <FORM:0611510/IV(a)/1> (wherein A represents an aromatic nucleus which may contain substituents and of which two vicinal carbon atoms are attached to the two nitrogen atoms of the imidazole ring, R1 represents hydrogen or a substituent, e.g. an alkyl or aralkyl residue, and R represents a radical containing an uninterrupted series of at least four conjugated double bonds starting with the carbon atom of the residue R directly connected to the m -carbon atom, said double bonds being present in open chains or in rings), which exhibits a blue to violet fluorescence in ultra-violet light, imparts little or no colour to the material, and is sparingly soluble or insoluble in water. Particular classes of substances which are suitable are: (A) compounds of the above formula in which R represents an aralkenyl residue of which the alkenyl residue contains at least one double bond which forms with the double bond of the imidazole ring and those of the aryl nucleus an uninterrupted series of at least five conjugated double bonds e.g. a 2-styrylbenzimidazole obtainable by condensation of a 2-methylbenzimidazole with an aromatic aldehyde, the aryl nuclei of these components optionally containing substituents (e.g. acylated amino groups); (B) compounds of the above formula in which R represents a heterocyclic residue containing the required series of conjugated double bonds, e.g. diimidazoles of the formula <FORM:0611510/IV(a)/2> such as dibenzimidazoles (in which A represents a benzene nucleus) obtainable by known methods from o-phenylenediamines which may contain further nuclear substituents; (C) compounds of the formula <FORM:0611510/IV(a)/3> wherein R2 represents a divalent residue containing at least one double bond which forms with the >C=N- double bonds of the imidazole rings and the double bonds of the aromatic nuclei A an uninterrupted series of conjugated double bonds, e.g. (a) substituted ethylenes (in which R2 is CH=CH) obtainable by condensing aromatic o-diamines with fumaric or maleic acid or functional derivatives thereof, and (b) compounds in which R2 represents a divalent aromatic or heterocyclic residue containing at least one double bond in conjugation with the >C=N- double bonds, obtainable similarly from aromatic or heterocyclic dicarboxylic acids or their functional derivatives.ALSO:2-Styrylbenzimidazoles are prepared by condensing a 2-methylbenzimidazole with an aromatic aldehyde. Di-imidazylethylenes of the general formula <FORM:0611510/IV(b)/1> (wherein A represents an aromatic nucleus and R1 hydrogen or a substituent, e.g. benzyl) are prepared by condensing aromatic o-diamines with fumaric or maleic acid or functional derivatives thereof, e.g. o-phenylenediamine with fumaric acid to produce a : b -di(benzimidazyl-2)-ethylene, or with maleic acid or anhydride. Di-imidazyl compounds containing, in place of the -CH=CH- group in the foregoing general formula, a divalent aromatic or heterocyclic residue containing at least one double bond in conjugation with the >C=N- double bonds of the imidazole rings are obtainable similarly using aromatic or heterocyclic dicarboxylic acids or their functional derivatives in place of the fumaric or maleic compounds. A compound employed in the preparation of a sample furnished under Sect. 2 (5) was prepared by condensing terephthalic aldehyde with excess of 2-methylbenzimidazole.ALSO:Materials in the form of fibres or films are improved in colour or whiteness by applying thereto, at any desired stage in their manufacture or treatment, a compound, of the general formula <FORM:0611510/IV (c)/1> wherein A represents an aromatic nucleus which may contain substituents and of which two vicinal carbon atoms are attached to the two nitrogen atoms of the imidazole ring, R1 represents hydrogen or a substituent, e.g. an alkyl or aralkyl residue, and R represents a radial containing an uninterrupted series of at least four conjugated double bonds starting with the carbon atom of the residue R directly connected to the m -carbon atom, said double bonds being present in open chains or in rings), which exhibits a blue to violet fluorescence in ultra-violet light, imparts little or no colour to insoluble in water. Particular classes of substances which are suitable are: (a) compounds of the above formula in which R represents an aralkenyl residue of which the alkenyl residue contains at least one double bond which forms with the double bond of the imidazole ring and those of the aryl nucleus an uninterrupted series of at least five conjugated double bonds, e.g. 1 2-styrylbenzimidazole obtainable by condensation of a 2-methylbenzimidazole with an aromatic aldehyde, the aryl nuclei of these components optionally containing substituents (e.g. acylated amino groups); (b) compounds of the above formula in which R represents a heterocyclic residue containing the required series of conjugated double bonds, e.g. di-imidazoles of the formula <FORM:0611510/IV (c)/2> such as dibenzimidazoles (in which A represents a benzene nucleus) obtainable by known methods from o-phenylenediamines which may contain further nuclear substituents; (c) compounds of the formula <FORM:0611510/IV (c)/3> (wherein R2 represents a divalent residue containing at least one double bond which forms with the >C=N- double bonds of the imidazole rings and the double bonds of the aromatic nuclei A an uninterrupted series of conjugated double bonds, e.g. (a) substituted ethylenes (in which R2 is CH=CH) obtainable by condensing aromatic o-diamines with fumaric or maleic acid or functional derivatives thereof, and (b) compounds in which R2 represents a divalent aromatic or heterocyclic residue containing at least one double bond in conjugation with the >C=N- double bonds, obtainable similarly from aromatic or heterocyclic dicarboxylic acids or their functional derivatives. Compounds in which R1 represents hydrogen may be used in the form of metal (especially alkali metal) salts, in which case they may be dissolved in an alcoholic solution of an alkali hydroxide and the solution, after dilution with water, may be applied to the material to be treated, e.g. natural or regenerated cellulose, which is then rinsed, centrifuged or squeezed and dried. Alternatively the material may be impregnated with a solution of the fluorescent compound (including one in which R1 is a substituent) or a salt thereof in an organic solvent (which is then removed) or with a dispersion thereof (e.g. one obtained with the aid of a dispersing agent such as soap, a saponaceous substance, polyglycol ethers of fatty alcohols, sulphite cellulose waste liquor or condensation products of alkylnaphthalenesulphonic acids and formaldehyde). The fluorescent compounds may also be applied during the manufacture of the materials to be improved, e.g. by incorporating them in paper pulp or in a viscose solution for the production of films or threads or other spinning masses (e.g. containing a linear synthetic polyamide or cellulose acetate), or they may be used in admixture with assistants used to improve textile materials, e.g. with washing agents such as soaps, salts of sulphonated washing agents, e.g. sulphonated benzimidazoles substituted in the 2-position by higher alkyl residues, monocarboxylic esters of 4-sulphophthalic acid with higher fatty alcohols, fatty alcohol sulphonates or condensation products of higher fatty acids with aliphatic hydroxy- or amino-sulphonic acids, or with chemical bleaching agents, e.g. sodium hypochlorite, or with mercerizing liquor, or in discharge printing pastes. The process is applicable to the improvement of cellulosic materials such as cellulose or paper, textile materials of cotton, linen or regenerated cellulose, natural or artificial nitrogenous materials such as wool, silk or synthetic polyamide fibres, cellulose acetate, and synthetic materials produced by polymerization, all of which materials may be undyed or dyed or printed. Examples are given of a large number of applications of the process, the fluorescent materials used being a : b - di - (benzimidazyl - 2) - ethylene (obtai