TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The chromophore is a metal complex of formula ((L)n3(L1a)n4M(Hal)n5) (14a) or ((L2a)n6M1a) (16a). The photoactive semiconductor porous material is titanium dioxide (TiO2) (preferred), tin(II)oxide (SnO2), zinc oxide (ZnO), niobium pentoxide (Nb2O5), zirconium oxide (ZrO2), cerium(IV) oxide (CeO2), tungsten (VI) trioxide (WO3), chromium(III)oxide (Cr2O3), chromium dioxide (CrO2), chromium trioxide (CrO3), silicon dioxide (SiO2), iron(III)oxide (Fe2O3), copper(II) oxide (CuO), aluminum oxide (Al2O3), copper aluminum oxide (CuAlO2), strontium titanate (SrTiO3), strontium copper oxide (SrCu2O2) and/or zirconium titanate (ZrTiO4). The photoactive semiconductor porous material: has a thickness of 1-100 mu m, preferably 5-30 mu m; consists of layers; contains particles having an average diameter or length of 1-40 nm, preferably 15-30 nm; and is a mixture of at least a first and second kind of particles, where the first kind of particles have an average diameter or length of 1-30 nm and the second kind of particles have an average diameter of 30-100 nm and/or a length of 100 nm to 5 mu m.M = ruthenium (Ru) (preferred), osmium (Os) or iridium (Ir);Hal = Cl, Br, I, CN or -NCS (preferred);n3, n4, n5 = 0-4, preferably 2-3;L, L1a = organic heterocyclic ligands containing N atoms which are linked by N-atoms to the respective metal M, where either one of L and L1a, or both L and L1a are linked to the acyloin group by any of the C-atoms within the ligands;M1a = palladium (Pd) (preferred), platinum (Pt) or nickel (Ni);n6 = 0-4, preferably 1-2; andL2a = organic heterocyclic ligand containing nitrogen atoms, where the ligand is linked by several of the N-atoms to the respective metal M1a, and the ligand is linked to the acycloin group by any of the C-atoms within the ligand.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The device further comprises a photoactive semiconductor porous material. The device contains a charge-transporting agent, which is a liquid, ionic liquid, or polymer gel based or solid state electrolyte. The device further comprises at least one other dye, which is ruthenium complex compounds of formula (15a), (27a), (28a), (29a), (30a), (31a) or (32a).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Disclosed): Preparation of (I) comprises: reacting chromophore compounds of formula (a) with substituted cyclobut-2-enone compounds of formula (b) to give chromophore substituted cyclobut-2-enone compounds of formula (c); and reacting (c) to give chromophore substituted 2-hydroxy-cyclobut-2-enone compounds of formula (d) (representative of (I)).E1 = Cl or alkoxy (preferably ethoxy, propoxy, iso-propoxy or butoxy).Preferred Components: (I) is chemisorbed to the photoactive semiconductor porous material. SPECIFIC COMPOUNDS - 11 Compounds (I) are specifically claimed e.g. 3-((3,3-dimethyl-1-propyl-1,3-dihydro-2H-indol-2-ylidene)methyl)-4-hydroxycyclobut-3-ene-1,2-dione of formula (Ia), 3-(1-hexyl-5-(5-hexyl-thiophen-2-yl)-3,3-dimethyl-1,3-dihydro-indol-(2E)-ylidenemethyl)-4-hydroxy-cyclobut-3-ene-1,2-dione, 3-(1,1-dimethyl-3-propyl-1,3-dihydro-benzo(e)indol-(2E)-ylidenemethyl)-4-hydroxy-cyclobut-3-ene-1,2-dione, 3-(5-(4'-(1-ethyl-propoxy)-biphenyl-4-yl)-1-hexyl-3,3-dimethyl-1,3-dihydro-indol-(2E)-ylidenemethyl)-4-hydroxy-cyclobut-3-ene-1,2-dione and 3-(5-(5-tert-butyl-thiophen-2-yl)-1-hexyl-3,3-dimethyl-1,3-dihydro-indol-(2E)-ylidenemethyl)-4-hydroxy-cyclobut-3-ene-1,2-dione.    EXAMPLE - An equimolar amount of 2,3,3-trimethyl-1-propyl-2,3-dihydro-1H-indolium iodide and 3,4-diethoxy-cyclobut-3-ene-1,2-dione in ethanol were heated in presence of small amount triethylamine to 70 degrees C for 4 hours. The solvent was removed and worked up to give 3-((3,3-dimethyl-1-propyl-1,3-dihydro-2H-indol-2-ylidene)methyl)-4-ethoxycyclobut-3-ene-1,2-dione (xx). To (xx) in ethanol, aqueous sodium hydroxide was added and the mixture stirred for 2 hours at 50 degrees C. After cooling, aqueous hydrochloric acid was added and the solvent was removed and worked up to give 3-((3,3-dimethyl-1-propyl-1,3-dihydro-2H-indol-2-ylidene)methyl)-4-hydroxycyclobut-3-ene-1,2-dione.