TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The oxide semiconductor fine particles are made of titania, tin dioxide, tungsten oxide, zinc oxide, diniobium pentoxide, ferric oxide, zirconium oxide, magnesium oxide, cadmium sulfide, zinc sulfide, lead sulfide, bismuth sulfide, cadmium selenide and/or cadmium telluride. The porous film made of oxide semiconductor fine particles is sensitized with (I) and one or more further dyes, which is a metal complex dye and/or an organic dye comprising indoline, coumarin, cyanine, merocyanine, hemicyanine, methine, azo, quinone, quinonimine, diketo-pyrrolopyrrole, quinacridone, squaraine, triphenylmethane, perylene, indigo, xanthene, eosin and/or rhodamine.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Disclosed): Preparation of (I) comprises condensation of the corresponding pyridinium salt of formula (A-CH2-R2) and a ketone compound of formula (D-C(=O)-R1) to give (I) (where n is 1). Preferred Components: The dye is adsorbed together with an additive. The additive is a co-adsorbent, preferably a steroid, a crown ether, a cyclodextrin, a calixarene and/or a polyethyleneoxide. Preferred Definitions:    Z+ = N(R14)4+, Li+, Na+, K+ or -N+= which is part of (I) as part of group A;    R15, R19, R20, R21 = H;    Y1- = N-(-S(=O)2-CF3)2, B-(C6F5), CI-, Br-, I-, SCN-, BF4-, PF6-, ClO4-, SbF6-, AsF6-, SO3- or COO-;    NR18R19 = piperidinyl, piperazinyl, morpholinyl, imidazolidinyl or pyrrollidinyl (all optionally substituted by 1-20C alkyl, 1-20C alkylidene, benzo, trimethylene or tetramethylene); or    NR17R22, NR17R20, NR18R19, R17R18 = N-CH2-CH2-, N-CH2-CH2-CH2-, N-CH2-CH2-CH2-CH2-, N-CH2-CH2-O-, N-CH2-CH2-CH2-O-, N-CH2-CH2-NH-, N-CH2-CH2-CH2-NH-, N-CH2-CH2-S- or N-CH2-CH2-CH2-S-.    SPECIFIC COMPOUNDS - 15 Compounds (I) are specifically claimed e.g. 5-carboxy-2-((E)-2-(4-dimethylamino-phenyl)-vinyl)-1-methyl-pyridinium iodide of formula (Ia), 1-((E)-4,4-bis-(4-dimethylamino-phenyl)-buta-1,3-dienyl)-4-carboxy-pyridinium bromide, 5-carboxy-2-((E)-2-(4-(4-(2,2-diphenyl-vinyl)-phenyl)-1,2,3,3a,4,8b-hexahydro-cyclopenta(b)indol-6-yl)-vinyl)-1-methyl-pyridinium iodide, 5-carboxy-1-methyl-2-((E)-2-(1-(9-phenyl-9H-carbazol-3-yl)-2,3-dihydro-1H-indol-6-yl)-vinyl)-pyridinium iodide and 5-carboxy-4-hexyloxy-1-methyl-2-((E)-2-(4-morpholin-4-yl-phenyl)-vinyl)-pyridinium iodide.    EXAMPLE - 5-Methoxycarbonyl-1,2-dimethyl-pyridinium iodide (890 mg), 4-dimethylaminobenzaldehyde (500 mg), piperidine (26 mg) and acetic acid (18.2 mg) were dissolved in toluene (10 ml) and the solution was stirred at 110 degrees C for 15 hours. After cooling down to the room temperature, the reaction mixture was concentrated under reduced pressure and purified to give 2-((E)-2-(4-dimethylamino-phenyl)-vinyl)-5-methoxycarbonyl-1-methyl-pyridinium iodide. A mixture of 2-((E)-2-(4-dimethylamino-phenyl)-vinyl)-5-methoxycarbonyl-1-methyl-pyridinium iodide (100 mg) and hydrobromic acid (3 ml, 48% in water) was stirred at 60 degrees C for 18 hours. After cooling down to the room temperature, the reaction mixture was concentrated under reduced pressure. The crude product was purified to give 5-carboxy-2-((E)-2-(4-dimethylamino-phenyl)-vinyl)-1-methyl-pyridinium iodide (59 mg, 61%).