TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Claimed): Preparation of (I) comprises: reacting 9-thiophen-2-yl-9H-carbazole compound of formula (II) with benzo(1,2,5)thiadiazole compound of formula (III) to give (I).X = halo comprising Cl, Br or I; andR1a = 1-6C alkyl.Preferred Process: The reaction is performed in the presence of a palladium-containing catalyst. The reaction is performed at a temperature higher than 110 degrees C. (II) is obtained by: (1a) reacting a halo-thiophene compound of formula (V) in the presence of a base, with a carbazole compound of formula (VI) to obtain 9-thiophen-2-yl-9H-carbazole compound of formula (IV); and (2a) subjecting (IV) to lithiation and stannylation, to obtain (II). The step (1a) is performed in anhydrous dimethylformamide, at a temperature of 120-150 degrees C, for 2-8 hours. In step (2a), the lithiation and stannylation are performed sequentially in the same reaction environment. In step (2a), the lithiation is performed using n-butyl lithium or lithium di-iso-propylamide. In step (2a), the stannylation is performed through trialkylstannane of formula (R1a3SnX1a). The step (1a) is performed using a base comprising sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, cesium bicarbonate, dibasic sodium phosphate, dibasic potassium phosphate, tribasic sodium phosphate, tribasic potassium phosphate, sodium acetate, potassium acetate, sodium methylate, potassium methylate, sodium ethylate, potassium ethylate and potassium tertbutylate. (IVa) is subjected to lithiation and stannylation and the obtained (II) is (IIa).Y0 = Br or I;X1a = halo comprising Cl, Br or I; andR1a = 1-6C alkyl.Preferred Components: The catalyst is a palladium complex. The solvent is dimethylformamide or dimethyl sulfoxide. The palladium complex is prepared in situ. The amount of palladium used is 0.01-0.5 moles for 100 moles of dihalobenzothiadiazole (III). (II) is tri-n-butyl(2-(9'H-carbazol-9'-yl)thien-5-yl)stannane (IIa). (V) is 2-bromothiophene (Va). (VI) is carbazole (VIa) and (IV) is 2-(9'H-carbazol-9'-yl)-thiophene (IVa). The spectrum converter is in the form of a solar concentrator. SPECIFIC COMPOUNDS - 1 Compound (I) is specifically claimed i.e. 4,7-bis(5-carbazol-9-yl-2-thienyl)-2,1,3-benzothiadiazole of formula (Ia).    EXAMPLE - 4,7-Dibromo-2,1,3-benzothia-diazole (4.20 g), tri-n-butyl(2-(9'H-carbazol-9'-yl)thien-5-yl)stannane (19.2 g), dichlorobis(triphenylphosphine)palladium(II) (10.5 mg) and dimethyl formamide (100 ml) were added to a 250-ml, 3-necked flask, provided with bubble cooler, thermometer and nitrogen entry, under a nitrogen atmosphere. Still under nitrogen, the mixture was heated to 130 degrees C for 1 hour and then separated between toluene and water. The organic phase was dried, under magnetic stirring, on anhydrous sodium sulfate for 30 minutes and subsequently filtered. The solvent was removed in a rotary evaporator and the residue was crystallized from acetone/methyl tertbutyl ether. The crystals obtained were washed with methyl tertbutyl ether and dried in a rotary pump to give 4,7-bis(5-carbazol-9-yl-2-thienyl)-2,1,3-benzothiadiazole.