TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Device: In device (D1), the light-emitting layer further comprises a guest emitting material comprising a transition metal complex.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The guest emitting material is blue, green or red phosphorescent and transition metal of the transition metal complex is iridium (Ir), platinum (Pt), osmium (Os), copper (Cu), rhodium (Rh), europium (Eu) or ruthenium (Ru).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Disclosed): Preparing conjugated compound involves refluxing 2-bromo-benzoic acid methyl ester, carbazole, potassium carbonate, sodium sulfate and copper powder in presence of nitrobenzene; heating and stirring at refluxing temperature for 24 hours and nitrobenzene is removed by reduced pressure distillation; after work up 2-carbazol-9-yl-benzoic acid ethyl ester is obtained which on dissolving in tetrahydrofuran and lithium reagent carried out in nitrogen environment; and adding ammonium chloride saturated solution to terminate the reaction gives conjugated compound of formula (I') containing hydroindoloacridine structural element. Preferred Definitions:    aryl=phenyl, naphthyl, diphenyl, anthryl, pyrenyl, phenanthryl, fluorine or multi-phenyl group;and    heterocyclic ring=pyrane, pyrroline, furan, benzofuran, thiophene, benzothiophene, pyridine, quinoline, isoquinoline, pyrazine, pyrimidine, pyrrole, pyrazole, imidazole, indole, thiazole, isothiazole, oxazole, isoxazole, benzothiazole, benzoxazole, 1,2,4-triazole, 1,2,3-triazole, 1,2,3,4-tetraazole phenanthroline or heterocyclic aryl group.    SPECIFIC COMPOUNDS - 4 Compounds are disclosed as (I) i.e. 8,8-bis-(4-tert-butyl-phenyl)-8H-indolo(3,2,1-de)acridine (Ia), 8,8-bis-(4-triphenylsilanyl-phenyl)-8H-indolo(3,2,1-de)acridine, 8,8-bis-(4-bromo-phenyl)-8H-indolo(3,2,1-de)acridine or 8,8-bis-(4'-triphenylsilanyl-biphenyl-4-yl)-8H-indolo(3,2,1-de)acridine.    EXAMPLE - No suitable example is given.