NOVELTY - Carbazole-containing compounds (I) are new.    USE - (I) are useful in organic light emitting device, which is useful in consumer product (all claimed) including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants, laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, and a sign. (I) are useful in optoelectronic devices such as organic solar cells and organic photodetectors, and organic devices such as organic transistors.    ADVANTAGE - (I) have improved charge balance and charge stability, and provide improved film formation during device production. (I) have improved blocking properties, impeding properties, and transport properties for both holes and electrons depending upon the relative energy and relative mobility. (I) provide device with: improved stability while maintaining high triplet energy; reduced oxidation potentials; and improved electrochemical reversibility.    DETAILED DESCRIPTION - Carbazole-containing compounds of formula (I) are new.    a = 1-20;    b = 0-20;    m, n = 0-2, where m+n is at least 1;    X = biphenyl, terphenyl, naphthalene, triphenylene, phenanthrene, fluorene, chrysene, dibenzothiophene, dibenzofuran, benzofuran, benzothiophene, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, indole, benzimidazole, indazole, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine or thienodipyridine (all substituted by R); and    R = H, alkyl, heteroalkyl, benzene, biphenyl, terphenyl, naphthalene, phenalene, phenanthrene, fluorene, chrysene, dibenzothiophene, dibenzofuran, benzofuran, benzothiophene, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, indole, benzimidazole, indazole, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine or thienodipyridine.    An INDEPENDENT CLAIM is included for an organic light emitting device (I), comprising an anode; a cathode; and a first organic layer disposed between the anode and the cathode, where the organic layer comprises (I).