TECHNOLOGY FOCUS - ELECTRONICS - Preferred Composition: The organic optoelectronic device comprises organic thin film (105) formed between anode (120) and cathode (110). The organic thin film is chosen from light-emitting layer (130), hole-transport layer, hole-injection layer, electron-transport layer, electron-injection layer and hole-blocking layer.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The fluorene derivative (I) is preferably of formula (II), (III), (IV) or (V).Ar1,Ar2=3-30C aryl or 2-30C heteroaryl (both optionally substituted), preferably phenyl, naphthalenyl, fluorenyl, biphenyl, dibenzo furanyl, dibenzothiophenyl, anthracenyl, phenantryl, pyrenyl, biphenyl, N-terphenyl, chrysenyl, triphenylenyl, perylenyl, indenyl, furanyl, thiophenyl pyrrolyl, pyrazolyl, imidazolyl, triazolyl, oxazolyl, thiazolyl, thiadiazoyl, pyridyl, pyrimidinyl, pyrazinyl, triazinyl, benzofuranyl, benzothiophenyl, benzimidazolyl, indolyl, quinolinyl, isoquinolinyl quinazolinyl quinoxalinyl, naphtharidinyl, phenazinyl, phenotiazinyl or phenoxazinyl (all optionally substituted);X1=NR', O, S or P;R'=H, or 1-20C alkyl, 6-30C aryl or 3-30C heteroaryl (all optionally substituted);n=0 or 1;andR5-R9=H, or 1-6C alkyl, 6-30C aryl, or 2-30C heteroaryl (all optionally substituted). Preferred Definitions:    ETU=imidazolyl, triazolyl, tetrazolyl, oxadiazolyl, oxatryazolyl, benzimidazolyl, benzotriazolyl, pyridinyl, pyrimidinyl, triazinyl, pyrazinyl, pyridazinyl, purinyl, quinolinyl, isoquinolinyl, phthalazinyl pyridinyl, quinoxalinyl, quinazolinyl, acridinyl, phenanthrolinyl, phenazinyl, or triphenylinyl.    SPECIFIC COMPOUNDS - 31 Fluorene compounds e.g. 4-((3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)diphenylmethyl)-N,N-diphenylfluorene of formula (Ia), N-(4-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)-9-phenyl-9H-fluoren-9-yl)phenyl)-4-phenyl-N-(4-phenylphenyl)fluorene, 4-((3-(4,6-bis(4-phenylphenyl)-1,3,5-triazin-2-yl)phenyl)diphenylmethyl)-N,N-diphenylfluorene, N-(9,9-dimethyl-9H-fluoren-2-yl)-2'-(4,6-diphenyl-1,3,5-triazin-2-yl)-N-phenyl-9,9'-spirobi(fluorene)-6-amine and 4-phenyl-N-(4-(9-phenyl-2-(triphenylen-2-yl)-9H-fluoren-9-yl)phenyl)-N-(4-phenylphenyl)fluorene, are specifically claimed.