Full Definitions:    R1-R10=H, D, halo, 6-60C aryl, fluorenyl, 3-60C aliphatic ring, C6-60C aromatic fused ring, 2-60C heterocyclic including hetero atoms chosen from O, N, S, Si and P, -L-N(R')(R"), 1-50C alkyl, 2-20C alkenyl, 1-30C alkoxy, 6-30C aryloxy, in which any one of R1-R4,R7-R10 combines with neighboring group to form ring;    X,Y'=S, O, or -Si(R11)(R12);    R11,R12=H, 6-60C aryl, fluorenyl, 2-60C hetero ring containing hetero atoms chosen from O, N, S, Si and P, or 1-50C alkyl;    m,n=0 or 1;    m+n=1 or more;    L=single bond, 6-60C arylene, fluorenyl, 2-60C hetero ring including hetero atoms chosen from O, N, S, Si and P or bivalent aliphatic hydrocarbyl optionally substituted by nitro, cyano, halo, 1-20C alkyl, 6-20C aryl, 2-20C hetero ring group, 1-20C alkoxy, or amino;    Ar1=2-60C hetero ring group including hetero atoms chosen from O, N, S, Si and P, 6-60C aryl, fluorenyl, or -N(R')(R");and    R',R"=2-60C hetero ring group including hetero atoms chosen from O, N, S, Si, and P, 6-60C aryl, or fluorenyl.    (i) When R1-R4 are H, at least one of R7-R10 is not hydrogen; (ii) When R7-R10 are hydrogen, at least one of R1-R4 is not hydrogen; (iii) When R1-R10, Ar1, R', R", R11, and R12 are aryl, R1-R10, Ar1, R', R", R11, and R12 are substituted by group (a) chosen from D, halo, silane, boron, germanium, cyano, nitro, 1-20C alkylthio, 1-20C alkoxy, 1-20C alkyl, 2-20C alkenyl, 2-20C alkynyl, 6-20C aryl, deuterium-substituted 6-20C aryl, 2-20C heterocyclic group, 3-20C cycloalkyl, 7-20C arylalkyl, or 8-20C aryl alkenyl; (iv) When R1-R10, Ar1, R', R", R11 and R12 are fluorenyl, R1-R10, Ar1, R', R", R11 and R12 are substituted by D, halo, silane, cyano, 1-20C alkyl, 2-20C alkenyl, 6-20C aryl, deuterium-substituted 6-20C aryl, 2-20C heterocyclic group, or 3-20C cycloalkyl; (v) When R1-R10 are fused ring group, R1-R10 are substituted by group (a); (vi) When R1-R12 are alkyl, R1-R12 are optionally substituted by halo, silane, boron, cyano, 1-20C alkoxy, 1-20C alkyl, 2-20C alkenyl, 6-20C aryl, deuterium-substituted 6-20C aryl, 2-20C heterocyclic group, 7-20C arylalkyl, or 8-20C aryl alkenyl; (vii) When R1-R10 are alkenyl, R1-R10 are optionally substituted by group (a); and (viii) When R1-R10 are alkoxy or aryloxy, R1-R10 are substituted by D, halo, silane, 1-20C alkyl, 6-20C aryl, deuterium-substituted 6-20C aryl, 2-20C heterocyclic group, or 3-20C cycloalkyl.    SPECIFIC COMPOUNDS - 360 Carbazole derivatives e.g. 15,16,17,18-tetrahydrogenio-20-phenyl-10-thia-20-azapentacyclo(11.7.0.03,11.04,9.014,19)icosa-1,3(11),4,6,8,12,14(19),15,17-nonaene of formula (Ia), 17,20-diphenyl-10-thia-20-azapentacyclo(11.7.0.03,11.04,9.014,19)icosa-1,3(11),4,6,8,12,14(19),15,17-nonaene, 17-(naphthalen-1-yl)-20-phenyl-10-thia-20-azapentacyclo(11.7.0.03,11.04,9.014,19)icosa-1,3(11),4,6,8,12,14(19),15,17-nonaene, 17-(naphthalen-2-yl)-20-phenyl-10-thia-20-azapentacyclo(11.7.0.03,11.04,9.014,19)icosa-1,3(11),4,6,8,12,14(19),15,17-nonaene and 20-phenyl-16-(4-phenylphenyl)-10-thia-20-azapentacyclo(11.7.0.03,11.04,9.014,19)icosa-1,3(11),4,6,8,12,14(19),15,17-nonaene.