NOVELTY - A mixture contains a matrix material containing specified units; and a material which is capable of emission and which contains an element of atomic number above 20.    USE - In electronic parts, especially in organic light-emitting diodes (OLEDs), organic integrated circuits (O-ICs), organic field-effect-transistors (OFETs), organic thin-film-transistors (OTFTs), organic solar cells (O-SCs) or organic laser diodes (O-Lasers), the mixture being an emission layer of an OLED which is especially of the type without use of a separate hole-blocking layer directly bordering an electron transport layer or without use of a separate hole-blocking layer and a separate electron transport layer directly bordering an electron injection layer or the cathode.(claimed).    ADVANTAGE - The use of the combination results in increased efficiency and greatly increased life-times, thus allowing construction of electronic devices such as OLEDs with a simplified layer structure.    DETAILED DESCRIPTION - A mixture contains    (a) a matrix material containing units of formula C:Q where Q = a non-bonding electron pair comprising O, S, Se or N; and    (b) a material which is capable of emission and which contains an element of atomic number above 20.    An INDEPENDENT CLAIM is also included for novel aromatic or heteroaromatic compounds of formulae (10a)-(15).    Z = CR1 or N;    Y = N;    R1 - R3 which must be different from each other = (a) H, CN, optionally cyclic 1-40C alkyl, alkoxy or alkylamino optionally with one or more non-adjacent -CH2- groups replaced by -R4C=CR4-, -Ctriple bondC-, C=O, C=S, C=Se, C=NR4, -O-, -S-, -NR5- or -CONR6- and optionally with one or more H replaced by F, Cl, Br or I or (b) a 1-40C (hetero)aromatic system optionally with one or more H replaced by F, Cl, Br or I and optionally substituted by one or more non- aromatic residue R1 where one or more R1 and/or R1, R2 are on the same or different rings or stretch between a mono and poly-cyclic aliphatic or aromatic ring system; and    R4 - R6 = H or 1-20C aliphatic or aromatic hydrocarbon;    Ar = a 2- 40C (hetero)aromatic system optionally with one or more H replaced by F, Cl, Br or I and optionally substituted with one or more non-aromatic residue R1 as per (b) above;    n = 0 or 1;    E = C or N;    R7 = (a) 1-40C alkyl, alkoxy or alkylamino optionally with one or more non-adjacent -CH2- groups replaced by -R4C=CR4-, -C=C-, C=O, C=S, C=Se, C=NR4, -O-, -S-, -NR4- or -CONR4-; (b) an aromatic group optionally substituted by halogen, alkyl, -CF3, -OH, -SH, -S-alkyl, alkoxy, - NO2, -CN, -COOH, -COOAlkyl, -NH2, -Nalkyl, benzyl or benzoyl; or (c) a 2-40C large aromatic system optionally with one or more H replaced by F, Cl, Br or I and optionally substituted by one or more non-aromatic residue where several R1 can stretch to a further mono- or poly-cyclic aliphatic or aromatic ring system;    A1 - A3 = R8 or CO-R7 when X = C or a free electron pair when X = N;    R8 = (a) H, F, Cl, Br, I, CN, NO2, an optionally cyclic 1-40C alkyl optionally with one or more non-adjacent -CH2- groups replaced by -R4C=CR4-, -Cequivalent toC-, C=O, C=S, C=Se, C=NR4, -O-, -S-, -NR4- or -CONR4- and optionally with one or more H replaced by F, Cl, Br or I or (b) a 1-40C (hetero)aromatic system optionally with one or more H replaced by F, Cl, Br or I and optionally substituted by one or more non-aromatic residue R1 where one or more R1 and/or R1/R4 are on the same or different rings or stretch between mono and poly-cyclic aliphatic or aromatic ring system; and    with the provisos that for compound of formula (10a) only the following combinations hold : (i) when R7 = alkyl without an alpha-H atom then Z, E and A1 - A3 can any of the given definitions; (ii) when R7 = an aromatic group and at least1 Z = N or CR1 with R1 not = H then E and A1 - A3 can be any of the given definitions; (iii) when R7 = an aromatic group, all Z's = CH and at least E = N then A1 - A3 can any of the given definitions; (iv) when R7 = an aromatic group, all Z's = CH and all E's = C then at least one of A1 - A3 = R8 other than alkyl and the other two can be any of the given definitions; (v) when R7 = an aromatic group, all Z's = CH, all E's = C and both A1 and A2 are as per the definitions with one other than H then A3 = CO- R7; and (vi) when R7 = a large aromatic group such as fluorene, spirobifluorene or triarylamine then Z, E and A1 - A3 are as per the definitions.