NOVELTY - Copper(I) complexes (I) are new.    USE - (I) are useful as an emitter or absorber for converting UV-radiation or blue light into visible light, preferably into green, yellow or red light in optoelectronic components, preferably organic light-emitting components, light-emitting electrochemical cells, organic light-emitting diode-based sensors, preferably non-hermetically and outwardly shielded gas- and vapor sensors, organic solar cells, organic field effect transistors, organic lasers, down-conversion elements, organic diodes, organic transistors, organic light-emitting diodes, light-emitting electrochemical cells, and organic field-effect transistors (all claimed).    ADVANTAGE - (I) can be produced in a simple and cost-effective manner, comprises copper, which is cheap and less toxic, and exhibits high emission quantum yield (preferably greater than 50%).    DETAILED DESCRIPTION - Copper(I) complexes of formula (I) are new.    X = Cl, Br, I, CN, SCN, alkynyl and/or N3;    T1 = bidentate ligand of formula (N1T2E) (II) (optionally substituted by at least one group Z1);    E = phosphanyl or arsanyl group of type (R)2E;    R = alkyl, aryl, alkoxy, phenoxy or amide;    N1 = imine, which is a component of N-heteroaromatic 5-membered ring comprising pyrazole, isoxazole, isothiazole, triazole, oxadiazole, thiadiazole, tetrazole, oxatriazole or thiatriazole;    T2 = at least one C, which is component of aromatic group, where C is located directly adjacent to imine N and P or As; and    Z1 = group for increasing solubility of (I) in organic solvent.    INDEPENDENT CLAIMS are also included for:    (1) preparing (I);    (2) use of (I) as an emitter or absorber in an optoelectronic component;    (3) producing the optoelectronic component, comprising using (I);    (4) a bidentate ligand containing substituted heterocyclic compounds of formula (V)-(IX) for producing (I);    (5) preparing (V)-(IX), comprising reacting substituted heterocyclic compounds of formula (Va), (VIa), (VIIa), (VIIIa) and (IXa) with hydrocarbyl chloride compounds of formula (E1-(R1)2-Cl) and a base to obtain (V)-(IX); and    (6) modifying emission- and/or absorption properties of the electronic component, comprising introducing (I) into a matrix material for conducting electrons and holes in the optoelectronic component.    X1 = O, S or NR2; either    R1-R3 = hydrogen, halogen, or substituents on oxygen (-OR), nitrogen (-N(R)2), or silicon (-Si(R)3) which are attached to alkyl (branched or cyclic), aryl, heteroaryl, alkenyl, or substituted alkyl (branched or cyclic), aryl, heteroaryl and alkenyl which are substituted by e.g. halogens or deuterium, alkyl groups (or branched or cyclic), and donor or acceptor groups, such as amines, carboxylates and their esters, and CF3 groups; or    R2+R3 = ring; and    E1 = As or P.