The invention relates to neutral mononuclear copper (I) complexes for emitting light and with a structure according to formula (A) in which: M represents: Cu(I); L∩L represents: a single, negatively charged, bidentate ligand; N∩N represents: a diimine ligand (substituted with R and FG), in particular a substituted 2,2′-bipyridine derivative (bpy) or a substituted 1,10-phenanthroline derivative (phen); R represents: at least one sterically demanding substituent for preventing the planarization of the complex in the excited state; FG=functional group, and represents: at least one second substituent for increasing solubility in organic solvents. The substituent can also be used for electron transport or alternatively for hole transport, said functional group being bound to the diimine ligands either directly or by means of suitable bridges; and the copper (I) complex: having a ΔE(S1−T1) value of less than 2500 cm−1 between the lowest excited singlet state (S1) and the triplet state (T1) which lies below; having an emission lifespan of at most 20 μs; having an emission quantum yield of greater than 40%, and a solubility of at least 1 g/L in organic solvents, in particular polar organic hydrocarbons such as acetone, methyl ethyl ketone, benzene, toluene, chlorobenzene, dichlorobenzene, dichloromethane, chloroform, dichloroethane, tetrachloroethylene, alcohols, acetonitrile or water.