NOVELTY - Substituted carbocyclic compounds (A) are new.    USE - (A) are useful for emitting light, preferably as emitter in an optoelectronic device, preferably organic light-emitting diodes, light-emitting electrochemical cells, light-emitting diodes sensors (preferably outwardly shielded gas and vapor sensors), optical temperature sensors, organic solar cells, organic field effect transistors, organic lasers, organic diodes, organic photodiodes and down conversion systems (all claimed).    DETAILED DESCRIPTION - Substituted carbocyclic compounds (A) of formulae (Ia) and (Ib), are new. The donor D1 and acceptor A1 are connected via a single bond. The energy difference (S1-T1) between lowest excited singlet (S1) and underlying triplet (T1) state of the (A) is less than 1500 cm-1, preferably less than 200 cm-1.    D1 (donor) = aromatic or heteroaromatic group on which highest occupied molecular orbital is localized;    A1 (acceptor) = aromatic or heteroaromatic chemical group on which lowest unoccupied molecular orbital is localized;    Z1, Z2 = alkyl (-CnH2n+1), cycloalkyl (CmH2m-1), substituted alkyl, substituted cycloalkyl, alkoxy (-OCoH2o+1), thioalkoxy (-SCpH2p+1), alkylated amine (-N (CqH2q+1) (Cq'H2q'+1)) or (-N(CrH2r) (Cr'H2r'));    n = 1-4;    m = 3-6;    o, p = 1-4;    q, q' = 1, 2 or 3; and    r, r' = 5 or 6.    INDEPENDENT CLAIMS are also included for:    (1) an optoelectronic device, comprising (A); and    (2) selecting (A) with shorter inter-system crossingtime, comprising (a) providing (A), (b) determining lying localized excited states on the donor D1 and/or the acceptor A1 of (A), whether the localized states are closely adjacent to the charge transfer states of (A) using quantum mechanical method including time-dependent density functional theory or coupled-cluster method, where the energy distances should be less than 2000 cm-1, preferably less than 200 cm-1, provided that the localized excited states are in close proximity to the charge transfer state of the organic molecule, and alterating donor and/or acceptor strengths of the donor and/or acceptor fragments of the molecule and then repeating step (b) until (A) is selected with appropriately low energy intervals between the states.