ENERGY TRANSFER-ENHANCED CHEMILUMINESCENCE OF ADAMANTANONE (N,PI-ASTERISK) AND ESTER (PI,PI-ASTERISK) SINGLET AND TRIPLET EXCITED-STATES INTHE THERMOLYSIS OF SILYLOXYARYL-SUBSTITUTED SPIROADAMANTYL DIOXETANES

The thermal generation of singlet and triplet excited states from sily oxyaryl-substituted spiroadamantyl dioxetanes 1a,b and the adamantylid ineadamantane dioxetane (1c) was investigated by direct and enhanced c hemiluminescence (CL). 9,10-Diphenylanthracene (DPA) and 9-fluorenone were used as energy accepters in the singlet-singlet (S-S), naphthalen e and europium chelate Eu(TTA)(3)Phen (TTA = thenoyltrifluoroacetone, Phen = 1,10-phenanthroline) in the triplet-triplet (T-T) and 9,10-dibr omoanthracene (DBA) in tripler-singlet (T-S) energy transfer experimen ts. The direct chemiluminescence observed in the thermolysis of dioxet anes 1a,b consisted of fluorescence derived from the singlet-excited a damantanones 2a,b. In the presence of naphthalene, selective T-S energ y transfer with DBA (napthalene as quencher) displayed the adamantanon e triplets 2a,b and with Eu(TTA)(3)Phen (naphthalene as mediator) also the silyloxyaryl ester 3 triplets. From the Stern-Volmer constants (k (TN tau T)(0)) the triplet lifetimes tau(T)(0) of these triplet state products were assessed. By using the Hastings-Weber standard, the tota l triplet excitation yield (Phi(T)) was estimated to be ca 20%. The en ergies of the first excited singlet and triplet states of the adamanta nones 2a,b and the silyloxyaryl ester 3, the products of the thermally induced decomposition of dioxetanes 1a-c, were determined by semiempi rical calculations (AM1-based configuration interaction), which includ ed explicitly solvent effects on the excitation energies in terms of a self-consistent reaction field approach. The calculations revealed th at the first excited singlet and tripler states of the adamantanones 2 a,b are expectedly n,pi-type excitations while the silyloxyaryl eater 3 possesses pi,pi character. The semiempirical computations suggest that excitation of the adamantanones 2a,b as well as the silyloxyaryl ester 3 is feasible in the thermolysis of the spiroadamantyl dioxetane s 1a,b, which has been confirmed by the experimental energy transfer s tudies.