6533b820fe1ef96bd12791bf

RESEARCH PRODUCT

Through space singlet-singlet and triplet-triplet energy transfers in cofacial bisporphyrins held by the carbazoyl spacer

Shawkat Mohammed AlyFrédéric BrisachClaude P. GrosAlaa S. Abd-el-azizJean-michel BarbeMaya El OjaimiPierre D. HarveyRoger Guilard

subject

energy transfer010405 organic chemistryFree baseGeneral ChemistryBiphenylene010402 general chemistryPhotochemistrypalladium01 natural sciences7. Clean energyPorphyrin0104 chemical sciences[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistrychemistry.chemical_compoundchemistryExcited state[ CHIM.THEO ] Chemical Sciences/Theoretical and/or physical chemistryFlash photolysisface to face bisporphyrinsSinglet stateTriplet statePhosphorescenceComputingMilieux_MISCELLANEOUS

description

The through space singlet-singlet and triplet-triplet energy transfers in cofacial bis(etio-porphyrins) rigidly held by the carbazoyl spacer were investigated. The studies on singlet-singlet transfer, which operates via a Förster mechanism, were performed using the zinc porphyrin and free base chromophores as energy donor and acceptor, respectively, while the investigation on triplet-triplet processes was performed using the palladium porphyrin, and the zinc porphyrin and free base chromophores as donor and acceptors, respectively. The rate for singlet-singlet transfer ( k ET ( singlet )) is unexpectedly slower than that reported for other similar, rigidly held bisporphyrins such as H 2( DPO ) Zn ( DPO = 4,6- bis [5-(2,8,13,17- tetraethyl -3,7,12,18- tetramethylporphyrinyl )] dibenzofuran ) and H 2( DPS ) Zn ( DPS = 4,6- bis [5-(2,8,13,17- tetraethyl -3,7,12,18- tetramethyl - porphyrinyl )] dibenzothiophene )). This slower rate is interpreted by the presence of the H -atom exactly located between the two meso-carbons in the dyads. The rates for triplet-triplet transfer are also slow but not too different from that recently reported for H 2( DPX ) Pd ( DPX = 4,5- bis [5-(2,8,13,17- tetraethyl -3,7,12,18- tetramethylporphyrinyl )]-9,9- dimethylxanthene ) and H 2( DPB ) Pd ( DPB = 1,8- bis [5-(2,8,13,17- tetraethyl -3,7,12,18- tetramethylporphyrinyl )] biphenylene ) at 77 K. In such cases, the slow rate is interpreted by a through space energy transfer pathway which operates according to a (small range) Dexter mechanism (since the Förster mechanism is inoperative for triplet-triplet processes). The k ET (triplet) increases at 298 K which is tentatively interpreted by favorable excited state distortions in the triplet state and fluxion processes which ease intramolecular transfers for these dyads in fluid solution in comparison with former glassy matrices.

https://hal.archives-ouvertes.fr/hal-00458496