Through space singlet-singlet and triplet-triplet ...
|Title||Through space singlet-singlet and triplet-triplet energy transfers in cofacial bisporphyrins held by the carbazoyl spacer.|
|Author(s)||C. Gros, S. Aly, M. El Ojaimi, J. Barbe, F. Brisach, A. Abd-El-Aziz, R. Guilard, P. Harvey|
|Journal||Section Title: Inorganic Chemicals and Reactions, Journal of Porphyrins and Phthalocyanines|
|Abstract||The through space singlet-singlet and triplet-triplet energy transfers in cofacial bis(etio-porphyrins) rigidly held by the carbazoyl spacer (3,6-bis(tert-butyl)-1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]carbazole, H4L), were studied. H4L and the complexes H2ZnL, Zn2L, H2PdL, Pd2L and ZnPdL were prepd. and their UV-visible absorption and luminescence data are presented. The studies on singlet-singlet transfer, which operates via a Forster mechanism, were performed using the zinc porphyrin and free base chromophores as energy donor and acceptor, resp., while the study on triplet-triplet processes was performed using the palladium porphyrin, and the zinc porphyrin and free base chromophores as donor and acceptors, resp. The rate for singlet-singlet transfer (kET(singlet)) is unexpectedly slower than that reported for other similar, rigidly held bisporphyrins such as H2(DPO)Zn (DPO = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzofuran) and H2(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 H2(DPX)Pd (DPX = 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene) and H2(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 Forster mechanism is inoperative for triplet-triplet processes). The kET(triplet) increases at 298 K which is tentatively interpreted by favorable excited state distortions in the triplet state and fluxion processes which ease intramol. transfers for these dyads in fluid soln. in comparison with former glassy matrixes. [on SciFinder(R)]|
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