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Triplet–Triplet Energy Transfer Controlled by the Donor–Acceptor Distance in Rigidly Held Palladium‐Containing Cofacial Bisporphyrins
Author(s) -
Faure Sébastien,
Stern Christine,
Espinosa Enrique,
Douville Jasmin,
Guilard Roger,
Harvey Pierre D.
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400990
Subject(s) - chemistry , biphenylene , palladium , acceptor , crystallography , stereochemistry , medicinal chemistry , catalysis , physics , organic chemistry , polymer , phenylene , condensed matter physics
Eleven new complexes, including mono‐, heterobi‐, and homobimetallic cofacial bisporphyrins, (Pd)H 2 DPS, (M)H 2 DPX, (M)H 2 DPB, (PdZn)DPS, (PdZn)DPX, (Pt) 2 DPX, (M) 2 DPB (M=Pd, Pt), and (Pt)P (DPS 4− =4,6‐bis[5‐(2,8,13,17‐tetraethyl‐3,7,12,18‐tetramethylporphyrinyl)]dibenzothiophene tetraanion, DPX 4− =4,5‐bis[5‐(2,8,13,17‐tetraethyl‐3,7,12,18‐tetramethylporphyrinyl)]‐9,9‐dimethylxanthene tetraanion, DPB 4− =1,8‐bis[5‐(2,8,13,17‐tetraethyl‐3,7,12,18‐tetramethylporphyrinyl)]biphenylene tetraanion, P 2− =5‐phenyl‐2,8,13,17‐tetraethyl‐3,7,12,18‐tetramethylporphyrin dianion) have been synthesized and characterized. The photophysical properties of the donor (M) P (M=Pd or Pt, P =porphyrin chromophore) and the acceptor (free base H 2 P or (Zn) P ) depend on the C meso –C meso distance and the presence of a heavy atom such as Pd II or Pt II . The data were compared with those for the known compounds (Pd) 2 DPS, (Pd) 2 DPX, H 4 DPS, H 4 DPX, H 4 DPB, (Pd) P , (Zn) P , and H 2 P . The rate constants for triplet–triplet energy transfer ( k ET ) were measured for the heterobimetallic (PdZn) and monometallic [(M)H 2 ] derivatives (M=Pd, Pt). The fluorescence lifetimes (Δ τ F ) of the acceptors decrease as a result of the heavy‐atom effect, and vary as follows: (Pd)H 2 DPS≪(Pd)H 2 DPX∼(Pd)H 2 DPB. The k ET values calculated according to the equation k ET =(1/ τ emi −1/ τ emi 0 ), where τ emi 0 is the emission lifetime of the homobimetallic bisporphyrins (no ET occurs), are equal to 0, 247±57 and 133±52 s −1 for DPS, DPX, and DPB, respectively, in the (Pd)H 2 series. These measurements allowed the range of distance over which the Dexter mechanism for T 1 –T 1 energy transfer ceases to operate to be determined. This distance is somewhere between 4.3 and 6.3 Å, in agreement with our recent findings on singlet–singlet energy transfer. During the course of this study, the X‐ray crystal structure for (Pd)H 2 DPX was obtained; triclinic ( P $\bar 1$ ), a =11.1016(1), b =14.9868(2), c =20.6786(3) Å, α =102.091(1), β =100.587(1), γ =101.817(1)°, V =3199.19(7) Å 3 , Z =2.