| Abstract
| - The early events following photoexcitation of the nonplanar porphyrin 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (H2DPP) have been examined using transient absorption spectroscopy. These studieswere motivated by previous results indicating that photoinduced conformational changes underlie many ofthe perturbed photophysical properties of nonplanar porphyrins. It is shown here that H2DPP undergoesconformational/vibrational relaxation and equilibration in the 1(π,π*) excited state that takes ∼10 ps, andthat this process is not observed for the nominally planar 5,10,15,20-tetraphenylporphyrin system. The relaxationdynamics in H2DPP likely involve out-of-plane deformations of the porphyrin macrocycle and motions ofthe peripheral phenyl rings and solvent molecules. The light-induced behavior of H2DPP can thus be describedby the following sequence of events: photoexcitation produces the unrelaxed 1(π,π*) excited state that evolvesinto the relaxed 1(π,π*) excited state in ∼10 ps, followed by decay to the 3(π,π*) excited state plus theground state in ∼1 ns.
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