Hs. Eom et al., ULTRAFAST VIBRATIONAL-RELAXATION AND LIGAND PHOTODISSOCIATION PHOTOASSOCIATION PROCESSES OF NICKEL(II) PORPHYRINS IN THE CONDENSED-PHASE/, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 101(20), 1997, pp. 3661-3669
We have carried out a femtosecond transient absorption spectroscopic s
tudy on nickel(II) porphyrins in various solvents in order to obtain d
etailed information on vibrational relaxation processes occurring in t
he initial stage after photoexcitation to the highly excited states. W
e found the decay process of time constant of approximately 1 ps corre
sponding to the intramolecular vibrational relaxation process for Ni(I
I)TPP and Ni(II)OEP in toluene. In addition to this process, the inter
molecular vibrational relaxation process with 10-20 ps lifetime was al
so observed for Ni(II)OEP in toluene, although its contribution to the
overall decay process is relatively weak probably due to the weak sol
ute/solvent interaction. In coordinating solvents such as pyridine and
piperidine, we observed the intramolecular vibrational relaxation pro
cesses before complete population of the bottleneck excited metal (1)\
0,d(z2)] or (3)\0,(3)(d,d)]. In this case, it is likely that the inter
molecular vibrational relaxation process associated with photodissocia
tion/photoassociation processes depending on the selective excitation
of four- and six-coordinate species is accompanied by the intramolecul
ar vibrational relaxation due to the strong solute/solvent interaction
. These processes are also believed to be responsible for the excess e
nergy dissipation of highly excited nickel(II) porphyrins into the sur
rounding solvent molecules.