Ultrafast intersystem crossing in nickel porphyrins

TL;DR

This paper investigates ultrafast intersystem crossing in nickel porphyrins, revealing how non-equilibrium vibrational dynamics influence rapid relaxation processes relevant for photocatalysis and medical applications.

Contribution

It introduces a ligand-field model incorporating lattice vibrations to explain femtosecond-scale decay and demonstrates how time-dependent x-ray absorption can probe intermediate states.

Findings

Irreversible decay occurs within hundreds of femtoseconds.

Non-equilibrium vibrational energy redistribution is key to relaxation.

X-ray absorption reveals details of intermediate states.

Abstract

We study the relaxation dynamics and intersystem-crossing to the metastable state in laser-pumped tetra and hexa-coordinated nickel porphyrins. We use a ligand-field model which takes into account the crystal field created by the porphyrin ring and axial ligands. By accounting for the energy redistribution of the lattice vibrations of the metal-ligand stretch mode we get an irreversible decay within the order of the hundreds of femtoseconds timescale. We show how non-equilibrium time-dependent x-ray absorption atthe Ni K-edge measurements can elucidate the nature of the intermediate states involved in the decay. Understanding radiationless transitions in this system is of interest for their relevance in photocatalytic systems and photothermal sensitizers for cancer treatment.