Abstract
The effects of Mg, Zn, Cd, and Pd dications on the photophysical properties of the tetraphenylporphyrin ligand have been explored, considering the corresponding complexes and by using the density functional theory and its time-dependent extension. Results show that absorption wavelengths do not change significantly when the metal ion changes contrary to what happens to the singlet–triplet energy gaps (ΔES−T) and the spin-orbit matrix elements . The most probable intersystem spin crossing (ISC) pathways for the population of the lowest triplet states have been explored. Our findings can contribute to rationalize the available experimental data and promote the potential therapeutic use of these compounds as photosensitizers in photodynamic therapy (PDT).
Highlights
The transitions between pure spin states of different multiplicities are, as it is well known, forbidden by the spin selection rules
It is known that these transitions can occur as result of a spin–orbit coupling (SOC), a relativistic effect that induces a quantum mechanical mixing between states with different spin multiplicity
Ground and excited state optimizations have been performed by using M06 [40] exchange correlation functional coupled with the all electron 6-31G* basis sets for all the atoms except for Cd correlation functional coupled with the all electron 6-31G* basis sets for all the atoms except for Cd and Pd, for which the SSD pseudopotential has been employed for DFT and TDDFT levels of theory
Summary
The transitions between pure spin states of different multiplicities are, as it is well known, forbidden by the spin selection rules. Several spin-forbidden intersystem crossings in organic and inorganic systems are reported to be essential for a specific action in different areas [1,2,3]. It is known that these transitions can occur as result of a spin–orbit coupling (SOC), a relativistic effect that induces a quantum mechanical mixing between states with different spin multiplicity. Since the nuclear magnetic field depends on nuclear charge, the SOCs assume greater values with the increasing of the atomic number. Based on what has been said before, the intersystem crossing (ISC) is observed often in systems containing high atomic number elements. The phenomenon is, known as heavy atom effect (HAE)
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