TY - JOUR

T1 - Giant magnetic field effects in donor-acceptor triads

T2 - On the charge separation and recombination dynamics in triarylamine-naphthalenediimide triads with bis-diyprrinato-palladium(II), porphodimethenato-palladium(II), and palladium(II)-porphyrin photosensitizers

AU - Riese, Stefan

AU - Brand, Jessica S.

AU - Mims, David

AU - Holzapfel, Marco

AU - Lukzen, Nikita N.

AU - Steiner, Ulrich E.

AU - Lambert, Christoph

PY - 2020/8/7

Y1 - 2020/8/7

N2 - A series of triads consisting of a triarylamine donor, a naphthalenediimide acceptor, and a palladium photosensitizer bridge was investigated for the photoinduced electron transfer processes and the spin chemistry involved. In this series, the ligand in the palladium photosensitizer was varied from bis-dipyrrinato to porphodimethenato and to a porphyrin. With the porphyrin photosensitizer, no charge separated state could be reached. This is caused by the direct relaxation of the excited photosensitizer to the ground state by intersystem crossing. The bis-dipyrrinato-palladium photosensitizer gave only a little yield (7%) of the charge separated state, which is due to the population of a metal centered triplet state and a concomitant geometrical rearrangement to a disphenoidal coordination sphere. This state relaxes rapidly to the ground state. In contrast, in the porphodimethenato-palladium triads, a long lived (μs to ms) charge separated state could be generated in high quantum yields (66%-74%) because, here, the population of a triplet metal centered state is inhibited by geometrical constraints. The magnetic field dependent transient absorption measurement of one of the porphodimethenato triads revealed a giant magnetic field effect by a factor of 26 on the signal amplitude of the charge separated state. This is the consequence of a magnetic field dependent triplet-singlet interconversion that inhibits the fast decay of the charge separated triplet state through the singlet recombination channel. A systematic comparative analysis of the spin-dependent kinetics in terms of three classical and one fully quantum theoretical methods is provided, shedding light on the pros and cons of each of them.

AB - A series of triads consisting of a triarylamine donor, a naphthalenediimide acceptor, and a palladium photosensitizer bridge was investigated for the photoinduced electron transfer processes and the spin chemistry involved. In this series, the ligand in the palladium photosensitizer was varied from bis-dipyrrinato to porphodimethenato and to a porphyrin. With the porphyrin photosensitizer, no charge separated state could be reached. This is caused by the direct relaxation of the excited photosensitizer to the ground state by intersystem crossing. The bis-dipyrrinato-palladium photosensitizer gave only a little yield (7%) of the charge separated state, which is due to the population of a metal centered triplet state and a concomitant geometrical rearrangement to a disphenoidal coordination sphere. This state relaxes rapidly to the ground state. In contrast, in the porphodimethenato-palladium triads, a long lived (μs to ms) charge separated state could be generated in high quantum yields (66%-74%) because, here, the population of a triplet metal centered state is inhibited by geometrical constraints. The magnetic field dependent transient absorption measurement of one of the porphodimethenato triads revealed a giant magnetic field effect by a factor of 26 on the signal amplitude of the charge separated state. This is the consequence of a magnetic field dependent triplet-singlet interconversion that inhibits the fast decay of the charge separated triplet state through the singlet recombination channel. A systematic comparative analysis of the spin-dependent kinetics in terms of three classical and one fully quantum theoretical methods is provided, shedding light on the pros and cons of each of them.

KW - PHOTOINDUCED ELECTRON-TRANSFER

KW - RADICAL RECOMBINATION

KW - STATES

KW - PAIR

KW - RELAXATION

KW - COMPLEXES

KW - PHOTOCHEMISTRY

KW - SPECTROSCOPY

KW - PALLADIUM

KW - COHERENT

UR - http://www.scopus.com/inward/record.url?scp=85089261833&partnerID=8YFLogxK

U2 - 10.1063/5.0013941

DO - 10.1063/5.0013941

M3 - Article

C2 - 32770922

AN - SCOPUS:85089261833

VL - 153

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 5

M1 - 054306

ER -