  Photoexcited organic chromophores appended to molecular qubits can serve as a
source of spin initialization or multi-level qudit generation for quantum
information applications. So far, this approach has been primarily investigated
in chromophore/stable radical systems. Here, we extend this concept to a
meso-meso linked oxovanadium(IV) porphyrin - free base porphyrin dimer.
Femtosecond transient absorption experiments reveal that photoexcitation of the
free base porphyrin leads to picosecond triplet state formation via enhanced
intersystem crossing. Time-resolved electron paramagnetic resonance (TREPR)
experiments carried out at both 85 K and room temperature reveal the formation
of a long-lived spin-polarized quartet state through triplet-doublet spin
mixing. Notably, a distinct hyperfine structure arising from the interaction
between the electron spin quartet state and the vanadyl nucleus (51V, I=7/2) is
evident, with the quartet state exhibiting long-lived spin polarization even at
room temperature. Theoretical simulations of the TREPR spectra confirm the
photogenerated quartet state and provide insights into the non-Boltzmann spin
populations. Exploit-ing this phenomenon affords the possibility of using
photoinduced triplet states in porphyrins for quantum information as a resource
to polarize and magnetically couple molecular electronic or nuclear spin qubits
and qudits.
