Octopolar D2-symmetric chromophores,
based on the MPZnM supermolecular motif in which (porphinato)zinc(II)
(PZn) and ruthenium(II) polypyridyl (M) structural units are connected
via ethyne linkages, were synthesized. These structures take advantage
of electron-rich meso-arylporphyrin or electron-poor meso-(perfluoroalkyl)porphyrin macrocycles, unsubstituted
terpyridyl and 4′-pyrrolidinyl-2,2′;6′,2″-terpyridyl
ligands, and modulation of metal(II) polypyridyl-to-(porphinato)zinc
connectivity, to probe how electronic and geometric factors impact
the measured hyperpolarizability. Transient absorption spectra obtained
at early time delays (tdelay < 400
fs) demonstrate fast excited-state relaxation, and formation of a
highly polarized T1 excited state; the T1 states
of these chromophores display expansive, intense T1 →
Tn absorption manifolds that dominate
the 800–1200 nm region of the NIR, long (μs) triplet-state
lifetimes, and unusually large NIR excited absorptive extinction coefficients
[ε(T1 → Tn) ∼
105 M–1 cm–1]. Dynamic
hyperpolarizability (βλ) values were determined
from hyper-Rayleigh light scattering (HRS) measurements, carried out
at multiple incident irradiation wavelengths spanning the 800–1500
nm spectral domain. The measured βHRS value (4600
± 1200 × 10–30 esu) for one of these complexes,
RuPZnRu, is the largest yet reported for any chromophore at a 1500
nm irradiation wavelength, highlighting that appropriate engineering
of strong electronic coupling between multiple charge-transfer oscillators
provides a critical design strategy to realize octopolar NLO chromophores
exhibiting large βHRS values at telecom-relevant
wavelengths. Generalized Thomas–Kuhn sum (TKS) rules were utilized
to compute the effective excited-state-to-excited-state transition
dipole moments from experimental linear-absorption spectra; these
data were then utilized to compute hyperpolarizabilities as a function
of frequency, that include two- and three-state contributions for
both βzzz and βxzx tensor components to the RuPZnRu hyperpolarizability
spectrum. This analysis predicts that the βzzz and βxzx tensor contributions
to the RuPZnRu hyperpolarizability spectrum maximize near 1550 nm,
in agreement with experimental data. The TKS analysis suggests that
relative to analogous dipolar chromophores, octopolar supermolecules
will be likely characterized by more intricate dependences of the
measured hyperpolarizability upon irradiation wavelength due to the
interactions among multiple different β tensor components.