Stabilizing g-States in Centrosymmetric Tetrapyrroles: Two-Photon-Absorbing Porphyrins with Bright Phosphorescence

Abstract

Using time-dependent density functional theory (TDDFT) and sum-overstates (SOS) formalism, we predicted significant stabilization of 2P-active g-states in a compact fully symmetric porphyrin, in which all four pyrrolic fragments are fused with phathalimide residues via the β-carbon positions. The synthesis of a soluble, nonaggregating meso-unsubstituted tetraarylphthalimidoporphyrin (TAPIP) was then developed, and the spectroscopic measurements confirmed that a strongly 2P-active state in this porphyrin is stabilized below the B (Soret) state level. Single-crystal X-ray analysis revealed near-ideally planar geometry of the TAPIP macrocycle, while its tetra-meso-arylated analogue (meso-ArTAPIP) was found to be highly saddled. Consistent with these structural features, Pt meso-ArTAPIP phosphoresces rather weakly (ϕ = 0.05 in DMF at 22 °C), while both Pt and Pd complexes of TAPIP are highly phosphorescent (ϕ = 0.45 and 0.23, respectively). In addition PdTAPIP exhibits non-negligible thermally activated (E-type) delayed fluorescence (ϕ(d) ∼ 0.012). Taken together, these photophysical properties make metal complexes of meso-unsubstituted tetaarylphthalimidoporphyrins the brightest 2P-absorbing phosphorescent chromophores known to date.

New red-emitting Schiff base chelates: promising dyes for sensing and imaging of temperature and oxygen via phosphorescence decay time

“…Suitability for multi-photon excitation is of particular interest since despite the large number of multi-photon emitters reported in the last few years58,59 rather few analyte-sensitive probes suitable for this method have been reported. For example, several probes for two-photon (2-P) imaging of oxygen distribution have been reported by Vinogradov and co-workers60–62 but a rather sophisticated design is important to achieve high multi-photon excitability. The new Pt( ii ) chelate may represent a simple alternative to these systems due to the push–pull character favouring 2-P absorption.…”

More homogeneous capillary flow and oxygenation in deeper cortical layers correlate with increased oxygen extraction

“…A new two-photon-excitable phosphorescence oxygen probe – Oxyphor2P was used in this study. Oxyphor2P belongs to the class of dendritically protected oxygen probes (Lebedev et al, 2009), and it is built around a newly developed Pt tetraarylphthalimidoporphyrin (PtTAPIP) (Esipova et al, 2017). In comparison to its predecessor (PtP-C343) (Finikova et al, 2008), Oxyphor2P exhibits red-shifted two-photon excitation and emission maxima, higher phosphorescence quantum yield and larger two-photon absorption cross-section (Esipova et al, 2019).…”

“…These improvements of Oxyphor2P facilitated large-scale sampling of both capillary RBC flow and PO 2 deeper in the brain, for example, 600 µm vs. 450 µm (Lyons et al, 2016; Sakadžić et al, 2014), and with higher signal-to-noise ratios, which, in turn, powered the statistical analyses beyond what could be achievable with PtP-C343 (Devor et al, 2011; Lecoq et al, 2011; Lyons et al, 2016; Parpaleix et al, 2013; Sakadzić et al, 2010; Sakadžić et al, 2014). In addition, the very high phosphorescence quantum yield of Oxyphor2P (Esipova et al, 2017; Esipova et al, 2019) enabled detection of RBC-passages in capillaries based on phosphorescence alone, without the need to enhance the signal from the blood plasma using additional chromophores (Lyons et al, 2016).…”

Cerebral tissue pO2 response to stimulation is preserved with age in awake mice

“…To reach a high temporal resolution as a requirement accurate measurement of tissue pO 2 response, we had to measure limited number of sampling points which does not allow the spatial identification of sparse hypoxic pockets. With the development of brighter pO 2 probes [42] which allow faster measurements, future studies may be able to investigate the hypoxia potential during stimulation in aged animals. One other limitation of the present study is that the OCT data (Fig.…”