Strong Two-Photon Absorption in New Asymmetrically Substituted Porphyrins:  Interference between Charge-Transfer and Intermediate-Resonance Pathways

Abstract

We study two-photon absorption (2PA) in two series of new free-base porphyrins with 4-(diphenylamino)stilbene or 4,4'-bis-(diphenylamino)stilbene (BDPAS) attached via pi-conjugating linkers at the porphyrin meso-position. We show that this new substitution modality increases the 2PA cross section in the Soret band region (excitation wavelength 750-900 nm) of the core porphyrin by nearly 2 orders of magnitude, from sigma(2) approximately 10 GM for the meso-phenyl-substituted analogue to sigma(2) approximately 10(3) GM for the ethynyl-linked BDPAS-porphyrin dyad. The 2PA properties are quantitatively described by considering two different and interfering 2PA quantum transition pathways. The first path involves virtual transition via intermediate one-photon resonance. The second path bypasses the intermediate resonance and occurs due to a large permanent dipole moment difference between the ground and the final electronic states. To our best knowledge, this is the first experimental observation of the combined effect of these two pathways on one particular two-photon transition, resulting in quantum-interference-modulated 2PA strength.

Photophysical properties and intracellular imaging of water-soluble porphyrin dimers for two-photon excited photodynamic therapy

“…41 The TPA cross-sections of this series of conjugated porphyrin 235 dimers compare favourably with the values of other potential photosensitisers designed for two-photon excited PDT. For example, TPA cross-sections of ca 2000 GM have been reported for tetraphenyl-porphycenes (determined via two-photon excited singlet oxygen detection), 18 ca 1000 GM for porphyrin-TPA chromophore 240 assemblies (determined via two-photon excited fluorescence, similar to the present work) 19 and 7900 GM for self-assembled porphyrin dimers (determined by the z-scan technique). 24 The high TPA efficiencies of our porphyrin dimers within the 'therapeutic window' of biological tissues (700-950 nm) 4 in 245 combination with the high singlet oxygen quantum yields highlight these compounds as promising photosensitisers for two-photon excited PDT.…”

One- and two-photon activated phototoxicity of conjugated porphyrin dimers with high two-photon absorption cross sections

“…Photodynamic therapy (PDT) uses a light-activated drug, 25 known as a photosensitiser, to treat neoplastic diseases. [1][2][3][4][5][6][7][8] The treatment is relatively benign and gives good cosmetic outcomes.…”

“…[22][23][24][25][26] Recently, focus has turned to compounds for two-photon excited PDT, although only a few of these have shown in vitro activity and few in vivo studies have been published. 27-33 60 We have recently reported a family of ionic conjugated porphyrin dimers with peak TPA cross-sections as large as 17,000 GM (Fig.…”

Carrier-envelope phase-dependent transmitted spectra in inversion-asymmetric media with permanent dipole moments

“…Previous investigations have demonstrated that the twophoton transition in the long pulse case can be greatly enhanced due to the presence of the PDM in the medium [32,33]. As a result, the medium initially absorbs energy from the pulse by two-photon transition, and then reemits it back at the resonant frequency of the medium (ω 0 = 2ω p ).…”