Extremely Strong Near-IR Two-Photon Absorption in Conjugated Porphyrin Dimers:  Quantitative Description with Three-Essential-States Model

Abstract

Two-photon absorption spectra (2PA) of a series of conjugated dimers and the corresponding monomer were studied in the near-IR region. All of the dimers show very large peak cross section values, sigma(2) = (3-10) x 10(3) GM (1 GM = 1 x 10(-50) cm(4) s photon(-1)), which is several hundred times larger than that obtained for the corresponding monomer in the same region. We explain such dramatic cooperative enhancement by a combination of several factors, such as strong enhancement of the lowest one-photon Q-transition, better resonance conditions in the three-level system, dramatic enhancement of the excited-state singlet-singlet transition, and parallel arrangement of consecutive transitions in dimers, as compared to perpendicular arrangement in the monomer. We show that the absolute values of the 2PA cross section in these molecules are quantitatively described by a quantum-mechanical expression, derived for the three-level model. We also demonstrate the possibility of singlet oxygen generation upon one- and two-photon excitation of these dimers, which makes them particularly attractive for photodynamic therapy.

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

“…and P 2 C 2 -THS 26 shows that the TPA cross-sections are increased for all the ionic dimers, Table 2. This increase must be due to the terminal charged aryl groups, all of which are electron-acceptors.…”

“…5,000-25,000 GM) and straightforward synthesis. 20,26,27 We recently reported the design of a hydrophilic 95 porphyrin dimer with a very large TPA cross-section, P 2 C 2 -NMeI, Fig. 1.…”

Full Characterization of Vibrational Coherence in a Porphyrin Chromophore by Two-Dimensional Electronic Spectroscopy

“…[29][30] The chromophore consists of a zinc porphyrin ring with attached substituents necessary for high solubility of the molecule in nonpolar solvents. The substituents lower the molecular symmetry from D 4h to D 2h resulting in the splitting of the Q band into two in plane orthogonal transition dipole moments, the Q x and Q y absorption bands.…”

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

“…[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.…”