Two-Photon Photosensitized Production of Singlet Oxygen:  Optical and Optoacoustic Characterization of Absolute Two-Photon Absorption Cross Sections for Standard Sensitizers in Different Solvents

Abstract

Singlet molecular oxygen, O2(a1Deltag), can be produced upon resonant two-photon excitation of a photosensitizer. In the present study, two molecules that have received recent attention in studies of nonlinear organic materials were characterized for use as standard two-photon sensitizers: 2,5-dicyano-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene, CNPhVB, and 2,5-dibromo-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene, BrPhVB. Absolute two-photon absorption cross sections, delta, were independently determined for these molecules using two techniques that have heretofore not been applied to this problem: an optical technique (time-resolved detection of O2(a1Deltag) phosphorescence) and a nonoptical technique (a time-resolved laser-induced optoacoustic experiment). For experiments performed in toluene, a solvent commonly used for such nonlinear optical studies, appreciable absorption by the solvent itself complicates the measurements. In cyclohexane, however, delta values could be obtained without the interfering effects of solvent absorption. On the basis of these results, we discuss key aspects of the respective techniques used to quantify values of delta. The information reported herein provides some explanation for the lack of consensus that is routinely observed in published values of delta, certainly for experiments performed in aromatic solvents such as toluene and benzene.

Direct 765 nm Optical Excitation of Molecular Oxygen in Solution and in Single Mammalian Cells

“…33,45 Briefly, for the studies in bulk solvents, the amplified output of a Ti:Sapphire laser was used to pump an optical parametric amplifier at a 1 kHz repetition rate yielding pulses tunable over a large wavelength 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 21 range. 45 The cell studies were performed using a different tunable Ti:Sapphire system operated at 80 MHz. 33 The output of this laser was coupled through the objective of an inverted microscope to facilitate irradiation with subcellular spatial resolution.…”

New Two-Photon Activated Photodynamic Therapy Sensitizers Induce Xenograft Tumor Regressions after Near-IR Laser Treatment through the Body of the Host Mouse

“…Because the intrinsic 2PA cross-sections of readily available sensitizers is very low, r 2 < 10 to 100 Goeppert-Mayer units (where 1 Goeppert-Mayer unit = 10 -50 cm 4 s photon -1 ; ref. 12), there have been continuous efforts toward synthesizing new sensitizers with increased 2PA efficiency, including FRET dendrimers (13) and decorated nanoparticles (14). Recent in vitro studies with two-photon activation of Photofrin show killing of vascular endothelial cells but still require high-pulse energy and long illumination times (15).…”

“Dark” Excited States of Diphenylacetylene Studied by Nonresonant Two-Photon Excitation Optical-Probing Photoacoustic Spectroscopy

“…According to our experimental results, the two-photon excitation spectrum obtained by the OPPAS measurement results from the structure belonging to the D 2h point group, and the two-photon allowed 2 1 A g and 1 1 B 3g states were above one-photon allowed 1 1 B 1u state. Two-photon absorption cross section can be obtained by photothermal techniques since they are calorimetric in essence [30,31]. The estimation of the cross section of DPA is in progress.…”

“…With a photothermal technique, the two-photon absorption was reported [30,31]. For nonfluorescent molecules like DPA, the calorimetric techniques are very useful.…”