One- and two-photon absorption of highly conjugated multiporphyrin systems in the two-photon Soret transition region

Abstract

This study presents a detailed investigation of near-infrared one-and two-photon absorption ͑TPA͒ in a series of highly conjugated ͑porphinato͒zinc͑II͒ compounds. The chromophores interrogated include meso-to-meso ethyne-bridged ͑porphinato͒zinc͑II͒ oligomers ͑PZn n species͒, ͑porphinato͒zinc͑II͒-spacer-͑porphinato͒zinc͑II͒ ͑PZn-Sp-PZn͒ complexes, PZn n structures featuring terminal electron-releasing and -withdrawing substituents, related conjugated arrays in which electron-rich and -poor PZn units alternate, and benchmark PZn monomers. Broadband TPA cross-section measurements were performed ratiometrically using fluorescein as a reference. Superficially, the measurements indicate very large TPA cross-sections ͑up to ϳ10 4 GM; 1 GM =1ϫ 10 −50 cm 4 s photon −1 ͒ in the two-photon Soret ͑or B-band͒ resonance region. However, a more careful analysis of fluorescence as a function of incident photon flux suggests that significant one-photon absorption is present in the same spectral region for all compounds in the series. TPA cross-sections are extracted for the first time for some of these compounds using a model that includes both one-photon absorption and TPA contributions. Resultant TPA cross-sections are ϳ10 GM. The findings suggest that large TPA cross-sections reported in the Soret resonance region of similar compounds might contain significant contributions from one-photon absorption processes.

Amplified Two‐Photon Absorption in Trans‐A2B2‐Porphyrins Bearing Nitrophenylethynyl Substituents

“…Therien and co-workers studied two-photon absorption of very similar p-extended porphyrins claiming that 2PA cross-sections are on the order of 10 GM, and that a significant portion of the detected fluorescence is the result of other, linear ab-sorptive processes. [19] However, direct comparison of these results is not justified in this case, because these authors used very different experimental conditions from ours. Their laser has high repetition rate (100 MHz) and low peak power (~1 nJ per laser pulse) whereas we used low-repetition-rate (1 kHz) / high-peak-power (> 5 mJ) pulses.…”

“…[19] However, direct comparison of these results is not justified in this case, because these authors used very different experimental conditions from ours. Their laser has high repetition rate (100 MHz) and low peak power (~1 nJ per laser pulse) whereas we used low-repetition-rate (1 kHz) / high-peak-power (>5 µJ) pulses.…”

Remarkable two-photon absorption in open-shell singlet systems

“…Although it has been already used as a powerful tool in spectroscopy and quantum optics, 1-4 in the last decade, its applications have been extended to new nanotechnologies in the fields of chemistry, biology, and photonics [5][6][7][8] and attracted enlarged experimental and theoretical interests, particularly, for molecular systems. Several proposals for designing molecular structures with large TPA cross sections have been presented, e.g., the symmetric/asymmetric introduction of donor ͑D͒/acceptor ͑A͒ groups at the ends/centers of -conjugated systems such as D − −A− −D and D− −A, [10][11][12][13][14][15][16][17][18][19] the extension of -conjugation in porphyrin derivatives, [20][21][22][23][24][25][26] as well as exciton coupling in multibranched chromophores. 27 Moreover, owing to the common third-order NLO character, some of these strategies for controlling TPA present similarities to the design of nonresonant NLO responses.…”

The effect of the structure and conformational dynamics on quenching of triplet states of porphyrins and their chemical dimers by molecular oxygen and on singlet oxygen generation

“…The study of dimeric and oligomeric porphyrins is also of interest from the viewpoint of the possibility of changing the structure and the aggregation, redox, spectral, and photophysical properties of monomeric porphyrins by changing the degree of coupling of their π conjugated systems [10][11][12][13][14]. It is known, for exam ple, that dimerization of porphyrins in most cases leads to a noticeable bathochromic shift of the long wavelength absorption band, which can be used for development of sensitizers for photodynamic therapy (PDT) of oncological diseases since they have intense absorption in the transparency range of biological tis sues.…”