Two-photon absorption has important advantages over conventional one-photon absorption, which has led to applications in microscopy, microfabrication, three-dimensional data storage, optical power limiting, up-converted lasing, photodynamic therapy, and for the localized release of bio-active species. These applications have generated a demand for new dyes with high two-photon absorption cross-sections. This Review introduces the theory of two-photon absorption, surveys the wide range of potential applications, and highlights emerging structure-property correlations that can serve as guidelines for the development of efficient two-photon dyes.

Two-photon absorption and the design of two-photon dyes.

Nature has chosen chlorophylls in plants as antennae to harvest light for the conversion of solar energy in complicated photosynthetic processes. Inspired by natural photosynthesis, scientists utilized artificial chlorophylls – the porphyrins – as efficient centres to harvest light for solar cells sensitized with a porphyrin (PSSC). After the first example appeared in 1993 of a porphyrin of type copper chlorophyll as a photosensitizer for PSSC that achieved a power conversion efficiency of 2.6%, no significant advance of PSSC was reported until 2005; beta-linked zinc porphyrins were then reported to show promising device performances with a benchmark efficiency of 7.1% reported in 2007. Meso-linked zinc porphyrin sensitizers in the first series with a push–pull framework appeared in 2009; the best cell performed comparably to that of a N3-based device, and a benchmark 11% was reported for a porphyrin sensitizer of this type in 2010. With a structural design involving long alkoxyl chains to envelop the porphyrin core to suppress the dye aggregation for a push–pull zinc porphyrin, the PSSC achieved a record 12.3% in 2011 with co-sensitization of an organic dye and a cobalt-based electrolyte. The best PSSC system exhibited a panchromatic feature for light harvesting covering the visible spectral region to 700 nm, giving opportunities to many other porphyrins, such as fused and dimeric porphyrins, with near-infrared absorption spectral features, together with the approach of molecular co-sensitization, to enhance the device performance of PSSC. According to this historical trend for the development of prospective porphyrin sensitizers used in PSSC, we review systematically the progress of porphyrins of varied kinds, and their derivatives, applied in PSSC with a focus on reports during 2007–2012 from the point of view of molecular design correlated with photovoltaic performance.

https://ir.nctu.edu.tw:443/bitstream/11536/20810/1/000311968700017.pdf

Porphyrin-sensitized solar cells

Artificial Molecular Rotors

Bipyridine: the most widely used ligand. A review of molecules comprising at least two 2,2'-bipyridine units.

Porphyrin-based photosensitizers for use in photodynamic therapy

A new class of porphyrin-based chromophore systems has been prepared from ethyne-elaborated porphyrin synthons through the use of metal-mediated cross-coupling methodologies. These systems feature porphyrin chromophores wired together through single ethynyl linkages. This type of topological connectivity affords exceptional electronic interactions between the chromophores which are manifest in their room temperature photophysics, optical spectroscopy, and electrochemistry; these spectroscopic signatures indicate that these species model many of the essential characteristics of biological light-harvesting antenna systems.

https://science.sciencemag.org/content/sci/264/5162/1105.full.pdf

Highly conjugated, acetylenyl bridged porphyrins: new models for light-harvesting antenna systems

Metal-mediated cross-coupling methodologies have been successfully employed to porphyrinic systems, providing a powerful, versatile, and general synthetic approach for the fabrication of elaborated porphyrin structures

Facile elaboration of porphyrins via metal-mediated cross-coupling

A new method for the regulation of the photophysical properties of highly conjugated porphyrin arrays is described. The absorptive and emissive signatures of such supramolecular structures can be modulated to an impressive degree by regulation of: i) the extent of the steric interactions that define the barrier to rotation about the conjugated bridge between the porphyrin chromophores, and ii) the magnitude of ground state chromophore–chromophore electronic communication within the supermolecule. The power of this approach is illustrated by the straightforward synthesis as well as the electronic and emission spectra of eight different porphyrin arrays in which (5,10,15,20-tetraphenylporphinato)zinc(11) and (10,20-diphenylporphinato)zinc(11) complexes are joined by ethyne or butadiyne groups. The points of connectivity of these bridges between the chromophoric building blocks are systematically varied to produce a series of supramolecular structures with meso-to-meso, meso-to-β, or β-to-β linkage topologies. These variations allow excellent control of the ground- and excited-state characteristics of the arrays in the series by regulating the degree of both excitonic and electronic porphyrin-to-porphyrin coupling. Our approach shows the precision with which photophysical properties can be engineered in appropriately designed supramolecular systems.

The Role of Porphyrin‐to‐Porphyrin Linkage Topology in the Extensive Modulation of the Absorptive and Emissive Properties of a Series of Ethynyl‐ and Butadiynyl‐Bridged Bis‐ and Tris(porphinato)zinc Chromophores

The photophysical properties of a series of ethynyl-bridged (porphinato)zinc(II) oligomers have been investigated over the femtosecond and picosecond time scales using ultrafast magic angle and polarized pump−probe spectroscopy. Bis[(2,2‘,-5,10,15,20-tetraphenylporphinato)zinc(II)]ethyne, bis[(5,5‘,-10,20-diphenylporphinato)zinc(II)]ethyne, and 5,15-bis{[(5‘,-10‘,20‘-diphenylporphinato)zinc(II)]ethynyl}[10,20-diphenylporphinato]zinc(II) exhibit rapid (≤150 fs) formation of the emitting state following Soret photoexcitation, nearly an order of magnitude faster than the ∼1 ps S2 → S1 internal conversion observed for a monomeric (porphinato)zinc(II) complex that bears an ethyne moiety fused directly to its macrocycle carbon framework [(5-trimethylsilylethynyl-10,20-diphenylporphinato)zinc(II)]. The femtosecond and picosecond dynamics are strongly influenced by the porphyrin-to-porphyrin linkage topology:  bis[(2,2‘,-5,10,15,20-tetraphenylporphinato)zinc(II)]ethyne, in which a β-to-β ethyne bridge links the t...

Victor S.-Y. Lin

Papers

Highly conjugated, acetylenyl bridged porphyrins: new models for light-harvesting antenna systems

Facile elaboration of porphyrins via metal-mediated cross-coupling

The Role of Porphyrin‐to‐Porphyrin Linkage Topology in the Extensive Modulation of the Absorptive and Emissive Properties of a Series of Ethynyl‐ and Butadiynyl‐Bridged Bis‐ and Tris(porphinato)zinc Chromophores

Ultrafast Dynamics of Highly Conjugated Porphyrin Arrays

Catalytic conversion of simple haloporphyrins into alkyl-, aryl, pyridyl-, and vinyl-substituted porphyrins