Photophysical Properties of Porphyrin Tapes

Abstract

The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso-meso, beta-beta, beta-beta positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, approximately 500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of approximately 1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from approximately 4.5 ps for the T2 dimer to approximately 0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes were observed to be in a sharp contrast to those of the orthogonal porphyrin arrays. The PPP-SCI calculated charge-transfer probability indicates that the lowest excited state of the porphyrin tapes (Tn) resembles a Wannier-type exciton closely, whereas the lowest excited state of the directly linked porphyrin arrays can be considered as a Frenkel-type exciton. Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials.

Synthesis and Characterization of 5,10,15,20-Tetra[3-(3-trifluoromethyl)phenoxy] Porphyrin

“…Porphyrins are molecules that are being vigorously pursued in many areas of research [1][2][3][4][5][6][7][8][9][10][11][12][13]. It has been shown that these molecules are of importance in many applications including, but not limited to, sensors [1][2][3][4][5][6][7], optical memories [8][9][10], and photocatalysis [11][12][13].…”

“…It has been shown that these molecules are of importance in many applications including, but not limited to, sensors [1][2][3][4][5][6][7], optical memories [8][9][10], and photocatalysis [11][12][13]. Many of these applications take advantage of the ability of porphyrins to undergo fast electron transfer.…”

Ultrafast photoresponsive materials and molecular photonics applications by guided wave mode geometry

“…Ultrafast switching materials which work in less than 1 ps are essential for teraherz (THz) communication. Several attempts have been reported for this purpose, which include optical switching by tunneling bi-quantum well semiconductors or organic materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”

“…Since silica-based optical fibers which are employed worldwide in such systems show minimum transmission loss at about 1260-1675 nm, photoresponsive materials are needed to show ultrafast absorption or refractive index changes in such nearinfrared (NIR) region. Many types of ultrafast optical processing devices and semiconductors or organic materials have been studied so far [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Single shot demultiplexing of 1 THz light pulses was proposed on the basis of transient bleaching of organic dye J-aggregate films [3][4][5][6].…”

“…Single shot demultiplexing of 1 THz light pulses was proposed on the basis of transient bleaching of organic dye J-aggregate films [3][4][5][6]. Single-walled carbon nanotubes and expanded porphyrin derivatives are also expected for ultrafast optical switching in the NIR region [7][8][9][10]. All of them employ transient bleaching of NIR absorption at the ground state.…”