5,10‐A₂B₂‐Type meso‐Substituted Porphyrins—A Unique Class of Porphyrins with a Realigned Dipole Moment

Abstract

Current applications in porphyrin chemistry require the use of unsymmetrically substituted porphyrins. Many current industrial interests in optics and biomedicine require systems with either push-pull (electron donating and withdrawing groups) or amphiphilic systems (hydrophobic and hydrophilic groups). In this context we present the class of 5,10-A 2 B 2 -type porphyrins where two different substituents are positioned in diagonally opposite meso positions.Thus, the intramolecular dipole moment in these tetrapyrroles is positioned along a β−β vector passing through two pyrrole rings. This is opposite to the situation of the frequently used 5,15-A 2 BC porphyrins where the dipole moment is oriented along a meso-meso axis. We have elaborated syntheses of the 5,10-A 2 B 2 porphyrins using transition metal catalyzed transformations of 5,10-A 2 porphyrins or direct substitutions reactions thereof which give the target molecules in 22-77 % overall yield. The compounds exhibit interesting structural, spectroscopic and optical features and can serve as building blocks for new porphyrin arrays and applications.

Solvent effect on the nonlinear absorption of 5,10-A2B2meso substituted porphyrins

“…For higher the contribution of the two-photon process to the maximal transmission drop becomes more significant. Thus, more dramatic changes in 10 and with can be expected. Note, that for both H and K, reaches very low values for low .…”

“…18 5 According to a standard five-level Jablonski model, low saturation intensities of the ground state combined with high ratio(s) of the excited state absorption cross-section(s) to the ground state absorption cross-section are indicators of a good OL material. The same applies to the four-level model used to fit 10 the NLA response of 5,10-A 2 B 2 porphyrins. A low saturation intensity allows the saturated regime of one-photon excited state absorption to be quickly accessed with the input intensity.…”

“…The studies on the influence of the four-level model fitting 10 parameters on and showed that the dependence of and on these parameters is complex, and that the effect of a given parameter on the NLA action must be considered in relation to the values of all other parameters. As can be seen from Fig.…”

“…All samples were prepared at a concentration of 2.5.10 -4 M and agitated for about 1 hour in a low power sonic bath prior to the measurements. The scattered light signal was measured simultaneously to the detection of the transmitted laser 10 irradiance in the open Z-scan experiments, with the photodetector placed at 30 o angle to the Z-axis. The experimental data obtained for all compounds in toluene, 15 DMF and chloroform at an input energy of ~50 μJ, which corresponds to an onfocus intensity of about 0.6 GW.cm -2 was fitted (where applicable, i.e.…”

“…The OL response detected for chlorobenzene porphyrin solutions and chloroform/chlorobenzene porphyrin solutions, 5 which developed NLS, can be explained in the following way: in the lower fluence range (<1 J.cm -2 ) the response is dominated by NLA exhibited by the porphyrin, in the higher fluence (>1 J.cm -2 ) range the response is mostly due to NLS. The origin of the scattered light in chlorobenzene and chlorobenzene/chloroform 10 was not investigated further, but it must derive from photochemical processes involving chlorobenzene.…”