Monika Zawadzka

Modeling of Nonlinear Absorption of 5,10-A2B2 Porphyrins in the Nanosecond Regime

The nonlinear absorption (NLA) properties of free base and metalated porphyrins with a unique 5,10-A(2)B(2) substitution pattern were studied with open Z-scan technique at 532 nm in the nanosecond regime over a broad range of input fluence. The NLA responses were found to be dependent on structural features and the solvent used. In most cases, the character of the response differed from that typically observed for other porphyrins under similar experimental conditions (i.e., reverse saturable absorption, RSA), suggesting distinct photophysical properties. A series of models was considered in order to understand the NLA responses. Although the character of the responses varied between compounds and solvents, it was found that one model fits best all of the recorded responses. Thus, a four-level model with simultaneous two-photon absorption arising from the higher excited state is proposed (1 + 1 + 2 photon absorption).

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

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 for which 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 for which the dipole moment is oriented along a meso-meso axis. We have elaborated syntheses of the 5,10-A(2)B(2) porphyrins by using transition-metal-catalyzed transformations of 5,10-A(2) porphyrins or direct substitutions reactions thereof; this gives the target molecules in 22-77% overall yields. The compounds exhibit interesting structural, spectroscopic, and optical features and can serve as building blocks for new porphyrin arrays and applications.

Structural investigation of 5,10-A2B2-type porphyrins: palladium(II) and zinc(II) complexes of 5,10-dibromo-15,20-bis(4-methylphenyl)porphyrin.

The analysis of [5,10-dibromo-15,20-bis(4-methylphenyl)porphyrinato]palladium(II), [Pd(C34H22Br2N4)], and [5,10-dibromo-15,20-bis(4-methylphenyl)porphyrinato](methanol)zinc(II), [Zn(C34H22Br2N4)(CH4O)], reveals a small but localized influence of the bromine residues on the conformation of the macrocycle. A comparison of the 5,10-dibromo substituent pattern with literature data for 5,15-dibromoporphyrins shows similar in-plane distortions in both but a different mix of out-of-plane distortion modes for the different regiochemical arrangements.

Laser induced protonation of free base porphyrin in chloroform results in the enhancement of positive nonlinear absorption due to conformational distortion

Free base porphyrin in chloroform solution irradiated with focused laser beam, in an open Z-scan set-up, changed color from purple to green, which was associated with protonation of the porphyrin with protonic species from photodegradation of the solvent. Protonation is demonstrated as a simple means to improve the optical limiting performance of free base porphyrin nonlinear optical (NLO) materials.

In situ polymerised polypyrrole films for sensors application

Purpose – The purpose of this paper is to present fabrication process of volatile organic compounds (VOCs) sensors based on polypyrrole material deposited on different substrates and to show and compare the responses of the produced sensors to different VOCs. Design/methodology/approach – Polypyrrole sensing layers were prepared by in situ chemical polymerisation on two different substrates: alumina and poly(ethylene terephthalate) (PET). The time of the polymerisation was varied. After film deposition, an interdigitated electrode was screen-printed on the material deposited on the substrate. Findings – It was demonstrated that both polymerisation time and substrate type provide means to vary the sensitivity of polypyrrole-based sensors to VOCs. Practical implications – VOCs, which are released in manufacturing or use of various products and materials, pose a threat to the environment and human health. Therefore, measures must be taken to control their concentration both in indoor and outdoor air. Origina...