Liquid, Two-Photon Absorbing Porphyrins for Optical Limiting

摘要

This report results from a contract tasking Polish Academy of Sciences as follows: The material for real-world optical limiting applications based on RSA has to independently possess (among others) three distinct properties: large two-photon absorption cross-section, long-living excited triplet state and state of liquidity (or at least very high solubility). Currently there is no such material available. Compounds possessing large TPA cross-sections have typically short lived triplet-state. On the other hand compounds which have long-lived triplet-state, usually have small cross- section. The only class of molecules which can fulfill these requirements are porphyrins (or their close analogs like phthalocyanines, corroles etc.). Simple porphyrins have rather low TPA cross-sections (10 GM). There are known ways to increase TPA cross-section in porphyrins. Usually this requires addition of other aromatic moieties to existing chromophore, thus making these molecules even less soluble. Consequently the major challenge will be to introduce high solubility, or better liquidity into porphyrin core. There are a two major ways envisioned: Introduction of substituents, which are known to change physical properties of solids into liquids. Specifically we will focus on functional groups which increase solubility of porphyrins in common organic solvents such as long alkyl chains and oligoethyleneglycol chains. Preparation of ionic liquid derivatives of porphyrins. This is totally new approach, since there is no ionic liquid derivative of porphyrin known. One of the possible pathways is to synthesize imidazolium salts substituted with porphyrin ring. This is more challenging idea which will be pursued in the parallel to the main approach.