Color Change Effect in an Organic-Inorganic Hybrid Material Based on a Porphyrin Diacid

摘要

Porphyrinic materials show a range of interesting and useful optical andelectrical properties. The less well-known sub-class of porphyrin diacids hasbeen used in this work to construct an ionic hybrid organic-inorganic materialin combination with a halogenidometalate anion. The resulting compound,$[H_6TPyP][BiCl_6]_2$ (1) (TPyP = tetra(4-pyridyl)porphyrin) has been obtainedvia a facile solution based synthesis in single crystalline form. The materialexhibits a broad photoluminescence emission band between 650 and 850 nm at roomtemperature. Single crystals of $[H_6TPyP][BiCl_6]_2$ show a photocurrent inthe fA and a much higher dark current in the nA range. They also display anunexpected reversible color change upon wetting with different liquids. Thisphenomenon has been investigated with optical spectroscopy, SEM, XPS and NEXAFStechniques, showing that a surface-based structural coloration effect is thesource of the color change. This stands in contrast to other materials wherestructural coloration typically has to be introduced through elaborate,multi-step processes or the use of natural templates. Additionally, itunderscores the potential of self-assembly of porphyrinic hybrid compounds inthe fabrication of materials with unusual optical properties.