Biomimetic self-assembling acylphthalocyanines.

We synthesized a series of biomimetic self-assembling phthalocyanines equipped with carbonyl groups as recognition motifs, a central zinc atom and diverse solubilizing alkyl chains mimicking for the first time with these robust pigments the natural chlorosomal bacteriochlorophylls. Upon self-assembly a very broad and red-shifted Q-band absorption extending to over 900 nm is put into evidence.

Ultrafast Dynamics of meso-Tetraphenylmetalloporphyrins: The Role of Dark States.

Studying the relaxation pathways of porphyrins and related structures upon light absorption is crucial to understand the fundamental processes of light harvesting in biosystems and many applications. Herein, we show by means of transient absorption studies, following Q- and Soret-band excitation, and ab initio calculations on meso-tetraphenylporphyrinato magnesium(II) (MgTPP) and meso-tetraphenylporphyrinato cadmium(II) (CdTPP) that electronic relaxation following Soret-band excitation of porphyrins with a heavy central atom is mediated by a hitherto disregarded dark state. This accounts for an increased rate of internal conversion. The dark state originates from an orbital localized at the central nitrogen atoms and its energy continuously decreases along the series from magnesium to zinc to cadmium to below 2.75 eV for CdTPP dissolved in tetrahydrofuran. Furthermore, we are able to directly trace fast intersystem crossing in the cadmium derivative, which takes place within (110±20) ps.

Programmed metalloporphyrins for self-assembly within light-harvesting stacks: (5,15-dicyano-10,20-bis(3,5-di-tert-butylphenyl)porphyrinato)zinc(II) and its push-pull 15-N,N-dialkylamino-5-cyano congeners obtained by a facile direct amination.

The title dicyano compound was synthesized via cyanation and it self-assembles in nonpolar solvents giving red-shifted and broad absorption maxima just as the bacteriochlorophylls which are encountered in the light-harvesting organelles of early photosynthetic bacteria. In the crystal, stacks are formed through a hierarchic combination of pi-stacking and a CN-Zn electrostatic interaction. Push-pull 15-N,N-dialkylamino-5-cyano congeners could be obtained in high yields using a solvent- and catalyst-free direct amination of meso-bromoporphyrins. Importantly, the fluorescence of the self-assembled species due to the very orderly manner in which the chromophores are arranged is not entirely quenched and has a surprisingly long lifetime of over 1 ns. This lends hope of using the trapped energy in biomimetic hybrid solar cells.