Aerosolized Droplet Mediated Self-Assembly of Photosynthetic Pigment Analogues and Deposition onto Substrates

Abstract

Self-assembled photosynthetic molecules have a high extinction coefficient and a broad absorption in the infrared region, and these properties can be used to improve the efficiency of solar cells. We have developed a single-step method for the self-assembly of synthetic chlorin molecules (analogues of native bacteriochlorophylls) in aerosolized droplets, containing a single solvent and two solvents, to synthesize biomimetic light-harvesting structures. In the single-solvent approach, assembly is promoted by a concentration-driven process due to evaporation of the solvent. The peak absorbance of Zn(II) 3-(1-hydroxyethyl)-10-phenyl-13(1)-oxophorbine (1) in methanol shifted from 646 nm to 725 nm (∼ 80 nm shift) after assembly, which is comparable to the shift observed in the naturally occurring assembly of bacteriochlorophyll c. Although assembly is thermodynamically favorable, the kinetics of self-assembly play an important role, and this was demonstrated by varying the initial concentration of the pigment monomer. To overcome kinetic limitations, a two-solvent approach using a volatile solvent (tetrahydrofuran) in which the dye is soluble and a less volatile solvent (ethanol) in which the dye is sparingly soluble was demonstrated to be effective. The effect of molecular structure is demonstrated by spraying the sterically hindered Zn(II) 3-(1-hydroxyethyl)-10-mesityl-13(1)-oxophorbine (2), which is an analogue of 1, under similar conditions. The results illustrate a valuable and facile aerosol-based method for the formation of films of supramolecular assemblies.

Energy transfer in aggregates of bacteriochlorophyll c self-assembled with azulene derivatives

“…11,12 Both chlorosomal pigments and their synthetic analogs are intensively studied in this respect. [12][13][14][15][16][17][18][19][20] BChl c forms aggregates in organic nonpolar solvents and also in aqueous environments. In the latter case, addition of a suitable nonpolar compound is necessary to induce the aggregation.…”

Self‐aggregation of Synthetic Zinc Chlorophyll Derivatives Possessing 31‐Hydroxy or Methoxy Group and 131‐Mono‐ or Dicyanomethylene Moiety in Nonpolar Organic Solvents as Models of Chlorosomal Bacteriochlorophyll‐d Aggregates

“…Zinc 3-hydroxymethyl-13 1 -dicyanomethylene-chlorin 1a prepared by modifying naturally occurring Chl-a did self-aggregate in 1% THF-hexane to form large oligomers similar to the corresponding 13 1 -oxo-analog 3a. The artificial self-aggregate is a new model for natural chlorosomal supramolecules (43)(44)(45)(46)(47)(48)(49). Hydrogen bonding of 3 1 -Z-H (Z = NH, NCH 3 , or O) with 13-C=O as well as coordination of 3 1 -Z with central M (=Mg, Zn, Cd) are usually requisite for such self-aggregation (see Fig.…”

Electrospray: More than just an ionization source

“…Shah and Biswas introduced a novel approach employing in‐flight self‐assembly of chlorophyll molecules from a chlorophyll solution. Their assembly was promoted by a concentration‐driven process due to the evaporation of solvents [116]. The authors used a solvent system consisting of two carefully chosen solvents (tetrahydrofuran/ethanol) to obtain a low‐concentration chlorophyll solution in which chlorophyll did not randomly aggregate like when a single solvent is used.…”