| Abstract
| - As models for a self-aggregative, naturally occurring magnesium-chlorin bacteriochlorophyll-dpossessing 31-secondary alcoholic hydroxyl and 131-oxo groups, zinc-chlorins were synthesized with31-oxo and 131-secondary (1) or tertiary hydroxyl groups (2). Compared to the monomers in atetrahydrofuran solution, diastereomers 131R-1R and 131S-1S gave red-shifted absorption maxima(643 → 674 nm in 1R and 708 nm in 1S) in 1 v/v% CH2Cl2−hexane solution, indicating their self-aggregation. Therefore, the positioning of the two groups at 31/131 or 131/31 on the N21−N23molecular (Qy) axis is not necessarily important for the self-aggregation. The 1H NMR and CDspectroscopic studies showed that the 674 nm absorbing species of 1R was characterized as a face-to-face “closed” dimer, while the 708 nm absorbing species of 1S was a large oligomer constructedwith aggregation of head-to-tail “open” dimers. This diastereomeric control over the aggregation of1R and 1S is more pronounced than that observed in the regioisomerically 31-secondary alcoholicR/S-diastereomers 3R and 3S. The difference is ascribable to the conformational fixation of the131-hydroxyl group of the exo five-membered ring in 1. In contrast to self-aggregative 31-tertiaryalcoholic 4, both 131-epimers of 131-tertiary alcoholic 2 were monomeric even in nonpolar organicmedia: the additional 131-methyl group (1 → 2) drastically suppressed the self-aggregation due tothe interference of the methyl group in intermolecular π−π interaction.
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