# Effect of the naphthylene linker on the J‐aggregation abilities of chlorophyll‐a derivatives

## TL;DR

Researchers found that adding a naphthylene linker to chlorophyll-a derivatives enhances their ability to form J-aggregates with unique optical properties.

## Contribution

The study introduces a new linker design that improves J-aggregation in chlorophyll-a derivatives, enabling larger red-shifts in their optical properties.

## Key findings

- Chl-a derivatives with a 2,6-naphthylene linker showed a larger red-shift (1270 cm−1) in Qy band compared to p-phenylene derivatives (970 cm−1).
- The naphthylene linker promotes single J-aggregation species in micellar solutions, influencing exciton splitting energies.
- Computational studies confirmed that linker structure controls chlorin ring positioning in aggregates.

## Abstract

Chlorophyll(Chl)‐a derivatives inserting an ethynylene‐naphthylene linker between the chlorin π‐skeleton and hydroxymethyl group were prepared as models of chlorosomal Chls. Their syntheses were achieved via Sonogashira coupling reaction. Their J‐aggregation behaviors were investigated by electronic absorption and circular dichroism spectroscopic measurements. These studies revealed that the 2,6‐naphthylene inserted Chl‐a derivatives gave the single J‐aggregation species in an aqueous Triton X‐100 micellar solution with a larger red‐shift value (1270 cm−1) of the Qy band in spite of its longer linker compared with p‐phenylene inserted Chl‐a derivative (970 cm−1). These unique optical properties were also discussed based on the computational studies, which indicated the different positional relation of chlorin rings in the assemblies by the linker structure.

Chlorophyll(Chl)‐a derivatives inserting an ethynylene‐naphthylene linker between the chlorin π‐skeleton and hydroxymethyl group were prepared, and their J‐aggregation behaviors were investigated by electronic absorption and circular dichroism spectroscopic measurements. These studies revealed that the 2,6‐naphthylene inserted Chl‐a derivatives gave a single J‐aggregation species in an aqueous Triton X‐100 micellar solution with a larger red‐shift value of the Qy band despite its longer linker compared with the p‐phenylene inserted Chl‐a derivative reported previously. This result suggested that the linkers could control the positional relationship of the chlorin rings in the self‐aggregates, which have a huge effect on the exciton splitting energies.