# Rh‐Catalyzed [2 + 2 + 2] Cycloaddition of Linked Bis(Diynes) Ar‐C≡C‐C≡C‐(CH2)3‐C≡C‐C≡C‐Ar With Quinones: Synthesis and Photophysical Properties of Bis(Arylethynyl)‐Naphthoquinones and Anthraquinones

## TL;DR

This paper describes a new method to synthesize complex quinone-based compounds using rhodium-catalyzed reactions and microwave radiation, and explores their light-related properties and reactions.

## Contribution

A novel Rh-catalyzed [2 + 2 + 2] cycloaddition method for synthesizing bis(arylethynyl)quinones with microwave-enhanced yields.

## Key findings

- Microwave irradiation significantly improved the yields of the synthesized quinone compounds.
- The synthesized quinones lacked photoluminescence and singlet oxygen luminescence.
- A fluorescent derivative underwent photooxidation under sunlight via sensitized 1O2.

## Abstract

Herein, we report the Rh‐catalyzed [2 + 2 + 2] cycloaddition of linked bis(diynes) Ar‐C≡C‐C≡C‐(CH2)3‐C≡C‐C≡C‐Ar with quinones for the rapid and efficient assembly of rigid structures containing bis(arylethynyl)naphthoquinones or anthraquinones using microwave radiation. The photophysical properties of the products were investigated, including absorption, emission, transient absorption (TA) spectroscopy, and singlet oxygen luminescence studies. However, the quinones did not exhibit photoluminescence or detectable singlet oxygen luminescence. Computational analysis via density functional theory (DFT) was performed to elucidate the electronic and structural factors influencing their behavior. Moreover, reductive methylation of one of the bis(arylethynyl)naphthoquinones (3aa) generated the fluorescent bis(methoxy) naphthalene derivative 4aa (Φf
= 0.53). However, 4aa underwent photooxidation in air under sunlight via reaction with 1O2, which it sensitized, leading to ring opening of the bis(methoxy)arene ring.

We report the synthesis bis(arylethynyl)naphtho‐ and anthraquinones via Rh(I)‐catalyzed [2 + 2 + 2] cycloaddition reactions. The substrate scope of both quinones and linked bis‐diynes was explored. Microwave irradiation remarkably enhanced yields. A fluorescent bis(methoxy)‐bis(arylethynyl)naphthalene was synthesized, which underwent an unusual photooxidation in air under sunlight.