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Abstract <p>The effect of acid on the spectral and photochemical properties of the covalently bonded biphotochromic dyad <b>D44B</b>, containing two styrylbenzo[f]quinoline photochromes, has been studied. The [2+2] photocycloaddition (PCA) reaction forms cyclobutane <b>CB44B</b>. It has been shown that to impart sensitivity to visible light, it is sufficient to convert only part of the dyad into a cationic form, which has a bathochromically shifted absorption spectrum. This allows for the selective excitation of only the dyad cation by visible light and the initiation of the proton-catalyzed PCA reaction in the λ-orthogonal mode. The photochemical activity of the dyad cation has been found to decrease compared to the neutral dyad, the decline that according to quantum chemical DFT calculations is associated with a change in the structure of the frontier molecular orbitals occupied in the excited state. A general conclusion has been reached that small additions of acid can expand the spectral range of photochromes containing nitrogen-containing six-membered heterocyclic rings, shifting it into the visible region, and use relatively soft light for switching the photochrome.</p>

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Proton as a Catalyst for Long-Wavelength Sensitivity of Bis-Styrylbenzoquinoline Dyad

  • 期刊论文

  • 发表日期：

    2026年2月1日

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  • M. F. Budyka,
  • V. M. Li,
  • N. I. Potashova

摘要

Abstract

The effect of acid on the spectral and photochemical properties of the covalently bonded biphotochromic dyad D44B, containing two styrylbenzo[f]quinoline photochromes, has been studied. The [2+2] photocycloaddition (PCA) reaction forms cyclobutane CB44B. It has been shown that to impart sensitivity to visible light, it is sufficient to convert only part of the dyad into a cationic form, which has a bathochromically shifted absorption spectrum. This allows for the selective excitation of only the dyad cation by visible light and the initiation of the proton-catalyzed PCA reaction in the λ-orthogonal mode. The photochemical activity of the dyad cation has been found to decrease compared to the neutral dyad, the decline that according to quantum chemical DFT calculations is associated with a change in the structure of the frontier molecular orbitals occupied in the excited state. A general conclusion has been reached that small additions of acid can expand the spectral range of photochromes containing nitrogen-containing six-membered heterocyclic rings, shifting it into the visible region, and use relatively soft light for switching the photochrome.