# Photophysical and Photochemical Properties of a Curcumins Family: A Combined Computational and Experimental Investigation

## TL;DR

This study investigates curcumin and its derivatives to determine their potential as photosensitizers for photodynamic therapy.

## Contribution

The study combines computational and experimental methods to reveal the photophysical and photochemical mechanisms of curcumin derivatives.

## Key findings

- Enol forms of curcumins are more stable than keto forms.
- Curcumin derivatives can theoretically produce singlet oxygen, essential for photodynamic therapy.
- Curcumin HL4a shows the highest singlet oxygen production yield at ∼15%.

## Abstract

In the present study, photophysical and photochemical
properties
of curcumin (1,7-bis­(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione)
and its seven derivatives, encompassing esterified curcumins and their
bisdemethoxy conjugates have been studied computationally and experimentally
to explore their suitability as photosensitizers for photodynamic
therapy. We found out that enol forms of curcumins are more stable
than keto ones. We observed that the main electronic levels of the
curcumin derivatives well agree with the observed spectroscopic features
(i.e. absorption, fluorescence and phosphorescence
spectra). Based on the spin–orbit coupling matrix elements
and the associated energy gaps, we suggested that the most plausible
mechanism involves excitation from S0 to S1,
followed by intersystem crossing from S1 to T3. Subsequent internal conversion occurs from T3 to T2 and T1, culminating in phosphorescence from T1 to S0. The computed vertical phosphorescence energy
of the first triplet state (T1) for the studied curcumin
derivatives exceed both the computed first excited-state energy of
O21.06 eV in vacuum and 1.05 eV in waterand
the measured value of 0.98 eV in vacuum. These findings indicate that
the studied curcumin derivatives are theoretically capable of photosensitizing
the production of 1O2. In this context, curcumin HL4a exhibits the best yield for singlet oxygen production
(∼15%) and the esterification and the presence of methoxy groups
poorly affect both photophysical and photochemical properties.