1. By
Amina Tariq

2.  Interest in Dyes
 PDT: A modern application of photoactive
dyes
 Project Aims
 Chemical Strategy
 Dark and Light Promoted Reactions
 Reaction Highlights
 Challenges
 Future Work
 References

3.  Broad spectrum of applications owing to unique physio-
chemical properties
 Synthesis of dyes is what revolutionised the synthetic
organic chemistry
 Cover the full spectrum in particular yellow, red and
oranges/complete rainbow of colours
 Intense bright colours with good fastness properties
 Extensively utilised in pharmaceutical, cosmetics, food,
dyeing/textiles, printing and analytical chemistry
 Medically important as they are well-known for their
antibiotic, antifungal and anti-HIV properties

4. Mauveine Neutral red Methylene blue

5.  Photoactive – A
substance/compound is considered
photoactive if it is capable of absorbing
light of appropriate wavelength, and as
a result of this light absorption
undergoes various photochemical and
photophysical events mainly
Fluorescence and Phosphorescence.
 Photodynamic Therapy
(PDT)- A type of treatment that
involves the use of a light-sensitive
medication (photoactive dye) and a
source of light to destroy abnormal
cells.

6. Neutral Red
• Triplet-photosensitizer
• Photoredox catalyst
• Low quantum yield
Targeted compounds
(1)
(3)
(4)
(5)

7. Diazo component Diazonium salt
Coupling component

8. 1. Reduced form of the salt is the major
product
2. Other side products
3. Target compound is in low yield
4. Reduced form highly stable/high redox
potential
5. High activation barrier

9. 1. Using a light source helps to
overcome the activation barrier
2. Reaction goes to completion
3. Targeted compound isolated in
good yield
4. Reaction is reproducible

10.  Instability of “Aryl Diazonium Salt” under RT
 Determination of the reaction mechanism is
required to establish right conditions

11.  Simple and cheap, easy to handle reagents, readily
available
 Mild reaction conditions
 No need to use organometallic reagents as Neutral
Red autocatalyses the reaction
 Low environmental impact due to use of water as a
solvent
 Easy to scale-up

12.  Study of photo- and electrochemistry of diazonium
salt of Neutral Red to understand the mechanistic
pathways
 Acquire details of photoredox chemistry of
participating reagents and intermediates to better
understand the kinetics of the reaction

13.  CHEMIK 2012, 66, 12, 1298-1307
 MUHAMMAD A RAUF, A.A.S., MUHAMMAD KHATTAB. Solvent effects on the spectral properties of Neutral Red. Chemistry Central
Journal, 2008, 2(19).
 BINDEWALD, E., R. LORENZ, O. HUBNER, D. BROX, D.-P. HERTEN, E. KAIFER and H.-J. HIMMEL. Tetraguanidino-functionalized phenazine
and fluorene dyes: synthesis, optical properties and metal coordination. Dalton Transactions, 2015, 44(7), pp.3467-3485.
 SINGH, M.K., H. PAL and A.V. SAPRE. Studies on the Radiolytically Produced Transients of Neutral Red: Triplet and Reduced
Radicals. Photochemistry and Photobiology, 2000, 71(1), pp.44-52.
 WAINWRIGHT, M. Dyes in the development of drugs and pharmaceuticals. Dyes and Pigments, 2008, 76(3), pp.582-589.
 MARKS, G.T., LEE, E. D., AIKENS, D. A. AND RICHTOL, H. H. TRANSIENT PHOTOCHEMISTRY OF NEUTRAL RED. Photochemistry
and Photobiology, 1984, 39, pp.323–328.
 WAINWRIGHT, M. Photodynamic therapy – from dyestuffs to high–tech clinical practice. Review of Progress in Coloration and
Related Topics, 2004, 34(1), pp.95-109.
 MURUBE, J. Rose Bengal: The Second Most Commonly Used Surfocular Vital Stain. The Ocular Surface, 2014, 12(1), pp.14-22.
 MINGLIANG HAN, X.Z., XIAOXIA ZHANG, CHAOQIANG LIAO, BAIQING ZHU, QIAOLING LI. Azo-coupled zinc phthalocyanines:
Towards broad absorption and application in dye-sensitized solar cells. Polyhedron, 2015, 85, pp.864-873.
 BONNETT, R. Photosensitizers of the porphyrin and phthalocyanine series for photodynamic therapy. Chemical Society
Reviews, 1995, 24(1), pp.19-33.
 ANA P. CASTANO, T.N.D., MICHAEL R, HAMBLIN. Mechanisms in photodynamic therapy: part one-photosensitizers,
photochemistry and cellular localization. Photodiagnosis and Photodynamic Therapy, 2004, 1(4), pp.279-293.
 LASTOVOI, A.P., A.A. IGNATOVA, A.V. FEOFANOV, E.A. MACHINSKAYA and V.I. IVANOVA-RADKEVICH. Properties of the Novel
Photosensitizer β,β,β′,β′-Tetramethyltribenzotetraazachlorin. Pharmaceutical Chemistry Journal, 2014, 48(2), pp.77-81.

14. Dr. Natalia Sergeeva
Dr. Terry Key
Ana Maria Garrote Canas
Ellana Beard
Department of Colour Science
Faculty of Mathematics and Physical Sciences at
University of Leeds

15. Thank you