**Preface to "Exclusive Feature Papers in Colorants"**

Natural colorants have been used from ancient times to colour objects owing to their ability to absorb light mainly within the visible window of the electromagnetic spectrum. Such organic and inorganic dyes and pigments were extracted from flora and fauna resources. In the 19th century, the first synthetic colorants were reported, being the beginning of a new industry related with the development of commercial colorants in the 20th century. The recent advances in strategic knowledge areas such as dyes and materials chemistry, computational resources and technological advances have greatly contributed to the design not only of modern colorants with improved photonic properties, but also to understand the involved photophysical processes via spectroscopic and microscopic techniques. Actually, photoactivatable colorants able to display fluorescence are involved in many light-driven devices and are the cornerstone of many ongoing research projects. These multifunctional colorants are applied in many fields related with biophotonics (diagnosis and therapy), optolectronics (lasers and sensing), photovoltaics (photosensitizers and solar cells) and nanotechnology overall.

This Special Issue project entitled "Exclusive feature papers in colorants" was motivated by such popularity and vast applications of colorants. Along with the following articles and reviews, we intend to highlight some cutting-edge developments in this field through selected works. In particular, the herein included works focus on the design and characterization of new nanomaterials and dyes as pigments and fluorophores, sensors of surrounding physicochemical properties and biomarkers for imaging. Finally, an overview of the state of the art of zinc cation-based complexes as fluorophores is also included.

We hope that the launch of this book could be an inspiration for the readers and a forum to share new ideas and finding around this exciting research topic. We would like to acknowledge Ms. Rachael Zhang for her kind assistance and support during the Special Issue project.

> **Jorge Ba ˜nuelos Prieto, Ugo Caruso** *Editors*

*Article*
