Accepted Article This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/php.12767 This article is protected by copyright. All rights reserved. Article type : Research Article Novel Osmium-based Coordination Complexes as Photosensitizers for Panchromatic Photodynamic Therapy Savo Lazic, 1 Pavel Kaspler, 1 Ge Shi, 2 Susan Monro, 2 Tariq Sainuddin, 2 Sarah Forward, 4 Kamola Kasimova, 1 Robie Hennigar, 2 Arkady Mandel, 1* Sherri McFarland, 2,3* and Lothar Lilge 4,5* 1 Theralase Inc, Toronto, ON (Canada) 2 Acadia University, Department of Chemistry, Wolfville, NS (Canada) 3 The University of North Carolina at Greensboro, Department of Chemistry and Biochemistry, Greensboro, NC (USA) 4 University of Toronto Department of Medical Biophysics, Toronto, ON (Canada) 5 Princess Margaret Cancer Centre, Toronto, ON (Canada) * Corresponding Authors: llilge@uhnresearch.ca (Lothar Lilge), samcfarl@uncg.edu (Sherri McFarland), amandel@theralase.com (Arkady Mandel) ABSTRACT Cancer remains a major global malaise requiring the advent of new, efficient, and low-cost treatments. Photodynamic therapy, which combines a photosensitizer and photons to produce cytotoxic reactive oxygen species, has been established as an effective cancer treatment but has yet to become mainstream. One of the main limitations has been the paucity of photosensitizers that are effective over a wide range of wavelengths, can exert their cytotoxic effects in hypoxia, are easily synthesized, and produce few if any side effects. To address these shortfalls, three new osmium-based photosensitizers (TLD1822, TLD1824, and TLD1829) were synthesized and their photophysical and photobiological attributes determined. These photosensitizers are panchromatic (i.e., black absorbers), activatable from 200 to 900 nm, and have strong resistance to photobleaching. In vitro studies show PDT efficacy with both red and near infrared light in normoxic and