The CoeusCy7 project included six work packages and multiple interdisciplinary activities. Work performed so far and main results per work package:
WP 1 – Included planning, management, and project coordination. It covered finances, budgeting, and task scheduling. A career development plan was prepared in collaboration with supervisors, addressing training, publication planning, and conference participation.
WP 2 – Consisted of familiarizing the researcher with the new facilities, hands-on training with analytical instrumentation (e.g. HPLC, LC-MS, HRMS, etc.), including an introduction to NMR facilities, and various other spectroscopic and photophysical equipment. Additionally, the synthetic methodology was discussed and established during this time. Complementary and transferable skills training included grant writing training and project management training.
WP 3 and WP 4 – Included the attempts to synthesize the desired heptamethine cyanine derivatives, which have one C=C double bond in Z-configuration. After numerous unsuccessful attempts, we observed that the precursors (Zinke salts) do not undergo Zinke–type ring opening, despite exploring various reaction conditions, such as different solvents, reaction temperatures, and starting materials. Instead, precursors undergo reversible nucleophilic addition to the C2 carbon with subsequent recovery of the starting materials. After this finding, we explored other synthetic approaches, but the desired products remained elusive. These results raised questions about the nature of heptamethine cyanine dyes with a Z-configuration of the C=C double bond in the chain. To better understand these dyes, we took a completely different approach. We conducted an in-depth, two-part study of the prototypical heptamethine cyanine dye, described in following work package.
WP 5 – An extensive photophysical and photochemical characterization of heptamethine cyanines was conducted. First, a detailed spectroscopic analysis was carried out using femtosecond stimulated Raman spectroscopy combined with quantum chemical calculations. This analysis provided a most comprehensive picture of the species produced during heptamethine cyanine excitation and how they behave on the femtosecond to sub-millisecond timescale. Inspired by the ultrafast photoinduced electron transfer to dissolved oxygen observed in the spectroscopic analysis, we investigated an unexpected photodegradation pathway of a prototypical heptamethine cyanine dye using a comprehensive analytical approach to elucidate the underlying mechanism. This approach included kinetic studies, isotopic labeling, femtosecond transient absorption spectroscopy, femtosecond stimulated Raman spectroscopy, collision-induced dissociation, and infrared photodissociation spectroscopy, amongst other methods. The results provided a detailed mechanistic picture of the photodegradation pathway of prototypical heptamethine cyanine dye often used in bioimaging.
Lastly, within WP 6, the dissemination of the project results, insights, and achievements to the scientific community was achieved by publishing two scientific papers, as well as three oral presentations at conferences. Communication to the general public was achieved by presenting in seminars, social media, and websites.
