Nonconventional 1,8-Diazafluoren-9-One Aggregates for Green Light Enhancement in Hybrid Biocompatible Media

Abstract

Organic aggregates currently play a prominent role, mainly for their unique optoelectronic properties in the aggregated state. Such properties can be related to the aggregates’ structure and the molecular packing mode. In the literature, we have well-established models of H and J aggregates defined based on the molecular exciton model. However, unconventional aggregates, the most unrecognized forms, have been generating interest among researchers recently. Within unconventional aggregation, aggregation-induced emission systems (AIE) are considered. In the present work, we discuss the effect of the forming of unconventional aggregation together with the change in dye concentration on the surface energy characteristics of the materials. All materials were prepared as hybrid biocompatible thin films where the matrix is TiO2 or TiO2/carbon nanowalls (CNWs) with the incorporated dye in the form of 1,8-diazafluoren-9-one (DFO). Using the time-resolved emission spectra and the determination of surface parameters from contact angle measurements, we indicated the correlation between the changes in such parameters and the concentration of DFO dye in two types of TiO2 and TiO2/CNW structures. To examine the propensity of DFO for aggregation, the internal energy of the dye was assessed in several aggregate structures using Quantum chemistry calculations. The results emphasize that DFO is an attractive structure in the design of new fluorophores due to its low molecular weight, the presence of a nitrogen atom that provides good coordination properties, and the ability to form hydrogen bonds. Our studies show that when using suitable matrices, i.e., rigid media, it forms the preferred forms of aggregates in the excited state, characterized by high emission efficiency in the band maximum of around 550 nm.

Molecular Design Using Selected Concentration Effects in Optically Activated Fluorescent Matrices

“…In our previous work, we reported on the tendency of DFO molecules to aggregate [12] and investigated the potential for revealing dactyloscopic traces via such aggregates [11]. Importantly, we demonstrated that the enhancement of fingerprint traces can be achieved through the use of DFO aggregates along with DFO-α-amino acid complexes, which represents a novel approach in the field of forensic science.…”

“…Based on previous studies on the DFO molecule, we have gained extensive knowledge of its chemical behavior in various environments, including its photophysical [9][10][11][12] and application properties [11]. Our investigations revealed clear distinctions between the DFO monomer molecule, its complex with α-amino acids, and the aggregate formed as the postulated cyclodimer.…”

“…Based on our previous findings, which suggest that the aggregation processes of DFO are highly susceptible to external environmental factors [12], we needed a medium that would allow us to precisely control the experimental conditions-especially the rigidity of the medium and the DFO concentration. We selected a matrix of polymerized polyvinyl alcohol (PVA) as an ideal medium because it contains -OH groups in the monomer that help disperse DFO inside the polymer network.…”

“…Our group has further contributed to this field by demonstrating that DFO molecules can aggregate and thereby reveal dactyloscopic traces on porous substrates such as plain and thermal papers [9][10][11][12]. Our studies from 2019 to 2022 have delved into the fluorescence properties of DFO and its aggregates across different states of matter, uncovering the dynamic responsiveness of DFO aggregation to environmental changes [9][10][11][12].…”