Aggregation of chromophores containing developed aromatic systems may afford two principally different effects: Aggregation Caused Quenching (ACQ)1 and Aggregation Induced Emission (AIE)2. In the last decade the latter attracts growing attention because of unique photophysical properties demonstrated by the AIE chromophores (also called AIEgens). The AIEgens commonly give a strong increase in emission intensity, very often from zero to nearly quantitative quantum yield, due to strong blocking of rotational and vibrational channels of emissive excited state relaxation, which usually are the major reasons of emission quenching. These characteristics form the basis for a wide range of AIEgens applications in electroluminescence, advanced analytics, and especially in medical diagnostics and theranostics.
The major part of studies in this area is related to fluorescent AIEgens, which have been discovered first and investigated in detail. However, aggregation of some types of phosphorescent transition metal complexes such as square-planar Pt(II), Pd(II) and Au(III), which tend to form metallophilic bonding between metal centers in addition to -stacking of the ligands’ aromatic systems, may result in transformation of emissive excited state from the typical ligand centered (3LC) and metal-to-ligand charge transfer (3MLCT) characters, or their mixture, to that determined by the formation of M-M bonds either in ground or excited states.3 The transformation results in a strong bathochromic shift of emission into red and NIR areas of spectrum to fall into so called “window of transparency” of biological tissues without a crucial loss in emission intensity that is of particular importance for the application of these emitters in biomedical research.
It is worth noting, however, that the AIE phenomena are typically observed in solid state where AIEgens are additionally stabilized by rigidity of the chromophore environment. Quite naturally, these emitters are not soluble in water and physiological media that strongly limited their application in biomedicine. In our research group, recently a few methods of solubilizing of the Pt(II) AIEgens have been elaborated, which are based on the use of amphiphilic block-copolymers either as an outer stabilizing matrixes for this type of AIE chromophores or by copolymerization of the platinum complexes with biocompatible polyvinylpyrrolidon using RAFT methodology. Detailed description of the research results will be presented in this lecture together with the analysis of the photophysics of the obtained AIEgens.

Acknowledgements
This study was supported by the grant of Russian Science Foundation, No 24-13-00084.
References
1. J. B Birks,. Photophysics of Aromatic Molecules; Wiley-Interscience, 1970; Vol. 8.
2. J.Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam, B. Z. Tang, Chem Rev 2015, 115, 11718.
3. Y.-C. Wei, K.-H. Kuo, Y. Chi, P.-T. Chou, Acc. Chem. Res. 2023, 56, 689.