Why Do Silver Trimers Intercalated in DNA Exhibit Unique Nonlinear Properties That Are Promising for Applications?

Our investigation of one-photon absorption (OPA) and nonlinear optical (NLO) properties such as two-photon absorption (TPA) of silver trimer intercalated in DNA based on TDDFT approach allowed us to propose a mechanism responsible for large TPA cross sections of such NLO-phores. We present a concept that illustrates the key role of quantum cluster as well as of nucleotide bases from the immediate neighborhood. For this purpose, different surroundings consisting of guanine-cytosine and adenine-thymine such as (GCGC) and (ATAT) have been investigated that are exhibiting substantially different values of TPA cross sections. This has been confirmed by extending the immediate surroundings as well as using the two-layer quantum mechanics/molecular mechanics (QM/MM) approach. We focus on the cationic closed-shell system and illustrate that the neutral open-shell system shifts OPA spectra into the NIR regime, which is suitable for applications. Thus, in this contribution, we propose novel NLO-phores inducing large TPA cross sections, opening the route for multiphoton imaging.