Anna Mauri

Coordination polymers (CPs) represent an innovative class of materials with proven potential for multiphoton absorption applications. However, understanding the structure‐property relationships that govern their nonlinear optical behavior remains challenging. This study presents an in‐depth investigation of the effects of intermolecular interactions on multiphoton absorption by focusing on the synthesis and characterization of 1,6,7,12‐tetrachloroperylenediimide‐N,N'‐di‐(acetic acid) ( H ₂ tpda ) and its coordination with zinc to form [Zn ₂ tpda(DMA) ₂ (DMF) _0.3 ] ( Zntpda ). How the packing of tpda linkers within the coordination framework influences their optical properties is revealed. The analysis demonstrates that Zntpda exhibits a broadened UV–vis absorption spectrum with no emission indicative of H‐type aggregation with additional evidence of a photo‐induced electron transfer. Z‐scan measurements show enhanced two‐photon absorption (2PA) cross‐sections of Zntpda compared to H ₂ tpda and even three‐photon absorption (3PA). This is explained by intermolecular interactions, electronic coupling, and spatial confinement effects within the polymer. The findings underscore the critical role of chromophore orientation and packing in optimizing nonlinear optical performance, offering insights for designing advanced functional CP materials tailored for photonic applications.

In the rapidly evolving field of 3D laser nanoprinting, achieving high resolution and high printing speed relies heavily on the effective use and design of sensitive photoinitiators. However, their photoreactivity is hitherto not well described. This study investigates the photochemical and photophysical characteristics of a high‐performing Norrish Type II photoinitiator (2 E ,6 E )‐2,6‐bis(4‐(dibutylamino)benzylidene)‐4‐methylcyclohexanone, known as BBK, as well as commonly employed Norrish Type I photoinitiators: Irgacure 651, Irgacure 369. Using quantum mechanical calculations, multiphoton absorption, the formation of the excited states, and the radical formation mechanisms most probably involved in the initiation of free radical polymerization are examined. Their relation to the observations during 3D printing experiments is discussed, aiming to uncover the molecular foundations behind varying performances of photoinitiators. Bond dissociation energies and energy barriers for bond cleavage of Irgacure photoinitiators are demonstrated to confirm radical formation in the lowest triplet state, whereas this pathway is shown to be less probable for BBK. The radical polymerization initiation upon absorption from the triplet manifold of BBK and reactions with pentaerythritol triacrylate (PETA) monomers are described. Deactivation pathway via reversible intersystem crossing, as well as the photoactivation characteristics, are compared with relation to the 7‐diethylamino‐3‐thenoylcoumarin (DETC) photoinitiator.

The performance of a photoinitiator is key to control efficiency and resolution in 3D laser nanoprinting. Upon light absorption, a cascade of competing photophysical processes leads to photochemical reactions toward radical formation that initiates free radical polymerization (FRP). Here, we investigate 7-diethylamino-3-thenoylcoumarin (DETC), belonging to an efficient and frequently used class of photoinitiators in 3D laser printing, and explain the molecular bases of FRP initiation upon DETC photoactivation. Depending on the presence of a co-initiator, DETC causes radical generation either upon two-photon- or three-photon excitation, but the mechanism for these processes is not well understood so far. Here, we show that the unique three-photon based radical formation by DETC, in the absence of a co-initiator, results from its excitation to highly excited triplet states. They allow a hydrogen-atom transfer reaction from the pentaerythritol triacrylate (PETA) monomer to DETC, enabling the formation of the reactive PETA alkyl radical, which initiates FRP. The formation of active DETC radicals is demonstrated to be less spontaneous. In contrast, photoinitiation in the presence of an onium salt co-initiator proceeds via intermolecular electron transfer after the photosensitization of the photoinitiator to the lowest triplet excited state. Our quantum mechanical calculations demonstrate photophysical processes upon the multiphoton activation of DETC and explain different reactions for the radical formation upon DETC photoactivation. This investigation for the first time describes possible pathways of FRP initiation in 3D laser nanoprinting and permits further rational design of efficient photoinitiators to increase the speed and sensitivity of 3D laser nanoprinting.