Search

The use of light for shaping and changing matter is of high relevance in polymer and material science. Herein, a photopolymer method is presented, which comprises the combination of 3D photo-printing at 405 nm light and subsequent modification under two-photon absorption (TPA) conditions at 532 nm light, adding the fourth dimension. The TPA-triggered cycloreversion reaction of an intramolecular coumarin dimer (ICD) structure occurs within the absorbing material. The 3D-printable matrix does not show any degradation under the TPA conditions. With the presented photochemical tool of TPA processes inside absorbing 3D photo-printable matrices, new possibilities for post-printing modification, e. g. for smart materials, are added., (© 2023 The Authors. Macromolecular Rapid Communications published by Wiley-VCH GmbH.)

High-refractive-index polymers for intraocular lenses are presented whose refractive index can be tuned post-operatively in a non-invasive manner to enable focal length and aspheric corrections in vivo. The polymer materials contain covalently attached photochemically crosslinkable coumarin side groups, to cause a change in refractive index of Deltan > 0.02, which enables one to tune the focal length of a standard IOL by two diopters. This is enough to ensure that more than 80% of all cataract patients can be adjusted non-invasively to optimal vision after cataract surgery, thus providing a remedy to a major shortcoming of today's cataract surgery.

Abstract: The photocleavage of a coumarin derivative dimer is a promising mechanism for laser controlled drug release in medical applications. We studied the efficiency of such reaction after two-photon excitation, comparing femtosecond and nanosecond pulses in the range from 400 to 800nm. The photocleavage reaction is remarkably more efficient for shorter wavelengths. The spectral profile of the two-photon absorption (TPA) spectrum resembles the single-photon absorption (SPA) spectrum. It was also observed that the photocleavage reaction triggered with femtosecond pulses is about 4.9×104 times more efficient than the reaction with nanosecond pulses at the same wavelength and beam area. [Copyright &y& Elsevier]

Photochemical reactions induced by two-photon-absorption processes offer several advantages over common one-photon initiated photoreactions, e.g., three-dimensional spatial control. We present the photocleavage reaction of coumarin photodimers via a two-photon process using pulsed frequency-doubled Nd:YAG-laser light. The two-photon-induced cycloreversion reaction leads selectively to the cleavage of the coumarin photodimers resulting in the formation of monomeric coumarin molecules. The two-photon cross section of the coumarin photodimer was determined to be of 1.6×10−52 cm4 s photon−1. The presented reaction is of interest, e.g., for the photo-triggered release of chemicals in areas which cannot be directly optically addressed due to cover layers which have a high absorption at the single-photon-absorption wavelength. [Copyright &y& Elsevier]