Mediated Generation of Conjugate Acid by UV and Blue Sensitizers with Upconversion Nanoparticles at 980 nm

Abstract

NIR and UV exposure of systems comprising upconversion nanoparticles (UCNP) based on NaYF4:Tm/Yb@NaYF4, a sensitizer absorbing either in the blue or UV region, and an onium salt with weak coordinating anion resulted in formation of conjugate acid (con‐H+). That was namely Ivocerin (di(4‐methoxybenzoyl)diethylgermane), ITX (2‐iso‐propyl thioxanthone), anthracene, pyrene, rubrene, camphore quinone, and a strong fluorescent coumarin (1,1,6,6,8‐pentamethyl‐2,3,5,6‐tetrahyhdro‐1H,4H‐11‐oxa‐3a‐aza‐benzo[de]anthracene‐10‐one). Quantification occurred by treatment with Rhodamine B lactone whose color switched to intensive red after photolytic formation of con‐H+. Exposure with a NIR laser at 980 nm resulted in less con‐H+ compared to 395 nm where all sensitizers absorb radiation. UCNP did not mainly interfered formation of con‐H+. The different rates obtained in both experiments responsibly explain the failure and success to initiate polymerization of epoxides applying ether 980 nm or 395 nm excitation, respectively.

Rational Selection of Cyanines to Generate Conjugate Acid and Free Radicals for Photopolymerization upon Exposure at 860 nm

“…Alternatively, up‐conversion nanoparticles have received additional attention to initiate photopolymerization either in the UV or blue region. [ 18 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ] Here, absorption of the laser light proceeds at 980 nm while a three‐ and four‐photon absorption results in formation of blue and UV light. [ 40 , 41 ] This was applied to initiate either free‐radical[ 40 , 41 , 42 , 44 , 45 , 47 ] or controlled radical [41] polymerization.…”

“…[ 40 , 41 ] This was applied to initiate either free‐radical[ 40 , 41 , 42 , 44 , 45 , 47 ] or controlled radical [41] polymerization. In addition, these systems can generate conjugate acid [39] to initiate cationic polymerization. [43] Additional interest relating to applications focused on establishing deep cure length (more than 13 cm), [44] and 3D printing [47] that represents some interesting features of these materials.…”

Challenges and limits of upconversion nanoparticles for cationic photopolymerization with UV initiators excited at 980 nm

“…This represents an improvement compared to previous investigations. 10 Nevertheless, this quantity remained different from expectations, where a much higher final conversion of epoxides was expected, but the fact that this system does not distinguish between high and low viscosity systems gives new impetus to the development of systems operating at high viscosities, such as Epikote 357 or similar materials exhibiting high viscosities. This would avoid using systems where the final conversion always appears lower, as in the case of the monomer mixture M2 .…”

Rationale Auswahl von Cyaninen zur Erzeugung von konjugierter Säure und freien Radikalen für die Photopolymerisation durch Belichtung bei 860 nm

“…Alternativ haben aufwärtskonvertierende Nanopartikel zusätzliche Beachtung für die Initiierung der Photopolymerisation im UV oder im blauen Bereich erlangt [18, 39–46] . Hier erfolgt die Absorption des Laserlichts bei 980 nm, während ein Drei‐ oder Vier‐Photonen‐Absorptionsprozess zur Bildung von blauem und UV‐Licht führt [40, 41] .…”

“…Das wurde zur Initiierung der freien radikalischen Polymerisation [40–42, 44, 45, 47] oder zur Aktivierung der kontrollierten radikalischen Polymerisation [41] angewendet. Außerdem können diese Systeme konjugierte Säure generieren, [39] um die kationische Polymerisation zu initiieren [43] . Zusätzliches Interesse in Bezug auf die Anwendungen fokussierte sich auf eine Tiefenaushärtung (mehr als 13 cm Tiefe) [44] und auf den 3D‐Druck, [47] welche einige interessante Eigenschaften dieser Materialien repräsentieren.…”