The utility of visible light for 3D printing has increased in recent years owing to its accessibility and reduced materials interactions, such as scattering and absorption/degradation, relative to traditional UV light‐based processes. However, photosystems that react efficiently with visible light often require multiple molecular components and have strong and diverse absorption profiles, increasing the complexity of formulation and printing optimization. Herein, a streamlined method to select and optimize visible light 3D printing conditions is described. First, green light liquid crystal display (LCD) 3D printing using a novel resin is optimized through traditional empirical methods, which involves resin component selection, spectroscopic characterization, time‐intensive 3D printing under several different conditions, and measurements of dimensional accuracy for each printed object. Subsequent analytical quantification of dynamic photon absorption during green light polymerizations unveils relationships to cure depth that enables facile resin and 3D printing optimization using a model that is a modification to the Jacob's equation traditionally used for stereolithographic 3D printing. The approach and model are then validated using a distinct green light‐activated resin for two types of projection‐based 3D printing.

To clarify the cis–trans isomerization mechanism of simple alkenes on the triplet excited state surface, the photochemistry of acyclic and cyclic vinyl ketones with a p-methoxyacetophenone moiety as a built-in triplet sensitizer (1 and 2, respectively) was compared. When irradiated, ketone 1 produces its cis-isomer, whereas ketone 2 does not yield any photoproducts. Laser flash photolysis of ketone 1 yields a transient spectrum with λmax ∼ 400 nm (τ ∼ 125 ns). This transient is assigned to the first triplet excited state (T1) of 1, which presumably decays to form a triplet biradical (1BR) that is shorter lived than the triplet ketone. In comparison, laser flash photolysis of 2 reveals two transients (τ ∼ 20 and 440 ns), which are assigned to T1 of 2 and triplet biradical 2BR, respectively. Density functional theory calculations support the characterization of the triplet excited states and the biradical intermediates formed upon irradiation of ketones 1 and 2 and allow a comparison of the physical properties of the biradical intermediates. As the biradical centers in 2BR are stabilized by conjugation, 2BR is more rigid than 1BR. Therefore, the longer lifetime of 2BR can be attributed to less-efficient intersystem crossing to the ground state.

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Excited-state intramolecular hydrogen transfer on the triplet surface of salicylideneaniline derivatives has received much less attention than the corresponding ultrafast process on the singlet surface. To enhance the understanding of this triplet reactivity, the photochemical properties of a series of salicylidene-α-hydroxy acid salts with different substituents on the phenol moiety (1–3) were characterized. UV/vis absorption and phosphorescence measurements in ethanol revealed that 1–3 exist as both enol and keto tautomers, with the enol form being predominant. Irradiation of 1 at 310 nm in ethanol glass (77 K) yielded an absorption band with a λmax at ∼405 nm, which was assigned to the trans-keto tautomer (trans- 1K). In contrast, laser flash photolysis of 1–3 in methanol or acetonitrile resulted in a transient absorption with λmax at 440–460 nm. This transient, which decayed on the microsecond timescale and was significantly shorter lived in methanol than in acetonitrile, was assigned to the triplet excited state (T1) of the cis-keto tautomer (cis-1K–3K) and residual absorption of trans-1K–3K by comparison with TD-DFT calculations. The assignment of the T1 of cis-1K was further supported by quenching studies with anthracene and 2,5-dimethyl-2,4-hexadiene. Laser flash photolysis of 1 in the temperature range of 173–293 K gave an activation barrier of 6.7 kcal/mol for the decay of the T1 of cis-1K. In contrast, the calculated activation barrier for cis-1K to undergo a 1,5-H atom shift to reform 1 was smaller, indicating that intersystem crossing of the T1 of cis-1K is the rate-determining step in the regeneration of 1.

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