Practical Measurement and Reconstruction of Spectral Skin Reflectance

We present two practical methods for measurement of spectral skin reflectance suited for live subjects, and drive a spectral BSSRDF model with appropriate complexity to match skin appearance in photographs, including human faces. Our primary measurement method employs illuminating a subject with two complementary uniform spectral illumination conditions using a multispectral LED sphere to estimate spatially varying parameters of chromophore concentrations including melanin and hemoglobin concentration, melanin blend-type fraction, and epidermal hemoglobin fraction. We demonstrate that our proposed complementary measurements enable higher-quality estimate of chromophores than those obtained using standard broadband illumination, while being suitable for integration with multiview facial capture using regular color cameras. Besides novel optimal measurements under controlled illumination, we also demonstrate how to adapt practical skin patch measurements using a hand-held dermatological skin measurement device, a Miravex Antera 3D camera, for skin appearance reconstruction and rendering. Furthermore, we introduce a novel approach for parameter estimation given the measurements using neural networks which is significantly faster than a lookup table search and avoids parameter quantization. We demonstrate high quality matches of skin appearance with photographs for a variety of skin types with our proposed practical measurement procedures, including photorealistic spectral reproduction and renderings of facial appearance

Investigations about the Chemistry of Tetraarylethene- and Iridium-Based Luminophores

The work described in this thesis focuses on two classes of luminophores: tetraarylethene-based polymers and Ir(III) complexes with orthometalated ligands. Tetraarylethene-based polymers show aggregation-induced emission (AIE) and they are of interest for applications in sensing, imaging, and material science. Ir(III) complexes with orthometalated ligands, on the other hand, can be used as components for light-emitting diodes, and they have been employed as photocatalysts, as building blocks for supramolecular complexes, and as chemo- and bio-sensors. Chapter 2 describes a novel procedure for the synthesis of hyperbranched polyarylethenes via successive electrophilic C-H vinylation reactions of aromatic cores with a triazene. The hyperbranched polyarylethenes display size-dependent luminescence and unusual ratiometric AIE behaviour and they can be applied as sensors for alkali metal cations. In Chapter 3, a clean, fast, and simple procedure for the conversion of fac-Ir(C^N)3 complexes into the thermodynamically less stable mer isomers by a consecutive reaction with first acid (TFA or HNTf2) and then base (NEt3) is reported. The process enables the interconversion of luminophores with distinct photophysical properties and allows accessing mer complexes, which are difficult to synthesize with standard procedures. The possibility of the autonomous fac-to-mer switching was also studied. Chapter 4 describes that the fac isomers of Ir(III) complexes with metalated N heterocyclic carbene ligands, Ir(C^C:)3, can be converted cleanly into the mer isomers when solutions of the complexes are treated with first HNTf2 and then NEt3. The procedure allows obtaining mer-Ir(C^C:)3 in high yields and enables the direct conversion of the mixture of fac and mer isomers of Ir(C^C:)3 into the pure mer isomers. The substituent effect was also studied, and acid-base-induced fac-to-mer isomerization of the bulky Ir(C^C:)3 complex was investigated.LC

Practical acquisition and modeling of spectral reflectance and illumination

Illumination and surface reflectance are the fundamental elements of any virtual scene, which have a major effect on its overall appearance. In reality, although the human eye perceives the incoming light in the form of color, illumination and reflectance have an underlying spectral representation. Considering spectral information of the environment is essential for accurately modeling the real world optical processes, which has a significant role in computer graphics for producing qualitative results in various applications, such as lighting reproduction and spectral rendering. Spectral measurements for complex illuminants and materials are often either not publicly available or exist but are not suited for a particular case scenario. Practically obtaining accurate spectral data is a challenging topic in computer graphics due to the common trade-off between the excessive costs of the specialized equipment and the measurement accuracy. Thus, in this thesis we propose novel methods for acquiring and modeling spectral illumination and reflectance that simultaneously aim at practicality and at the quality of the recovered data. We first introduce our novel practical RGB-to-spectral upsampling method for estimating spectral power distributions of illuminants from RGB photographs, including the legacy RGB environments, without the requirement of any additional information. We then show how the spectrally upsampled RGB illumination can be employed for improved lighting reproduction using an LED sphere. We also present a novel practical method for measuring spectral skin reflectance using a controllable LED sphere and an off-the-shelf dermatological device. We demonstrate how to employ skin measurements to drive the spectral subsurface scattering model with appropriate complexity in order to match the appearance of real skin in photographs. Finally, we implement the spatially varying skin subsurface scattering in a physically-based renderer and validate our proposed measurement technique by generating 3D spectral facial renderings that are, for the first time, comparable to the photographs. The proposed methods are versatile and can potentially be adapted for the general use in spectral rendering pipelines, including real-time implementation, as well as for lighting reproduction applications employing different illumination setups.Open Acces

Synthesis of hyperbranched polyarylethenes by consecutive C–H vinylation reactions

A novel procedure for the synthesis of polyarylethenes is described. Consecutive C–H vinylation reactions of tetraphenylethene with a triphenylethenyl triazene give hyperbranched polyarylethenes of variable sizes. The vinylation reactions are mediated by acid-induced cleavage of the triazene function. In contrast to other procedures for the synthesis of polyarylethenes, our methodology is ‘traceless’, and functional groups are not found in the products. The hyperbranched polyarylethenes show size-dependent luminescence. Larger polymers display increased luminescence in solution but decreased luminescence in the solid state. The polymers exhibit unusual ratiometric aggregation-induced emission. The synthetic methodology can also be used for grafting hyperbranched poly(triphenylethene) to a functional aromatic compound such as benzo-18-crown-6. The coupling product displays a ratiometric luminescence response upon the addition of metal salts.LC

The acid-mediated isomerization of iridium(<scp>iii</scp>) complexes with cyclometalated NHC ligands: kinetic <i>vs.</i> thermodynamic control

The fac isomers of iridium(iii) complexes with metalated N-heterocyclic carbene (NHC) ligands are transformed cleanly into the mer isomers when solutions of the complexes are treated with first HNTf2 and then NEt3.</jats:p

Synthesis of hyperbranched polyarylethenes by consecutive C–H vinylation reactions

&lt;p&gt;Anastasia Yu. Gitlina, Albert Ruggi, Kay Severin*&lt;/p&gt;&lt;p&gt;Synthesis of hyperbranched polyarylethenes by consecutive C–H vinylation reactions&lt;/p&gt;&lt;p&gt;&lt;i&gt;Polym. Chem&lt;/i&gt;. &lt;strong&gt;2023&lt;/strong&gt;, &lt;i&gt;14&lt;/i&gt;, 4182-4187&lt;/p&gt;&lt;p&gt;The dataset contains the following raw data - NMR, HRMS, GPC, TGA, DLS, photophysical data (absorption, excitation, emission spectra, photoluminescence lifetimes and quantum yields).&lt;/p&gt

The acid-mediated isomerization of iridium(iii) complexes with cyclometalated NHC ligands: kinetic vs. thermodynamic control

The isomerization of iridium(III) complexes with metalated N-heterocyclic carbene (NHC) ligands was studied. The fac isomers of complexes with 1-phenyl-3-methylbenzimidazolin-2-ylidene or 1-phenyl-3-benzylbenzimidazolin-2-ylidene ligands are transformed cleanly into the mer isomers when solutions of the complexes are treated with first HNTf2 and then NEt3. The transformation can be accomplished within a few minutes and the side product (NEt3H)(NTf2) is easy to separate. Spectroscopic and structural analyses indicate that the isomerization proceeds by protonation of the carbene ligand at the metalated phenyl group, accompanied by a fac → mer rearrangement of the carbene donors. An iridium complex with a 1-phenyl-1,2,4-triazolo[4,3-f]phenanthridine-based carbene ligand could not be isomerized under similar conditions, most likely because of its reduced conformational flexibility.LC

Spectral upsampling approaches for RGB illumination

We present two practical approaches for high fidelity spectral upsampling of previously recorded RGB illumination in the form of an image-based representation such as an RGB light probe. Unlike previous approaches that require multiple measurements with a spectrometer or a reference color chart under a target illumination environment, our method requires no additional information for the spectral upsampling step. Instead, we construct a data-driven basis of spectral distributions for incident illumination from a set of six RGBW LEDs (three narrowband and three broadband) that we employ to represent a given RGB color using a convex combination of the six basis spectra. We propose two different approaches for estimating the weights of the convex combination using – (a) genetic algorithm, and (b) neural networks. We additionally propose a theoretical basis consisting of a set of narrow and broad Gaussians as a generalization of the approach, and also evaluate an alternate LED basis for spectral upsampling. We achieve good qualitative matches of the predicted illumination spectrum using our spectral upsampling approach to ground truth illumination spectrum while achieving near perfect matching of the RGB color of the given illumination in the vast majority of cases. We demonstrate that the spectrally upsampled RGB illumination can be employed for various applications including improved lighting reproduction as well as more accurate spectral rendering

Acid-base-induced fac → mer isomerization of luminescent iridium(iii) complexes

Luminescent Ir(C^N)3 complexes (C^N = cyclometalated arylpyridine ligand) exist in the form of two stable isomers with distinct photophysical and electrochemical properties: fac and mer. Herein, we show that fac-Ir(C^N)3 complexes can be converted into the thermodynamically less stable mer forms by a consecutive reaction with first acid and then base. The chemically induced isomerization is fast, quantitative, and stereoselective, and it can be inversed by light. The new isomerization process opens the possibility to use highly luminescent Ir(C^N)3 complexes as molecular switches.LC