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HRS measurements use near\u2010infrared excitation and are performed under continuous UV irradiation to drive photoswitching. To compute (non)linear optical properties of explicitly solvated systems, an all\u2010atom dynamic structure quantum mechanical (ADQM) protocol is proposed, coupling GFN2\u2010xTB molecular dynamics with the eXact integral simplified TD\u2010DFT (XsTD\u2010DFT). XsTD\u2010DFT enables efficient evaluation of absorption and second harmonic generation at a fraction of TD\u2010DFT cost, capturing chromophore\u2013solvent interactions for systems of hundreds of atoms. Predicted first hyperpolarizabilities show striking agreement with HRS measurements, demonstrating the adequacy of ADQM methodologies. To rationalize the origin of the NLO response, we introduce a scheme combining partial least squares regression with non\u2010equilibrium MD geometries, uncovering key structural and electronic parameters governing the HRS response of MC. Finally, the ADQM protocol estimates the  photoconversion efficiency (2%) under continuous UV irradiation and quantifies the HRS contrast upon photoswitching. Overall, this work establishes a robust, computationally efficient framework for predicting molecular NLO properties directly comparable to experiment, illustrating how seamless integration of theory and spectroscopy yields deep structure\u2013property insights for designing NLO photoswitchable\u00a0materials.<\/jats:p>","DOI":"10.1002\/chem.71669","type":"journal-article","created":{"date-parts":[[2026,9,17]],"date-time":"2026-09-17T12:08:28Z","timestamp":1789646908000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Second Harmonic Generation of Spiropyran\u2013Merocyanine Photoswitches: Insights From Hyper\u2010Rayleigh Scattering and All\u2010Atom Dynamic Structure Quantum Mechanical Calculations"],"prefix":"10.1002","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-3877-6546","authenticated-orcid":false,"given":"Maril\u00f9 G.","family":"Maraldi","sequence":"first","affiliation":[{"name":"Theoretical Chemistry Group, Molecular Chemistry Materials and Catalysis Division (MOST), Institute of Condensed Matter and Nanosciences Universit\u00e9 Catholique de Louvain Louvain\u2010la\u2010Neuve Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-6133-146X","authenticated-orcid":false,"given":"Maxime","family":"Devuyst","sequence":"additional","affiliation":[{"name":"Molecular Chemistry Materials and Catalysis Division (MOST), Institute of Condensed Matter and Nanosciences Universit\u00e9 Catholique de Louvain Louvain\u2010la\u2010Neuve Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6804-9757","authenticated-orcid":false,"given":"Vincent","family":"Rodriguez","sequence":"additional","affiliation":[{"name":"Universit\u00e9 de Bordeaux, CNRS, Bordeaux INP Institut des Sciences Mol\u00e9culaires Talence France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6622-2402","authenticated-orcid":false,"given":"Fr\u00e9d\u00e9ric","family":"Castet","sequence":"additional","affiliation":[{"name":"Universit\u00e9 de Bordeaux, CNRS, Bordeaux INP Institut des Sciences Mol\u00e9culaires Talence France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9564-7303","authenticated-orcid":false,"given":"Marc","family":"de Wergifosse","sequence":"additional","affiliation":[{"name":"Theoretical Chemistry Group, Molecular Chemistry Materials and Catalysis Division (MOST), Institute of Condensed Matter and Nanosciences Universit\u00e9 Catholique de Louvain Louvain\u2010la\u2010Neuve Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2026,9,17]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1021\/accountsmr.4c00125"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.1038\/s41563\u2010024\u201001820\u20104"},{"key":"e_1_2_8_4_1","doi-asserted-by":"publisher","DOI":"10.1038\/s43246\u2010024\u201000707\u2010w"},{"key":"e_1_2_8_5_1","doi-asserted-by":"crossref","first-page":"543","DOI":"10.1039\/D2NH00532H","article-title":"A Photonic Artificial Synapse With a Reversible Multifaceted Photochromic Compound","volume":"8","author":"Sharma D.","year":"2023","journal-title":"Nanoscale Horizons"},{"key":"e_1_2_8_6_1","doi-asserted-by":"publisher","DOI":"10.1021\/ar4000955"},{"key":"e_1_2_8_7_1","doi-asserted-by":"crossref","first-page":"505","DOI":"10.1021\/jz502477m","article-title":"Reversible Photoswitching of the Interfacial Nonlinear Optical Response","volume":"6","author":"Schulze M.","year":"2015","journal-title":"Journal of Physical Chemistry Letters"},{"key":"e_1_2_8_8_1","doi-asserted-by":"crossref","first-page":"10861","DOI":"10.1021\/jacs.3c02778","article-title":"Nonlinear Optical Responses of Photoswitchable Donor\u2010Acceptor Stenhouse Adducts","volume":"145","author":"Dubuis S.","year":"2023","journal-title":"Journal of the American Chemical Society"},{"key":"e_1_2_8_9_1","doi-asserted-by":"publisher","DOI":"10.1021\/acs.jpcc.5c01204"},{"key":"e_1_2_8_10_1","doi-asserted-by":"publisher","DOI":"10.1039\/D4CP03674C"},{"key":"e_1_2_8_11_1","doi-asserted-by":"crossref","first-page":"5638","DOI":"10.1021\/jp711511t","article-title":"Investigation on the Second\u2010Order Nonlinear Optical Responses in the Keto\u2010Enol Equilibrium of Anil Derivatives","volume":"112","author":"Plaquet A.","year":"2008","journal-title":"Journal of Physical Chemistry C"},{"key":"e_1_2_8_12_1","doi-asserted-by":"crossref","first-page":"275","DOI":"10.1002\/chem.19950010504","article-title":"Light\u2010Triggered Molecular Devices: Photochemical Switching of Optical and Electrochemical Properties in Molecular Wire Type Diarylethene Species","volume":"1","author":"Gilat S. 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