High‐level Ab Initio Absorption Spectra Simulations of Neutral, Anionic and Neutral+ Chromophore of Green Fluorescence Protein Chromophore Models in Gas Phase and Solution

Semiclassical ab initio simulations of the absorption spectra of neutral and anionic p ‐hydroxybenzylidene‐2,3‐dimethylimidazolinone ( p ‐ HBDI ), a model chromophore of green fluorescent protein ( GFP ) and of a positively charged neutral (N+)‐ HBDI chromophore model, were performed in gas phase with the resolution‐of‐identity algebraic diagrammatic construction through second‐order ( RI ‐ ADC (2)) method. The calculated absorption spectra in gas phase are composed of one band centered at 3.51 eV ( HBDI ), 2.50 eV ( HBDI − ) and 3.02 eV ((N+)‐ HBDI ) owing to the absorption of the first 1 ππ * transition. Band maxima are redshifted by ~0.1 eV with respect to the corresponding vertical energies. The COSMO ‐ RI ‐ ADC (2) calculations of the first vertical excitation energy of HBDI , HBDI − and (N+)‐ HBDI forms in polar solution including microsolvation simulate the observed solvent redshift for neutral HBDI and the solvent blueshift of the HBDI − and (N+)‐ HBDI forms. The state‐specific solvation approach applied to TDDFT calculations reproduced the experimental solvent shifts for the three HBDI forms, demonstrating a more accurate theoretical description as compared to the linear‐response TDDFT approach.