Energetic and structural properties of different conformations of merocyanine and its protonated forms

Abstract

We investigate the conformational stabilities, dipole moments, bond lengths and partial charges of photo-sensitive spiropyran (1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitro-spiro[2H-1-benzopyran-2,2′-[2H]indole]) after its photo-switching to the open form conformers, merocyanine and its protonated counterparts. Two approaches, an ab initio Hartree-Fock method supplemented by the Møller-Plesset second-order perturbation theory and density functional theory under B3LYP parameterization, are employed with extended basis sets to examine the energetic ordering of the conformers in vacuum and in an aqueous environment. The influence of the solvent on the conformers is demonstrated by the notable changes in the structural and electrostatic properties.

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental–Theoretical Approach to Photophysical Properties and Self-Assembly

“…The geometry optimization of SP and MC is performed in a gas phase using the B3LYP/DGDZVP basis set with a tight self-consistent field convergence threshold. This functional is widely and successfully employed in studies of spiropyran-containing molecules [16,17,58,[68][69][70][71]. Next, the ground state geometries are optimized by applying the integral equation formalism variant of the polarizable continuum model (IEFPCM) to simulate the solvent environment [75].…”

“…The spiropyran in the conventional SP/MC pairs is commonly more favorable state [43,58,61,70,90]. Under UV light it converts to the thermodynamically less stable state (MC) which is more deeply colored form, and similar systems are called positive photochromic systems [94].…”

“…This property has been calculated for the optimized geometries in implicit water. The analysis of the ESP surfaces is a common approach to describe the ring-opening reaction of spiropyrans [79,98], to calculate the group charges accumulated on the acceptor and donor groups of the MC form as useful indicators to get insight into the charge separated state of the molecule [67,69], to shed light on the polarity of the protonated MC forms upon hydrolysis [70], for studying crystal packings of various spiropyrans [93]. The mentioned properties are assuredly important, but here we would like to emphasize that the charge redistribution appears also as a decisive factor of hydrophobicity change upon light stimulus, that has been anticipated in experiments [27,30,44].…”

“…Theoretical studies published so far include quantum chemical description of the photoinduced ring-opening reaction of spiropyrans bearing various substituents [58][59][60][61][62][63][64][65][66], classical, semiclassical and ab initio calculations of the hydration mechanisms and the water shells around spiropyran and merocyanine, as well as MC protonated forms [58,[67][68][69][70], and theoretical characterizations of the optical properties [71]. To the best of our knowledge, there is only a few papers devoted to the theory and modeling of the SP/MC amphiphiles.…”

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental–Theoretical Approach to Photophysical Properties and Self-Assembly

“…Theoretical studies published so far include quantum chemical description of the photoinduced ring-opening reaction of spiropyrans bearing various substituents [ 49 , 50 , 51 , 52 , 53 , 54 , 55 ], classical, semiclassical and ab initio calculations of the hydration mechanisms and the water shells around spiropyran and merocyanine, as well as MC protonated forms [ 49 , 56 , 57 , 58 , 59 ], and theoretical characterizations of the optical properties [ 60 ]. To the best of our knowledge, there are only a few papers devoted to the theory and modeling of the SP/MC amphiphiles.…”