First-Principles Molecular Dynamics Study of a Photochromic Molecular Crystal

Abstract

We present first-principles calculations for the thermal reaction in the photochromic molecular crystals of 2-(2′,4′-dinitrobenzyl)-pyridine (DNBP). Under irradiation this dye molecule undergoes a characteristic change of color as a result of an intramolecular proton-transfer reaction. By simulating the thermal reaction with first-principles molecular dynamics, we show that during the thermal proton transfer a hydrogen bond from the o-nitro group to the migrating proton is formed intermediately, which serves as a "bridge" between the educt and product forms. Furthermore, we present the experimentally not accessible structures of the crystalline photoisomers. On the basis of our results we conclude that photoisomerization is possible in the crystalline phase. This property is of elementary interest for technical applications of this system.

First-principles study of salicylideneaniline molecular crystals: Tautomerization reaction involving intermolecular hydrogen bonds

“…Hence, trying to optimize the cell constants for the soft lattice of the molecular crystal would probably yield meaningless results, as mentioned in Ref. 12. For the crystals, we located the local minima only, since the determination of the global minimum would have been excessive for the purpose of the present study.…”

“…Since there have been few ab initio studies on photochromic molecular crystals, 12 the present study is expected as a useful exemplar of density-functional theory to the molecular solid. The effect of the molecular packing is discussed from the energetics of the two forms, by comparing with the gasphase cases.…”

Ab Initio Molecular Dynamics Investigation of the Formyl Cation in the Superacid SbF5/HF

“…[18][19][20][21] The CPMD DFT scheme is particularly suited to condensedphase simulations employed here. Indeed, the CPMD method has already been used to study chemical reactions, [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and it has been shown to be an excellent tool to fully understand the chemical kinetics at a microscopic level. However, the majority of the studies of chemical reactivity carried out so far using DFT seem to indicate that the reaction barrier heights are underestimated (see, for example, refs 39 and 40).…”

Packing-dependent photochromism: the case of photoinduced intramolecular proton transfer in 6-(2′,4′-dinitrobenzyl)-2,2′-bipyridine

“…However, the structural results (Naumov et al, 2002) have indicated that the nitro group assists the proton transfer in NBPs. In addition, the theoretical results (Frank et al, 1996(Frank et al, , 1999 have shown that the involvement of the nitro group is important for the proton transfer in the ground-state thermal back-reaction NH A CH. On the basis of the results accumulated, it can be suggested that the photochromic activity of solid NBPs depends on the rotational freedom of the orthonitro group.…”