Inheritance of Photochromic Properties of Nitro-Substituted and Halogenated Spiropyrans Containing the Pyrrolidino[60]fullerene

Abstract

The photophysical and isomerization properties of hybrid molecular compounds that consist of photochromic nitro-substituted and halogenated spiropyran derivatives bonded to the surface of the [60]fullerene cage through the pyrrolidine bridge were investigated using various functionals and basis sets of TD-DFT and semiempirical quantum-chemical approaches. The role of nπ* states formed by the lone pairs of substituents in changing of the electronic structure and photochromic properties of spiropyran derivatives was evaluated. The S(spiropyran) → intermediate nπ* states → S(merocyanine) channel for phototransformation of the hybrid compound containing a nitro-substituted spiropyran moiety was established and compared with similar systems of halogenated spiropyrans attached to the [60]fullerene bulk where photoinduced isomerization does not process due to high probability of internal conversion from the excited electronic state localized on the spiropyran fragment to the states of the pyrrolidino[60]fullerene.

Photocontrolled organic field effect transistors based on the fullerene C60 and spiropyran hybrid molecule

“…In view of the above and as a continuation of our research towards the preparation and studies of properties of hybrid molecules based on fullerenes and photochromic compounds aimed at the design of more efficient and promising organic electronic devices, [13][14][15][16][17][18] we have fabricated and investigated a photocontrolled OFET containing pyrrolidinofullerene 1 as the active layer ( Fig. 1a).…”

Photo-Transformation Trajectories of Nitro-Spiropyran in Hybrid Compounds with [60]Fullerene

“…An excitation of the spiropyrans leads to an unstable compound and a breaking of the ring-opening C spiro O bond, which prevents fluorescence relaxation (in particular to nSP). 20,24 (a) (c) The part of the compound most sensitive to configurational change in the excited states is the spiro unit at the intersection between the dihydropyrrole and dihydropyran motives (Figure 1).…”

“…intermediate n* states  S  (nMC) channel for photo-transformation of the corresponding hybrid compound. 20 This conclusion was based on an analysis of the electronic structure of equilibrated nSP and nMC conformers in the ground and excited electronic states. However, neither kinetic photoinduced excited-state trajectories of the C spiro O dissociation nor the s2m transformation were considered in previous work.…”

“…Second, the β dihedral angle was fixed to find a minimum energy barrier for the transformation between QSC and the final equilibrated n MC in the excited state. The PESs of the thermal , back-conversion to n SP was obtained by relaxing the oxygen-spiro distance in the electronic ground state.…”

“…|nπ(nSP,FCo)  state (E = 94 kcal/mol) through radiative processes. However, this is a very unlikely event as the oscillator strength for the transition between * and n* singlet states are almost forbidden due to their near different space symmetries.The competition between radiationless vibrational transitions at the intersection of the two excited states, a state intersection (SI) S |ππ,SI  S |nπ,SI at E = 99 kcal/mol, or even to a relaxed S |ππ,0 with E = 92 kcal/mol, and the process of C spiro −O bond cleavage in the predissociation phase of the photochromic conversion was recently proposed 20. Compared to other spiropyran derivatives, nSP has an additional channel through the n* state to provide the s2m conversion.…”