Photomechanochromic vs. mechanochromic fluorescence of a unichromophoric bimodal molecular solid: multicolour fluorescence patterning

Abstract

The multicolour fluorescence responses to external mechanical forces vs. internal photomechanical stresses of a molecular solid are demonstrated and compared.

Alkyl Chain Length‐ and Polymorph‐Dependent Photomechanochromic Fluorescence of Anthracene Photodimerization in Molecular Crystals: Role of the Lattice Stiffness

“…Despite the observations of alkyl chain length-dependent crystal polymorphism, not all of the obtained crystalsw ere qualified for X-ray single-crystal structural analysis. Besides the previously reported Ya nd Gf orms of 1-C8, [9] the new crystal structures determined in this work are the Yf orms of 1-C9, 1-C10,a nd 1-C12,t he Gf orms of 1-C4, 1-C7,a nd 1-C9,a nd the Bf orm of 1-C16 (Table 1). Therefore, the following discussion on photodimerization activitya nd the associatedf luorochromism is mainly based on thesec ompounds.…”

“…Solvents for organic synthesis were reagent-or HPLC-grade, but for spectroscopy and quantum-yield measurement, they were all HPLC-grade. All new compounds were characterized by 1 Hand 13 CNMR and IR spectroscopy and mass spectrometry.C ompounds 1-C8 and 2-C8 have been reported, [9] and the syntheses of other 1-Cn and 2-Cn were carried out with the same protocols. The synthetic details are provided in the Supporting Information.…”

“…[1,[4][5][6][7][8] We recently observed an ew type of photomechanical effect that is ap henomenon at the molecular level (i.e.,l ocal photomechanical effects), in which the photomechanical stress perturbst he intermolecular interactions of the neighboring molecules that have not yet reacted, such that the fluorescencecolor of the crystals is changed. [9] More specifically,t he crystals of an anthracene-ethynylene-pentiptycene p-conjugated system containing a terminal octyloxy group (1-C8,S cheme1)s how excimer emission, but it is switched to either monomer (blueshifted) or super-dimer (redshifted) emission, depending on the crystal polymorph, with progressing [4+ +4] photodimerization of the anthracene groups.Wecalled it photomechanofluorochromism (PMFC) rather than photofluorochromism (PFC), because the latter referst ot he change of the fluorescence source from the reactantt ot he photoproduct insteado ff rom the initial to the perturbed reactant. The PMFC behaviori sreminiscent of ar elated fluorochromism caused by external mechanical stress such as grinding andc ompression,k nowna sm echanofluorochromism (MFC).…”

“…The conceptual differences among MFC, PMFC, and PFC are schematically shown in Figure 1. Unlike MFC, whichi sw ell demonstrated in the literature, [10][11][12][13][14] examples of PMFC or PFC are very rare, [9,15] The [4+ +4] photodimerization of anthracenea nd its derivatives plays ac ritical role in our current understanding of topo-chemistry andi nt he development of photomechanical crystalline materials.T he topochemical principle of "minimum atomic and molecular movement" formulatedb yS chmidt and Cohen in the 1960s offers ag eneral guideline for predicting the feasibility ands tereochemistry of a [ 2 + +2] or [4+ +4] photodimerization reactioni nacrystallines olid. [16] Crystale ngineering under this guideline for effective photoreactions continues to be an attractive subject in materials chemistry [17][18][19] and supramolecular photochemistry.…”

Mechanochromic and vapochromic fluorescence of a bulky π‐system: Alkyl chain‐length effects, triplex emission, and differential sensing of aniline vapors

“…Vapochromic luminescent materials are promising chemical sensors, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] because photoluminescence (fluorescence or phosphorescence) is a signal of inherently high sensitivity and the vapor-induced change of emission wavelength in the visible light region could be directly detected by naked eyes and/or analyzed ratiometrically at different wavelengths. Compared to phosphorescence, fluorescence signal has the advantage of lower susceptibility to quenching by ambient molecular oxygen; however, vapofluorochromic organic solids [11][12][13][14][15][16] are much less reported as compared with vapophosphorochromic organometallics and coordination compounds. [1][2][3][4][5][6][7][8][9][10] Since stimuliinduced fluorochromism of organic systems is generally based on the monomer-excimer or the monomer-exciplex switching, [17,18] strategies that promote such types of optical switching would facilitate the development of moleculebased vapochromic fluorescent sensors.…”