High-pressure study on intramolecular excimer formation of 1,3-di-1-pyrenylpropane in various solvents

Abstract

We have examined the viscosity effects of intramolecular excimer (IE) formation in 1,3-di-1-pyrenylpropane (DPP) at high pressures in various solvents. The formation is strongly and exclusively dependent on solvent viscosity, while it is insensitive to solvent polarity. The rates of the excimer formation estimated from fluorescence quantum yields are represented as a unique function of solvent viscosity. A hindered rotation model based on Kramers' theory was applied successfully. The more general results without specific interaction of solvent were obtained. The intrinsic activation energy (15-18 kJ/mol), the intrinsic activation volume (-2.5 cm3/mol), and the frequency for the top of the barrier of this IE formation were determined.Formation processes involving large-amplitude motion, such as intramolecular excimer (IE) formation in bichromophoric molecules in which bulky chromophores must twist with respect to the connecting bonds, should depend on the frictional forces exerted by solvents. For full understanding of these solvent effects, there are further questions to be answered. The first is whether the rates of formation are controlled exclusively by the viscosity of solvents; namely, whether the rates are equal at the same viscosity, independent of the means by which that viscosity value was produced, i.e., by changing the pressure, the temperature, or the solvent. The second is the question of what type of analytical formulation is possible for the viscosity dependence of the I E formation process and what type of model is applicable for describing the microscopic motions involved in the I E formation.We found in some bichromophoric compounds that the formation rates of their intramolecular excited states are really dependent on solvent viscosity.I4 As for the IE formation of 1,3-di-l-pyrenylpropane (DPP), Thistlethwaite et aL5 reported that it was not dependent on solvent viscosity, while Zachariasse et a1.6 argued against it. Thereafter, Offen et al.' reported a viscosity dependence that is inversely proportional to solvent viscosity, indicating a diffusion-controlled collision process. In our previous paper, we suggested from the study at high pressures8 that this formation is absolutely dependent on solvent viscosity and proposed that the hydrodynamic model of hindered rotation based on Kramers' theory may be applicable to the viscosity dependence.In most studies on the influence of solvent viscosity, a series of homologous solvent^^*^^ or mixed have been used to achieve viscosity variation. A possible problem in these approaches is that there may exist large local variations in the solvent shell interactions with the aromatic chromophores. Specific and/or steric interactions between solvent molecules and aromatic chromophores should affect the rotational transformation process and the stability of the excimer. The application of high hydrostatic pressure, on the other hand, makes it possible to minimize this problem. It achieves a large amount of continuous variation (1) Hara, K.; Arase, T.; Osugi, J...

Hydrostatic Pressure on Toroidal Interaction and Propeller Chirality of Hexaarylbenzenes: Explicit Solvent Effects on Differential Volumes in Methylcyclohexane and Hexane

“…The effect of hydrostatic pressure has been extensively utilized for elucidating the mechanism of bimolecular reactions such as ground‐state host–guest complexation and excited‐state exciplex formation, where relatively larger volume changes are observed . The pressure effect was also noted in conformational changes of 9,9′‐bianthryl and 4‐[4‐(dimethylamino)phenyl]pyridine .…”

Cyclophane‐Based Fluorescence Tuning Induced by Hydrostatic Pressure Changes

“…Mechanical stimuli can vary photoluminescence properties of organic materials in solution and/or solid states . Mechanoresponsive organic compounds are promising candidates of indicator of applied force, optical data storage and mechano‐bioimaging probes for living cells.…”

“…Mechanoresponsive organic compounds are promising candidates of indicator of applied force, optical data storage and mechano‐bioimaging probes for living cells. Simple and basic studies on homogeneous solutions of various fluorophores under hydrostatic pressure as one of mechanical forces have been long‐term scientific subjects . In general, photoluminescence intensities of fluorophores in organic solvents augment under elevated pressure due to increasing viscosity of solvents used, and sometimes follow the Förster‐Hoffmann equation ,.…”

“…A pressure-induced enhancement of the formation of an intramolecular p-stacked conformation is proposed to be responsible.Mechanical stimuli can vary photoluminescence properties of organic materials in solution and/or solid states. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Mechanoresponsive organic compounds are promising candidates of indicator of applied force, optical data storage and mechano-bioimaging probes for living cells. Simple and basic studies on homogeneous solutions of various fluorophores under hydrostatic pressure as one of mechanical forces have been long-term scientific subjects.…”

High-Pressure Studies on the Excited-State Intramolecular Charge Transfer of 4-(N,N-Dimethylamino)triphenylphosphine in Alcohols

“…[2][3][4][5] Contrary to the early expectation, 3 it has recently been reported that no simple correlation between the TICT-state formation rate and solvent viscosity has been observed for the case of DMABN in a series of polar solvents with different viscosity. 6,7 By using a high-pressure method, we have been studying the influence of solvent viscosity on various barrier crossing processes involving large amplitude twisting conformational changes due to bulky aromatic groups such as TICT-state formation, 8,9 intramolecular excimer formation, 10 and photoisomerization. 11,12 In particular, the observation of a weak dependence of the barrier crossing rate on solvent viscosity has been discussed.…”