Optical Properties and Molecular Orientation of Aggregates in Langmuir–Blodgett Films of a Long-Chain Spiropyran

Abstract

The aggregate formation was studied for Langmuir–Blodgett films of a spiropyran 5Me-SP1822 (1′-octadecyl-3′,3′-dimethyl-5′-methyl-6-nitro-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2′-indoline]). Both a J-aggregate (λmax = 605 nm) and an H-aggregate (λmax = 493 nm) were formed, depending on the nature of the matrix molecule and the annealing temperature. The compound, having a substituent at the 5′-position, seems to prefer H-aggregation to J-aggregation by heat treatment at elevated temperatures. The molecular orientation in these aggregates was evaluated via analysis of the shifts in the first two absorption bands appearing after formation of the aggregates. Slip angles of 20—30° and 70—80° between the chromophore’s transition moment and the center-to-center line of the molecules, were found for the J- and H-aggregates, respectively, and a tilt angle of 20—30° between the chromophore’s plane and the film surface were obtained using the transition density model. These are in line with the results of Fourier-transform infrared (FT-IR) analysis.

Self‐Assembly of Photoresponsive Molecular Amphiphiles in Aqueous Media

“…Langmuir monolayers of photoresponsive amphiphiles containing azobenzene,s piropyran, stilbene,o vercrowded alkene,and dithienylethene units,show controlled reversible surface pressure,a nd tightly packed thin films of assembled structures can be obtained by the Langmuir-Blodgett method, which indicates significant prospects for optical devices and sensing applications. [96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115] Gibbs monolayers (absorption monolayers), composed of water-soluble amphiphiles directly distributed at the air-water interfaces without the use of organic solvents,s how tight correlations between assemblies in aqueous solution and at the air-water interface. In early studies of Gibbs monolayers of photoresponsive amphiphiles,s ome crucial equilibrium physical parameters, e.g.,e quilibrium surface tension and critical micelle concentration (CMC), were employed to reveal the self-assembly transformations at air-water interfaces and in solutions.…”

“…Langmuir monolayers, formed by insoluble or sparingly soluble amphiphiles, have attracted great interest due to the intrinsic properties facilitating the formation of well‐organized layered films. Langmuir monolayers of photoresponsive amphiphiles containing azobenzene, spiropyran, stilbene, overcrowded alkene, and dithienylethene units, show controlled reversible surface pressure, and tightly packed thin films of assembled structures can be obtained by the Langmuir–Blodgett method, which indicates significant prospects for optical devices and sensing applications [96–115] . Gibbs monolayers (absorption monolayers), composed of water‐soluble amphiphiles directly distributed at the air–water interfaces without the use of organic solvents, show tight correlations between assemblies in aqueous solution and at the air–water interface.…”

Mechanism of Peripheral Substituent Effects on Adsorption–Aggregation Behaviors of Cationic Porphyrin Dyes on Tungsten(VI) Oxide Nanocolloid Particles

“…Thereupon, we hypothesize the probable model for adsorption of the TPyP derivatives on the WO 3 colloid surface, as shown in Scheme 2. [51][52][53] Taking into account that the curvature radius R of WO 3 colloid particles nearly equals to 7.9 nm (from TEM image), we predicted the molecular area (per TPyP derivative) as follows: It is well-known that molecular aggregation drastically modifies the absorption characteristics (spectral shifts, band broadening, and sharpening) of the dyes.…”

J-aggregate Formation and Thermal Decay Kinetics of Photoinduced Merocyanine in Bilayer Membrane as a Function of the Mixing Ratio.

“…Photochromic reactions occurring within the molecular assemblies such as micelles, polymer films, and Langmuir-Blodgett multi-layers have attracted much attention with respect to practical applications as a possible recording medium for information storage and retrieval devices [1][2][3][4][5][6][7][8][9]. Among the many related subjects, extensive studies on the photochromism behavior of spiropyrans (SPs) in bilayer membranes as a simplified model of the initial process of biological vision systems have been reported by Seki and Ichimura [10][11][12][13][14][15] and Tomioka and Inagaki [16,17].…”