Infrared study on order-disorder transitions in Langmuir-Blodgett films of 2-dodecyl-, 2-pentadecyl-, and 2-octadecyl-7,7,8,8-tetracyanoquinodimethane

Dependences of Thermal Behaviors on the Number of Layers in Langmuir−Blodgett Films of 2-Octadecyl-7,7,8,8-tetracyanoquinodimethane. 1. Order−Disorder Transitions in the Films Investigated by Ultraviolet−Visible and Infrared Spectroscopies

“…The results for these frequency shifts, together with those for the half-widths and intensities in the same temperature range, indicate that the chain melting temperature rises and approaches the bulk melting point (127°C 19 ) with the number of layers. Probably, the thermal stability of the LB films of octadecyl-TCNQ increases with the number of layers.…”

“…[13][14][15][16][17][18] To the best of our knowledge, investigations on the thermal behavior of LB films built up from functional organic materials are still very limited. Recently, our group investigated the thermal behaviors of LB films of 2-dodecyl-7,7,8,8-tetracyanoquinodimethane (dodecyl-TCNQ), 2-pentadecyl-7,7,8,8-tetracyanoquinodimethane (pentadecyl-TCNQ), 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ), 19 and 2-(4′-(dioctadecylamino)phenylazo)-N-methylbenzothiazolium perchlorate by using IR spectroscopy. 20 The following conclusions could be reached in the IR study on the order-disorder transitions in LB films of the three kinds of alkyl-TCNQ: 19 (i) the order-disorder transition in the LB film of octadecyl-TCNQ with the longer even-numbered hydrocarbon chain occurs at a higher temperature than that in the LB film of dodecyl-TCNQ with the shorter even-numbered hydrocarbon chain, but the LB film of pentadecyl-TCNQ with the odd-numbered hydrocarbon chain shows a transition temperature similar to the LB film of dodecyl-TCNQ; (ii) below the transition temperature a pretransitional disordering of the hydrocarbon chain takes place for all the LB films; (iii) the mobility of the hydrocarbon chains increases in concert with the progress of disordering; (iv) the order-disorder transition in the LB film of octadecyl-TCNQ is nearly reversible below 130°C.…”

Thermal Behavior of Mixed-Stack Charge Transfer Films of 2-Octadecyl-7,7,8,8-tetracyanoquinodimethane and 3,3‘,5,5‘-Tetramethylbenzidine Prepared by the Langmuir−Blodgett Technique and Donor Doping. 1. Dependence of Thermal Behavior on the Number of Layers Studied by Ultraviolet−Visible−Near Infrared and Infrared Spectroscopies

“…Our previous study on thermal behavior of LB films of octadecyl-TCNQ revealed that the band at 2216 cm -1 corresponds to a CtN stretching mode of the TCNQ chromophore in the melted state of the LB films. 22,24 Therefore, the band shift from 2208 to 2216 cm -1 indicates that octadecyl-TCNQ molecules change from the state of the CT complex to the neutral melted state.…”

Substitution controlled molecular orientation and nanostructure in the Langmuir–Blodgett films of a series of amphiphilic naphthylidene-containing Schiff base derivatives

“…It is well known that appearances of the CH 2 antisymmetric and symmetric stretching bands at lower wavenumbers (ca. 2918 and 2848 cm −1 , respectively) indicate a highly ordered and well-organized arrangement of the hydrocarbon chains, while their appearances at higher wavenumbers are indicative of the increase in conformational disorder in the hydrocarbon chains [32][33][34][35]. In present case, the vibration position suggested the alkyl chain kept basically in an ordered arrangement.…”