Morphological Characterization of H Aggregates in Langmuir−Blodgett Films of Pyridinium−Dicyanomethanide Dyes

Abstract

We investigated the aggregation of the pyridinium-dicyanomethanide dye 4-[5-(dicyanomethanido)-thien-2-yl]-N-(n-hexadecyl)pyridinium (C16H33-PDCNT), in transferred films obtained with the LangmuirBlodgett (LB) technique; this behavior is an example for the formation of H* aggregates, which show strongly blue-shifted and sharp electronic absorption bands. Surface pressure-area isotherms are reported at T ) 291 K. LB films were investigated by UV-vis spectroscopy and optical and atomic force microscopy in order to obtain information about the molecular structure of the aggregates. The molecule strongly absorbs in the visible region because of a charge-transfer band; the sharp peak at 422 nm is attributed to the formation of H* aggregates.

Interrupted-Growth Studies of the Self-Assembly of Intrinsically Acentric Siloxane-Derived Monolayers

“…12, [52][53][54]56 The absence of hypsochromic shifts in the present films argues against centrosymmetric H-type chromophore aggregation, which is known to suppress the second-order nonlinear optical responses in certain Langmuir-Blodgett film structures. 10,17 Figure 3 shows the deposition kinetics monitored by transmission second-harmonic generation measurements at λ 0 ) 1064 nm, which is a sensitive technique for monitoring thin film formation. 6,96,98 The second-harmonic 532-nm light output intensity, I 2ω , reaches a maximum after ∼6.5 h in good agreement with the advancing aqueous CA and optical absorption data.…”

“…[1][2][3][4][5][6][7][8][9][10][11] Organic device-quality functional thin films remain relatively rare despite the tremendous recent progress in this field. [12][13][14][15] Langmuir-Blodgett, 16,17 covalent molecular self-assembly, [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] bipolar amphiphiles and polyelectrolytes, 33 metal-coordination, [34][35][36][37][38][39][40][41][42][43][44][45] and related film transfer techniques 46 layer films, which can be grown on substrates such as silicon, indium-tin oxide-coated glass, and gold. We recently developed an efficient "one-pot" layer-by-layer assembly method for the formation of robust intrinsically acentric siloxane-based superlattices, as shown in Scheme 1.…”

“…Formation of organized organic materials with controllable electronic, optical, and electrooptical properties is a formidable and complex task. − Organic device-quality functional thin films remain relatively rare despite the tremendous recent progress in this field. − Langmuir−Blodgett, , covalent molecular self-assembly, − bipolar amphiphiles and polyelectrolytes, metal-coordination, − and related film transfer techniques 46 have been used to integrate various functional molecules in ordered multilayer films, which can be grown on substrates such as silicon, indium−tin oxide-coated glass, and gold. We recently developed an efficient “one-pot” layer-by-layer assembly method for the formation of robust intrinsically acentric siloxane-based superlattices, as shown in Scheme . − This straightforward synthetic approach is amendable to automation and involves two alternating solution deposition steps.…”

Adsorption Morphology, Light Absorption, and Sensitization Yields for Squaraine Dyes on SnS2Surfaces

“…Scanning tunneling microscopy (STM) has been applied to show molecular ordering of vacuum-deposited phthalocyanines − and perylene derivatives , on copper, gold, graphite, MoS 2 , and silicon surfaces. Cyanine dye J- and H-aggregates were also imaged by STM. − Atomic force microscopy (AFM) has also been used to investigate phthalocyanine films, cyanine dye J-aggregates, − and other organic dye aggregates. − For example, several nanometer thick leaf-like structures of pseudoisocyanine J-aggregates at the mica/water interface have been recently reported. − However, direct confirmation of the relationship between the morphologies of the dyes on the semiconductor surface and their photosensitizing properties has not been explored. The only study to correlate AFM morphologies, light absorption, and photocurrent spectra was reported for vacuum deposited phthalocyanines on TiO 2 single crystals; however, this study was mostly concerned with thick dye layers and the absorption spectra were recorded on glass slides rather than the actual sensitized substrates …”

“…[33][34][35][36] Atomic force microscopy (AFM) has also been used to investigate phthalocyanine films, 37 cyanine dye J-aggregates, [38][39][40][41][42][43] and other organic dye aggregates. [44][45][46][47] For example, several nanometer thick leaf-like structures of pseudoisocyanine J-aggregates at the mica/water interface have been recently reported. [41][42][43] However, direct confirmation of the relationship between the morphologies of the dyes on the semiconductor surface and their photosensitizing properties has not been explored.…”