Small molecule-based photocrosslinkable fluorescent materials toward multilayered and high-resolution emissive patterning

Abstract

International audiencea Solution-processable green and red-emitting fluorophores possessing photopolymerizable acrylate units have been synthesized. Photocrosslinking was successfully performed in neat thin films at room temperature under low-dose UV irradiation at 365 nm. No further curing step was necessary to achieve insoluble emissive thin films displaying high optical quality. Up to 80% of the green emitting material processed as a non-doped thin film remained after photopolymerization. Despite competitive energy transfer occurring between the excited photoinitiator and the radiative excited state of red-emitting materials, up to 40% of the initial thickness could be achieved after development. The very low RMS roughness of the green and red photocrosslinked thin films after development (RMS o 0.7 nm) allowed us to fabricate multicolored stacks again with high optical quality (RMS roughness o 1.3 nm) after two cycles of irradiation and development involving successively red and green emitters. Resolved patterns as small as 600 nm in width could be obtained upon photolithography performed under an air atmosphere. High adhesion of the photocrosslinked materials on surfaces makes the resulting emissive thin films very promising for realizing complex emissive structures on flat or bend substrates as required in multiple applications such as optical data storage, organic lasers, organic light emitting diodes or counterfeiting

Microfluidic Assisted Flash Precipitation of Photocrosslinkable Fluorescent Organic Nanoparticles for Fine Size Tuning and Enhanced Photoinduced Processes

“…All nanoparticle dispersions displayed bright bluish-green emission, centered at 500 nm upon excitation in the UV absorption band composed of a shoulder at 375 nm and a maximum at 345 nm that are related to charge transfer from the triphenylamino center to the formyl and biphenyl moieties, respectively. [23] Interestingly, this emission maximum is quite similar to that reported for nondoped thin films fabricated by spin-coating a 1 wt. % dye solution in chloroform and subsequently vacuum-dried, [23] thereby indicating that local polarity effects originate from the dyes themselves, independently of the surrounding hydration shell.…”

“…Both fluorophores employed in these studies, ALD (bis(2-(acryloyloxy)ethyl) O,O'-((((4-formylphenyl)azanediyl)bis([1,1'-biphenyl]-4',4diyl))bis(ethane-1,1-diyl)) disuccinate) and VIN (bis(2-(acryloyloxy) ethyl) O,O'-((((4-(2,2-dicyanovinyl)phenyl)azanediyl)bis([1,1'-biphenyl]-4',4-diyl))bis(ethane-1,1-diyl)) disuccinate), were synthesized according to literature procedure. [23] Spectroscopic grade and inhibitor-free THF, used for all preparations and photophysical studies, and photocrosslinking respectively were purchased from Aldrich. Three ALD solutions in THF with varying concentrations (0.5, 1 and 2 wt.…”

“…In order to generate photocrosslinkable FONs out of small molecules following high impact-flow microfluidics, we resorted to push-pull structures ALD and VIN that had been designed to display both fluorescence and photocrosslinking properties in the solid state for solution-processed OLEDs (Figure 1). [23][24] Such compounds display large structural similarity and distinct emission ranges, namely greenish-blue for ALD and orange-red for VIN as a result of their aldehyde and dicyanovinylidenyl groups respectively, that will be exploited latter in the manuscript to fabricate color-tunable FONs.…”

“…In agreement with the increasing amount of compound VIN, an absorption band centered at 452 nm rose ( Figure 6A), typical of the lower charge transfer excited state calculated from TDDFT computations. [23] Given the absence of spectral overlap in the visible between the absorption spectra of the ALD blue and VIN red emitters and the match at 375 nm between a maximal absorption for ALD and a minimal absorption for VIN, the emission spectra were recorded upon excitation at 375 nm and 452 nm to distinguish the contribution of both dyes and assess the extent of energy transfer. For λ exc = 375 nm, the emission band centered at 500 nm was typical of pure FON ALD and dramatically shifted to 589 nm for FONs comprising only a 5 mol.…”

“…We here based our approach on the fact that ALD, processed as thin films, could undergo solid-state through a photoinitiated radical polymerization of its acrylate units. [23] In order to limit the action of oxygen acting as a radical scavenger, we privileged the well-documented thiol-ene reaction, highly compatible with water and ambient air and temperature conditions. [36] Pentaerythritoltetrakis(3-mercaptoprioionate) (PT-SH), containing four thiol units, was chosen as a crosslinker while 2,4-6-trimethylbenzoyl-diphenylphosphine (TPO) was retained as a hydrophobic photoinitiator (Figure 1).…”