Synthesis And Properties Of D-A Type π-conjugated Organic Molecules

Donor-Acceptor π-conjugated organic molecules have been receivedconsiderable attention in many fields, especially in DSSCs, light-emitting diodes, twophoton absorption, organic field-effect transistors, sensor devices, and so on.Triphenylamine, phenothiazine, carbazole are electron-rich systems, which havestrong electron donating ability, good hole transport and electron transport properties.And their derivatives display good competitive power in the photovoltaic fields. Inaddition, dimesitylboron derivatives have wide applications in fluoride ion detection,OLED, two photon absorption and emission etc. So, herein, we mainly focus thesynthesis of a series of multifunctional donor-acceptor π-conjugated organicmolecules from triphenylamine, phenothiazine, carbazole, cyanoacrylic acid anddimesitylboron and the investigations of their photophysical, electrochemical andfluorescence sensing properties. And, some creative results have been obtained, whichwere outlined below:(1) Three new Y-shaped cyanoacrylic acid derivatives TT、TPand TC have beensynthesized by Heck and Knoevenagel reactions in good yields, and their donor partswere4-((E)-4-(diphenylamino)styryl)-N-(4-((E)-4-(diphenylamino)styryl)phenyl)-N-phenylaniline,4-((E)-2-(10-octyl-10H-phenothiazin-3-yl)vinyl)-N-(4-((E)-2-(10-octyl-10H-phenothiazin-3-yl)vinyl)phenyl)-N-phenylaniline,4-((E)-2-(9-octyl-9H-carbazol-3-yl)vinyl)-N-(4-((E)-2-(9-octyl-9H-carbazol-3-yl)vinyl)phenyl)-N-phenylaniline, respectively, and the acceptor parts were all cyanoacrylic acid. The three newdyes have been used in dyes sensitized solar cells successfully. It was found that theintroduction of Y-shaped π-conjugated systems to the body not only can broaden thespectrum absorption range and can effectively inhibit the aggregation of dyemolecules in the surface of titanium dioxide due to their large spatial structure, and which greatly improved the photovoltaic performance of dye-sensitized solar celldevices. The total photo-to-electrical conversion efficiency (η) of DSSCs based onthese three new dyes (TT、TP and TC) were5.12%,4.84%and3.63%under AM1.5irradiation (100mW/cm2), which were all higher than that of dye T (2.79%)bearing only one triphenylamine as the donor. And the η of DSSC based on dye TTshowed the best photovoltaic performance and the Jscand Vocvalues in the TT-basedDSSC are12.37mA/cm2and0.72V. In order to extend the absorption range of dye inthe visible light region, we increase the π-bridge conjugation length of dye TT. Wesynthesized three new organic dye molecules TT1, TT2and TT3, whose π-units werevinyl furan, vinyl thiophene and vinylbenzene. It was found that the introduction offuran and thiophene π-linkers to the dyes could tune the HOMO-LUMO level,increase the spectral response range. So they could showed higher IPCE andincrease the total photo-to-electrical conversion efficiency. As a consequence, thesolar cells based on dye with furan and thiophene linker exhibit6.10and5.92%conversion efficiency, respectively, which were higher than that of TT3(4.97%) andTT (5.12%). So, increasing the conjugation degree of dye molecules can broaden thespectrum absorption range, improve the open circuit voltage, and improve the deviceperformance of dye-sensitized solar cells. So, this work will be helpful for us todesign new good dyes.(2) Three new D-π-A dimesitylboron derivatives (PFTB、TFTB and TPTB)have been synthesized by Heck, Wittig and nucleophilic substitution reactions, wherethe acceptors were all dimesitylboron; the donor parts were phenothiazine,triphenylamine and triphenylamine-phenothiazine, respectively; and the bridge unitswere fluorene ethylene thiophene, fluorene ethylene thiophene and vinyl thiophene,respectively. It was found that the colors of these three compounds could change fromyellow to greenish yellow after being adding fluoride quickly, and it showed thesethree componds could selectively recognize fluoride anion by naked eyes. The threecompounds still could selectively recognize fluoride anion rapidly and efficiently inpresence of other anions Cl-, Br-, I-, OAc-, HSO-4, H2PO-4, which showed strong anti-interference ability. And it was found that the detection limits for F-were7.52×10-8molL-1（PFTB）、7.51×10-8molL-1（TFTB）and1.58×10-7molL-1（TPTB）.Moreover, it was found that they exhibited two photon absorption (TPA) ability, forexample, PFTB could emit strong green light under illumination by visible and nearIR light and the TPA cross sections of PFTB were1801GM at865nm in toluene.Upon addition of F-, the two-photon excited fluorescence emission band of PFTBblue-shifted from578nm to520nm upon adding F-, accompanied with the decreaseof TPA cross section. Therefore, PFTB can act as a TPA fluorescence probe fordetecting F-selectively.A new TPE-dimesitylboron derivative (TPETB) based on TPE was synthesizedby Stille reaction and nucleophilic substitution reaction, where the bridge unit wasthiophene. It was found that it showed good AIE property and it could emitblueish-green fluorescence in the solid with high fluorescence quantum yield0.40. Itis interesting that TPETB could selectively recognize fluoride anion by naked eyes.Upon addition of F-, the color of the solution of TPETB in DCM turned into colorlessfrom pale yellow accompanied with the decrease of fluorescence intensity. And, it wasfound that the detection limit for F-was1.67×10-8mol/L. This work provided us anew strategy to design two photon fluorescence probes.(3) Two π-conjugated D-π-A-π-D dendrimers (TBT and TBMT) bearing atriphenylamine moiety as dendrons, quinoxaline and2,3-dimethylquinoxaline as coreshave been synthesized through a convergent synthetic strategy, respectively. And theirphotophysical and electrochemical properties were also investigated. It was found thatthe two compounds could emit strong yellow light in toluene and their fluorescencequantum yields were0.52and0.66, respectively, according to rhodamine6G. Themaximum absorption and emission peaks in film were significantly red-shifted andcould emit strong red fluorescence in the film, which were good red emittingmaterials. The two compounds may be used in the OLED.