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Anthony, Savarimuthu Philip,Cho, Won Joon,Lee, Jeong In,Kim, Jin Kon Royal Society of Chemistry 2009 Journal of materials chemistry Vol.19 No.2
<P>Narrow band gap PbS and PbSe semiconductor nanocrystals were prepared in the poly(4-vinyl pyridine) core of self assembled polystyrene-<I>block</I>-poly(4-vinyl pyridine) copolymer micelles in toluene at room temperature, and characterized by high resolution-transmission electron microscopy and X-ray diffractograms. Optical absorption and photoluminescence (PL) studies of the nanocrystals showed the quantized phenomena. The PL intensity of the PbSe nanocrystals was strongly enhanced, with a slight red shift in the peak position, by treating with aqueous Na<SUB>2</SUB>S solution. Interestingly, the inclusion of ZnS amorphous nanoparticles into the P4VP/PbSe core leads to a large red shift in the peak position, which covers the technologically important range (1.3 to 1.55 µm), with strong enhancement of the emission intensity. We fabricated a monolayer thin film of PbSe nanocrystals by spin coating on a silicon wafer, and it showed similar PL behavior to that in solution.</P> <P>Graphic Abstract</P><P>Narrow band gap PbS and PbSe semiconductor nanocrystals were prepared in the poly(4-vinyl pyridine) core of self assembled polystyrene-<I>block</I>-poly(4-vinyl pyridine) copolymer micelles in toluene at room temperature. Photoluminescence properties were investigated and 2-D nano-arrays were fabricated. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b814157f'> </P>
Gayathri, Parthasarathy,Hariharan, Palamarneri Sivaraman,Moon, Dohyun,Anthony, Savarimuthu Philip Elsevier 2019 Journal of luminescence Vol.211 No.-
<P><B>Abstract</B></P> <P>Aggregation enhanced emissive (AEE) triphenylamine-phenylacetonitrile based donor-accepter compounds showed alkoxy chain length dependent solid state fluorescence efficiency and stimuli induced off-on fluorescence switching. Molecular conformational and packing differences lead to fluorescence tuning between 480 and 530 nm. The compounds exhibited off-on mechanofluorochromism upon crushing and heating. Interestingly, all compounds produced stable non-fluorescent melt that was converted to strongly fluorescent solids upon crystallization. The high-contrast off-on crystallization induced fluorescence switching has been used to demonstrate rewritable fluorescence platform. Single crystal structural analysis, powder X-ray diffraction and differential scanning calorimetry have been performed to understand the mechanism of fluorescence switching.</P> <P><B>Graphical abstract</B></P> <P>Crystallization induced fluorescence switching of alkoxy chain substituted triphenylamine smart fluorophores have been used to demonstrate rewritable fluorescent platform.</P> <P>[DISPLAY OMISSION]</P>
Hariharan, P. S.,Venkataramanan, N. S.,Moon, Dohyun,Anthony, Savarimuthu Philip American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.17
<P>A triphenylamine-based fluorophore, 4-((4-methoxyphenyl)(phenyl)amino)benzaldehyde (<B>1</B>), exhibits external-stimuli-responsive self-reversible solid-state fluorescence switching, tunable fluorescence, and a rare phenomenon of temperature-dependent fluorescence. Mechanically grinding a crystalline powder of <B>1</B> converts the blue fluorescence (λ<SUB>max</SUB> = 457 nm) to green (λ<SUB>max</SUB> = 502 nm), but blue fluorescence robustly self-recovers within 8 min. X-ray analysis and theoretical studies suggest that the change from a highly twisted molecular conformation and crystalline form into an amorphous phase with more planar conformation is responsible for the fluorescence switching. Self-reversible fluorescence switching did not show a significant change in fluorescence for several cycles of measurement. Interestingly, <B>1</B> in toluene showed a rare phenomenon of fluorescence enhancement with increasing temperature via activating more vibrational bands that lead to stronger twisted intramolecular charge-transfer (TICT) emissions. Morphological-change-mediated fluorescence tuning has also been demonstrated by fabricating nanoparticles of <B>1</B>. The conversion of highly polydispersed, featureless, different-shaped nanoparticles into nearly uniformly sized spherical nanoparticles (20–25 nm) converts green (λ<SUB>max</SUB> = 502 nm) to blue fluorescence (λ<SUB>max</SUB> = 478 nm). The self-reversible multi-stimuli-responsive fluorescence switching and polymorphism and nanofabrication-mediated fluorescence tuning suggest its potential application in sensors, particularly for fluorescent thermometers.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-17/acs.jpcc.5b00310/production/images/medium/jp-2015-00310a_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b00310'>ACS Electronic Supporting Info</A></P>
Hariharan, Palamarneri Sivaraman,Mothi, Ebrahim M.,Moon, Dohyun,Anthony, Savarimuthu Philip American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.48
<P>Halochromic isoquinoline attached mechanochromic triphenylamine, N-phenyl-N-(4-(quinolin-2-yl)phenyl)benzenamine (PQPBA) and tris (4-(quinolin-2-yl)phenyl) amine (TQPA), smart fluorescent materials exhibit thermo/mechanochromism and tunable solid state fluorescence and their unusual halochromic response in PMMA matrix have been used for fabricating rewritable and self erasable fluorescent platforms. PQPBA and TQPA showed strong fluorescence in solution (Phi(f) = 0.9290 (PQPBA) and 0.9160 (TQPA)) and moderate solid state fluorescence (Phi(f) = 20 (PQPBA) and 17% (TQPA). Interestingly, they exhibited a rare temperature (0-100 degrees C) dependent positive fluorescence enhancement via activating radiative vibrational transition. The deaggregation of PQPBA and TQPA in PMMA polymer matrix lead to the enhancement of fluorescence intensity strongly and fabricated strong blue fluorescent thin films (Phi(f)=58% (PQPBA) and 54% (TQPA). The halochromic isoquinoline has been exploited for demonstrating reversible off-on fluorescence switching by acid (TFA (trifluoroacetic acid)/HCl) and base (NH3) treatment in both solids as well as PMMA thin films. Importantly, rewritable and self-erasable fluorescent platform has been achieved by make use of unusual fluorescence responses of PQPBA/TQPA with TFA/HCl after exposing NH3. Single crystal and powder X-ray diffraction (PXRD) studies provided the insight on the solid-state fluorescence and external stimuli-induced fluorescence changes.</P>
Hariharan, Palamarneri Sivaraman,Prasad, Viki Kumar,Nandi, Surajit,Anoop, Anakuthil,Moon, Dohyun,Anthony, Savarimuthu Philip The American Chemical Society 2017 CRYSTAL GROWTH AND DESIGN Vol.17 No.1
<P>Triphenylamine (TPA), a propeller-shaped optoelectronic molecule, has been used to generate stimuli-responsive smart fluorescent organic materials and correlate the effect of subtle structural changes on the molecular packing and mechanochromic fluorescence (MCF). The substituent (OCH3) position in the TPA phenyl ring and acceptors (malononitrile, cyanoacetamide, cyanoacetic acid, ethyl cyanoacetate, and diethylmalonate) strongly influenced the solid state and mechanochromic fluorescence as well as the molecular packing. The structure-property studies revealed that (i) TPA derivatives without the OCH3 substituent exhibit strong fluorescence (Phi(f) = 85% (TCAAD-1, 55% (TDEM)), (ii) higher dihedral angle (tau) between donor (aminophenyl) and acceptor lead to weak/non fluorescent material, (iii) substituent at the ortho position to acceptor increased the dihedral angle (tau = 26.49 (TCAAD-2), tau = 27.14 (TDMM)), and (iv) the increase of alkyl groups produced self-reversible high contrast off-on fluorescence switching materials (TDEM). Powder X-ray diffraction studies indicate that stimuli induced reversible phase-transformation from crystalline to amorphous and vice versa was responsible for fluorescence switching. The computational studies also supported that OCH3 substitution at ortho to acceptor increased the dihedral angle and optical band gap. Thus, the present studies provide a structural insight for designing TPA based organic molecules for developing new smart organic materials.</P>
Kundu, Anu,Karthikeyan, Subramanian,Sagara, Yoshimitsu,Moon, Dohyun,Anthony, Savarimuthu Philip The Royal Society of Chemistry 2018 Physical Chemistry Chemical Physics Vol.20 No.43
<P>Molecular photoswitching, light induced reversible color/fluorescence modulation, has mostly been realized in organic molecules <I>via E</I>/<I>Z</I> isomerization of azobenzenes and stilbenes and ring opening/closing reactions of spiropyrans and diarylethenes. We report here new fluorescent molecular photoswitches based on triphenylamine (TPA)-imidazole derivatives, <I>N</I>-phenyl-<I>N</I>-(4-(1,4,5-triphenyl-1<I>H</I>-imidazol-2-yl)phenyl)benzenamine (NTPB) and <I>N</I>-phenyl-<I>N</I>-(4-(1-phenyl-1<I>H</I>-phenanthro[9,10-<I>d</I>]imidazol-2-yl)phenyl)benzenamine (NPPB), that exhibited light induced reversible fluorescence switching <I>via</I> conformational change from a twisted molecular structure to more planar. NTPB and NPPB in CHCl3 showed red shift of absorption and fluorescence upon UV light irradiation whereas white light exposure reversed both absorption as well as fluorescence. The role of the TPA-imidazole twisted molecular structure in photoswitching was established based on structure property, computational and photophysical studies. The isobestic point observed in time dependent fluorescence change under UV light irradiation clearly demonstrated the presence of two different conformational isomers. Interestingly, polymorphism and torsion angle (<I>τ</I>) dependent fluorescence of NTPB and NPPB in the solid state also supported the role of the twisted molecular structure of TPA-imidazole in fluorescence switching/tuning. Interestingly, NTPB showed fluorescence photoswitching in the solid state also whereas rigid phenanthrene based NPPB did not show fluorescence photoswitching. Thus the present studies provide structural insight for designing a new type of fluorescent organic molecular photoswitches based on conformational modulation that could be of potential interest in optoelectronic devices.</P>