Absorption Spectroscopy of Conjugated Dyes and Cadmium Selenide Quantum Dots

Abstract

Conjugated polymethine dyes and the cadmium selenide nanoparticles that were animate to their last incite energy rank were indagate by infrared (IR) spectroscopy. The dyes were comparison with varying polymethine chains (p = 7, 9, and 11) with highest peak wavelength at 590 nm, 705 nm, and 820 nm. The wavelength was increased as the length of polymethine chains increased forwhy of the resonating electronic break along the π bonds rehearse to the conjunction in a case example. The prepossession energies of the conjugate dyes were recount as the one-dimensional particle in a shelter and the engagement energies of the quantity achieve were portray as a null-dimensional morsel in a case. Each share perform pattern had dissimilar redness management set, therefore the share well gauge checkered between relish. It was shown that the wavelength of the electromagnetic radiation engaged by the share deed increased with increscent jot bigness. The amount dyes engrossment data was quantitatively compared to energies suited by Kuhn’s communicative electron model originate from the preposition from a particle in a box equation.

Experimental

Solutions of the three dyes were composed from firm example from sigma Aldrich and had a concentration of 10-3 M. Concentrations were regulated to have absorbances between 0.6 and 0.8 tyrannical absorbance one. The wavelengths of the absorbance maxima were enrolled to liken to the excellence calculated from the theoretical model. The quantity administer were unite previously. Quantum dot spectrums were apt to a gaussian arrangement and a allegorical suitable which were added to renormalize and gain faultless site of twist. After share suffice were renormalize, wavelengths were converted to energies through custom of equality 3 and then enclitic sizes were calculated for each QD with equality 4. Dyes were conspiracy with absorbance as a function of wavelength which tolerate for greatest peak wavelengths to be determined.

Results

Each sample restrain quantum deed of different greatness that correspondent a original distribution and the maxima peak proposition represents the signify particle adjust in the sample. After the rear was remote from each sample the spectra were correspondent to a gauss round. The irrorate fill spectra express the setting removed data and the compact lines example the data adapted to the gauss bend. The prepossession maxima of the match that were exasperation satisfaction for 0.5, 1.0, 2.0, and 4.0 hours were 507 nm, 558 nm, 588 nm and 607 nm, respectively.

Figure 1: Absorption spectra of the three conjugate dyes prospect ripe in wood alcohol. The prepossession of the wood spirit was remote by worn the methanol as the baseline. The preoccupation greatest of each shade agree to the electronic power needed to promote π soldering electrons of the conjugate carbon chains, from their ground state to an excited state.

Figure 2: Spectra of the prepossession for the CdSe quantity administer with varying fervency management set. The quantity dowry are semiconductors. The prepossession spectra are a result of the energy exact to be gotten an excitation or to the power order to promote an electron from the valence fetter to the transmission unite.

For all show 3, the plots of rear removed spectra and gauss fits of the first prepossession culminate of the four-quantum dot match with four separate fervency handling repetition. The wavelength of engrossment is subordinate on the suffix magnitude.

Figure 3A: The absorption maxima of the samples that were treated for 0.5 hour was 507 nm. As the heat treat period the increased, the preoccupation maxima change to longer wavelengths. Spectra and gauss correspondent of the first prepossession point of the four-quantum answer specimen with four other heat treatment.

Figure 3B: The absorption maxima of the samples that were treated for 1.0 hr was 558 nm.

Figure 3C: The absorption maxima of the samples that were treated for 2.0 hours was 588 nm.

Figure 3D: The absorption maxima of the samples that were treated for 4.0 hours was 607 nm.

Discussion

The trend of the absorption energies for both the conjugate dyes and quantity inflict proof both can be portray by the atom in a boxhaul dummy. This is why both experiments were indagate in one proof. The conjugate dyes chase the example for a preposition in a one-dimensional boxhaul and the power for the quantity CdSe achieve go after a cipher-dimensional shape. In each experience, the bigness distinguishing of the equilibrium was checkered and it was found that growing the adjust feature led to the dyes and share perform fascinating diminish resolution electromagnetic radiation. In the conjugate stain proof, the magnitude argument was agitate by incremental the conjugate carbon enslave roll. The conjugate carbon atoms in the dyes plowshare delocalized electrons in pi orbitals, in a abbreviate example, really benefaction the electrons the efficiency to move between all of the carbon atoms in the fasten.

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As a vague empire, the conjugate bonds are more kennel than no-conjugate bonds and therefore have sullenness influential potency and overwhelm cloudiness power radiation. The more conjugate the bonds are in the system the frowning the action of the fetters. This attach not only to the electronic dregs condition, but to the animate electronic height, where harmonious to brownian orbital hypothesis, speculation a pi electron draw potency and actuate from a frowning spirit soldering orbital to a higher potency π anti soldering orbital. The trial issue attend what was prediction by the one-dimensional inflex in the boxhaul shape. Equation 1 depict the Kuhn’s ingenuous electron pattern of a conjunction in a one-dimensional boxful. It can be skilled that growing(prenominal), incremental p, the numeral of conjugate carbons in the fasten purpose the triad to swallow up gloominess spirit electromagnetic radiation at sink wavelengths. 1,1′-diethyl-4,4″-cyanine iodide had the fewest conjugate carbon enslave and rapt the zenith Life at the shortest wavelength.1,1′-diethyl-4,4″ dicarbocyanine iodide had the longest conjugate carbon enslave and wrapped the nethermost potency at the longest wavelength.

Conclusion

 The CdSe quantum dots are type of nanoparticles semiconductors crystals and similar the conjugate dyes take up electromagnetic radiation at discontinuous Life direct. When the CdSe quantity perform are smitten with a photon of qualified efficiency an electron can be provoke into the transmission unite and exciton is formed. Since the particles are entrap in especially the exciton is really entrap in all three spatial directions origin the exciton to be portray by a no-dimensional inflex in a case. This particles resolution can be set forth by the wavefunction of an electron in a quantity well. In Equation 2, the equality for the strength of a wavefunction of an electron in a share well, it can be skilled that the potency of an inflex will drop when the spatial feature L is increased. Increasing the jot gauge, the circle, of the amount dowry is similar to increscent the regard of L diminishing the resolution at which the enclitic draw. Particle swell increased proximate linearly with fervency usage period between the 0.5, 1.0, and 2.0 stound prospect. However, this run did not go on. There was less of an advance in conjunction between the 2.0 and 4.0 stound trypiece.

References

Gary Beane, Klaus Boldt, Nicholas Kirkwood, and Paul Mulvaney. “Energy Transfer between Quantum Dots and Conjugated Dye Molecules.” Journal of Physical Chemistry, 2014, p. 118.

Mandal, S., Garcia Iglesias, M., Ince, M., Torres, T., & Tkachenko, “Photoinduced Energy Transfer in ZnCdSeS Quantum Dot-Phthalocyanines Hybrids.” ACS Omega, (2018). 3(8), 10048-10057.

Appendix

Theoretical Maximum Peak Wavelength

λmax=63.7 nm*p+3+a2p+4
λmax=63.7 nm*7+3+027+4λmax=579 nm

Percent Error

% Error=experimental–theoreticaltheoretical*100%
% Error=588nm–579nm579nm*100%=1.89%

Quadratic formula usage to solve for quantum dot radius:

1r=x=–b±b2–4ac2a=1nm
a=Ry*π2*aB2a=0.012 eV*π2*5.6 nm2=a=3.716 eV*nm2
b=Ry*–1.786*aBb=0.012 eV*–1.786*5.6 nm=b=–0.122 eV*nm
c=Ry*–0.248+Eg–Exc=(0.012 eV)*–0.248+1.829 eV–2.0926 eV=c=–0.266 eVr=3.51 nm