Unspecified verticality of Franck-Condon transitions, absorption and emission spectra of cyanine dyes, and a classically inspired approximation

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The computed vertical energy, E v,a/f, from the equilibrium geometry of the initial electronic state is frequently considered as representative of the experimental excitation/emission energy, E abs/fl = hc/λ max. Application of the quantum mechanical version of the Franck-Condon principle does not involve precise specification of nuclear positions before, after, or during an electronic transition. Moreover, the duration of an electronic transition is not experimentally accessible in spectra with resolved vibrational structure. It is shown that computed vibronic spectra based on TDDFT methods and application of quantum mechanical FC analysis predict E abs = hc/λ max with a 10-fold improvement in accuracy compared to E v,a for nine cyanine dyes. It is argued that part of the reason for accuracy when this FC analysis is compared to experiment as opposed to E v,a/f is the unspecified verticality of transitions in the context of the quantum version of the FC principle. Classical FC transitions that preserve nuclear kinetic energy before and after an electronic transition were previously found to occur at a weighted average of final and initial electronic state molecular geometries known as the r-centroid. Inspired by this approach a qualitative method using computed vertical and adiabatic energies and the harmonic approximation is developed and applied yielding a 5-fold improvement in accuracy compared to E v,a. This improvement results from the dominance of low frequency vibronic transitions in the cyanine dye major band. The model gives insight into the nature of the redshift when qPCR dye EvaGreen is complexed to λDNA and is applicable to the low frequency band of similar non cyanine dyes such as curcumin. It is found that the computed vibronic cyanine dye spectra from time-dependent FC analysis at 0 K and 298 K show decreased intensity at higher temperature suggestive of increased intensity with restricted motion shown when cyanine dyes are used in biomedical imaging. A 2-layer ONIOM model of the DNA minor groove indicates restricted motion of the TC-1 dye excited state in this setting indicative of enhanced fluorescence.

Medienart:	E-Artikel

Erscheinungsjahr:	2020
Erschienen:	2020

Enthalten in:	Zur Gesamtaufnahme - volume:10
Enthalten in:	RSC advances - 10(2020), 70 vom: 23. Nov., Seite 43153-43167

Sprache:	Englisch

Beteiligte Personen:	Alia, Joseph D [VerfasserIn] Flack, Joseph A [VerfasserIn]

Links:	Volltext

Themen:	Journal Article

Anmerkungen:	Date Revised 16.07.2022 published: Electronic-eCollection Citation Status PubMed-not-MEDLINE

doi:	10.1039/d0ra06774a

funding:
Förderinstitution / Projekttitel:

PPN (Katalog-ID):	NLM340434678