How do structural factors determine the linear and non-linear optical properties of fluorene-containing quadrupolar fluorophores? A theoretical answer

Abstract

A large series of push-push and pull-pull quadrupolar fluorophore derivatives with conjugated rods made from arylene-vinylene (PV) or arylene–ethynylene (PE) building blocks, bearing different electron-releasing or electron-withdrawing end-groups was theoretically...

Linear and Nonlinear Optical Properties of Quadrupolar Bithiophenes and Cyclopentadithiophenes as Fluorescent Oxygen Photosensitizers

“…This result can be traced back to the structure of the cyclopentadithiophene spacer and not to the number of effective electrons (N eff ), which remains constant for 1a and 2a (27.0) and for 1b and 2b (28.1) [34]. Of the cyclopentadithiophene derivatives 2a,b, the better σ 2 value is obtained for 2b, which features electron-withdrawing groups at the periphery, in combination with the increased electron-richness of the central core proceeding from 1a,b to 2a,b, and as supported by the DFT calculations (see Section 2.3) [28].…”

“…From the exclusion rule operative for centrosymmetric compounds, this second singlet excited state (S 2 ) populated by 2PA is, in principle, 1PA-forbidden, and should not be observed in the 1PA spectra (although a weak shoulder can still be observed in 1PA), explaining the apparent shift between the 1PA and 2PA peaks. Interestingly, this model also seems to apply to 2a,b which are not centrosymmetric (C 2v symmetry with ideal conformations), although they possess a significant quadrupolar character along their long axis, similar to 3a,b [28,36]. The shoulder on the low energy side of the first 2PA absorption of 1a,b and 2a,b corresponds to population of the lowest (u-type) excited state, a transition in principle 2PA-forbidden under strict centrosymmetry, with the 2PA cross-sections of ca.…”

“…Such calculations are also routinely used to determine the key excited states in these processes [27]. Despite the simplicity of quadrupolar model compounds such as 1a,b and 2a,b, they have never been experimentally studied (to the best of our knowledge), while only 2a was briefly modelled by DFT and compared to 3a at the same level of theory [28]. According to these theoretical results, the cyclopentadithiophene derivative 2a should be a better Despite the simplicity of quadrupolar model compounds such as 1a,b and 2a,b, they have never been experimentally studied (to the best of our knowledge), while only 2a was briefly modelled by DFT and compared to 3a at the same level of theory [28].…”

“…Despite the simplicity of quadrupolar model compounds such as 1a,b and 2a,b, they have never been experimentally studied (to the best of our knowledge), while only 2a was briefly modelled by DFT and compared to 3a at the same level of theory [28]. According to these theoretical results, the cyclopentadithiophene derivative 2a should be a better Despite the simplicity of quadrupolar model compounds such as 1a,b and 2a,b, they have never been experimentally studied (to the best of our knowledge), while only 2a was briefly modelled by DFT and compared to 3a at the same level of theory [28]. According to these theoretical results, the cyclopentadithiophene derivative 2a should be a better two-photon absorber than 3a, pointing toward an appealing potential for cyclopentadithiophenes as a promising class of two-photon fluorescent dyes.…”

“…We herein report (i) their synthesis and characterization and (ii) the experimental determination and computational modelling of their one-and two-photon absorption, emission and oxygen photosensitization behavior before (iii) briefly discussing their potential for bio-oriented uses, as well as (iv) the role played by the sulfur atoms on the optical properties of interest. The data presently obtained for 1a,b and 2a,b are analyzed and contrasted with the experimental [24,25] and computational [28] data available for 3a,b and 3b .…”