Role of the Oxyallyl Substructure in the Near Infrared (NIR) Absorption in Symmetrical Dye Derivatives:  A Computational Study

Abstract

It is well-known from experimental studies that the oxyallyl-substructure-based squarylium and croconium dyes absorb in the NIR region of the spectrum. Recently, another dye has been reported (J. Am. Chem. Soc. 2003, 125, 348) which contains the same basic chromophore, but the absorption is red-shifted by at least 300 nm compared to the former dyes and is observed near 1100 nm. To analyze the reasons behind the large red shift, in this work we have carried out symmetry-adapted cluster-configuration interaction (SAC-CI) studies on some of these NIR dyes which contain the oxyallyl substructure. From this study, contrary to the earlier reports, it is seen that the donor groups do not seem to play a major role in the red-shift of the absorption. On the other hand, on the basis of the results of the high-level calculations carried out here and using qualitative molecular orbital theory, it is observed that the orbital interactions play a key role in the red shift. Finally, design principles for the oxyallyl-substructure-based NIR dyes are suggested.

Near infrared absorbing benzobis(thiadiazole) derivatives: computational studies point to biradical nature of the ground states

“…have reported isolable stable singlet biradicaloids, the biradical character confirmed by temperature dependent magnetic susceptibility experiments and supported by theoretical studies 32. These molecules resonate between the biradical and zwitterionic forms in the ground state and they have absorption in the NIR region 26–33…”

“…Some promising NIR dyes are the squarylium dyes, croconate dyes, and recently synthesized derivatives of di‐(benzofuranonyl)methanolate (BM dye) all of which contain the meso‐ionic oxyallyl substructure 1–4, 12–14. We have recently carried out high level computational studies of these dyes and attributed the NIR absorption to the singlet biradicaloid character of the oxyallyl substructure 26–31. More recently Koide et al .…”

Croconaine Dyes – the Lesser Known Siblings of Squaraines

“…A number of theoretical papers have indicated, through their calculated electron densities across the oxyallyl ring, [27,53,54,58,62,65,67,69,71] that the resonance present in croconaine dyes is not the same as in squaraines; the lower two carbonyl groups of the oxyallyl ring, as drawn in each of the crocoanine dyes in this review, are not involved. A number of theoretical papers have indicated, through their calculated electron densities across the oxyallyl ring, [27,53,54,58,62,65,67,69,71] that the resonance present in croconaine dyes is not the same as in squaraines; the lower two carbonyl groups of the oxyallyl ring, as drawn in each of the crocoanine dyes in this review, are not involved.…”

“…However, the other was a Chinese patent (written in Chinese) that presented attempts to prepare unsymmetrical croconaine dyes in which one half resembles a type 4 dye and the other a dye of type 1, 2, 3, 4 or even a Te analogue. Theoretical studies on a type 13 croconaine and compound 27 [53] and on a type 13 as well as type 23 and 24 croconaines [54] were published in 2005. Theoretical studies on a type 13 croconaine and compound 27 [53] and on a type 13 as well as type 23 and 24 croconaines [54] were published in 2005.…”

DFT studies of squarylium and core‐substituted squarylium dye derivatives: understanding the causes of the additional shorter wavelength absorption in the latter

“…In the continuation of our studies of the NIR absorption of oxyallyl (OXA)‐based dyes and with an aim to understand the above mentioned bathochromic shift and the new absorption peak in the CSQ dyes, we have selected some CSQ dyes, and computational investigation of these is carried out in this study. From our earlier reports, characterization of SQ and CR NIR dyes (through high level ab‐initio/DFT calculations), it is clear that the orbital interactions and C‐C‐C angle in the central ring of SQ/CR are playing a major role in their NIR absorption rather than strict D‐A‐D phenomenon . The extensive computational studies on SQ and CR dyes clearly show that the chromophoric part in these dyes is the OXA biradicaloid substructure (X = O in Scheme ) which is mainly responsible for the NIR absorption .…”