Thiazole and Thiophene Analogues of Donor−Acceptor Stilbenes:  Molecular Hyperpolarizabilities and Structure−Property Relationships

Abstract

We calculate the first hyperpolarizability (β) of several thiazole and thiophene analogues of donoracceptor stilbene compounds using the ZINDO (sum-over-states) formalism. Because of the inherent dipolar nature of thiazole, in which C2 is electron-poor and C5 is electron-rich, the relative orientation of the thiazole subunit in the dipolar chromophore dramatically affects the nonlinear optical properties. In the "mismatched" case, the dipole of the thiazole ring opposes the molecular dipole created by the donor-acceptor substituents, while in the "matched" case, the dipole of the thiazole ring reinforces the molecular dipole. The hyperpolarizability of the "mismatched" monothiazole 2 (β µ ) 68 × 10 -30 cm 5 esu -1 ) exceeds that of stilbene 1 (β µ ) 34 × 10 -30 cm 5 esu -1 ) but is smaller than that of monothiophene 4 (β µ ) 90 × 10 -30 cm 5 esu -1 ). By contrast, the hyperpolarizability of the "matched" monothiazole 3 (β µ ) 177 × 10 -30 cm 5 esu -1 ) exceeds not only that of the "mismatched" monothiazole 2, but also that of monothiophene 4. Substituting thiazole for both aryl rings of stilbene produces very large hyperpolarizabilities in the "matched-matched" case (e.g., bis-thiazole 24, β µ ) 254 × 10 -30 cm 5 esu -1 ). The nonlinear optical response of heterocyclic analogues of donor-acceptor stilbene derivatives is discussed in terms of the difference in aromatic delocalization energy between phenyl, thiophene, and thiazole, the electronic nature of the heteroaromatic rings, and conformational factors.

Hyperpolarizability of 6-vertex carboranes quantum chemical study

“…It is interesting to compare our results with those obtained for well-known conjugated organic molecules, which are characterized by 2-dimensional instead of 3-dimensional electronic delocalization. Assuming that the planar geometry for donor/acceptor-substituted heterocyclic is analogous to stilbene, conformers with di®erent cis/trans molecular moieties orientations were considered, and it has been shown that both energy and the hyperpolarizability do not change signi¯cantly [9]. The situation with regard to 6-vertex carboranes is more complicated.…”

“…Hyperpolarizability is usually associated with an extended º -conjugated system, capped with donor and acceptor substituents. The e±ciency of the º -bridge as a pathway for charge transfer between donor and acceptor groups has been the subject of extensive theoretical and experimen-tal studies [4], [5], [6], [7], [8], [9]. A variety of º -conjugated moieties, namely polyene and polyyne chains, aromatic cycles such as benzene, pyridine, thiophene and other heterocycles, as well as their combinations, have been investigated.…”

Molecular Structure, Vibrational Assignments and Non-Linear Optical Properties of 4,4’ Dimethylaminocyanobiphenyl (DMACB) by DFT and <i>ab Initio</i> HF Calculations

“…In the past years, considerable efforts focused on the development of organic materials with large molecular hyperpolarizabilities, improved optical transparency, etc. [5] [6]. For a material having useful and highly efficient nonlinear optical properties, the constituting molecules need first to exhibit large molecular hyperpolarizabilities, which are generally characterized by a highly extended π-conjugated chain with electron donor-acceptor pair at the ends (D-π-A).…”

Second-order nonlinear optical properties of polyphosphazenes containing multi-dipolar and imidazolebased chromophores

“…It has been theoretically and experimentally shown that heteroaromatic-based chromophores [11][12][13][14] and multi-dipolar chromophores [15][16][17][18] have larger macroscopic nonlinearities, higher thermal stability as well as better orientational order and stability compared to those of one-dimensional, donor-acceptor disubstituted π-conjugated molecules. Heterocyclic compounds have lower delocalization energy than that of benzene; they can offer better effective conjugation than that of benzene in donor-acceptor compounds.…”