**2.2. Addition of electron acceptor fragments to derivatives of 4***H***-pyran-4-ones and 3,5,5-trimethylcyclohex-2-enone**

The next step towards synthesizing fully functional pyranilydene and isophorene type red luminescent organic compounds is the addition of electron acceptor fragments to the previously obtained 2,6-disubstituted-4*H*-pyran-4-ones (see Fig.10) and 3,5,5 trimethylcyclohex-2-enone (see Fig.11).

**Figure 10.** Synthesis of electron acceptor fragment containing derivatives of pyranylidene. Electron acceptors are marked in red while structure backbone, which serves as π-conjugated system remain in black.

Many different electron acceptor fragments (compounds **25-35** in Fig.10) can be introduced in 2,6-disubstituted-4*H*-pyran-4-ones [1,4-18, 28-30,32] using acetic anhydride (Ac2O) as solvent and catalyst. From these, malononitrile (compounds **25** in Fig.10) is the most commonly used. Since isophorene (3,5,5-trimethylcyclohex-2-enone) (compound **36** in Fig.11) is an inexpensive reagent, which can be purchased from chemical suppliers - such as ACROS and ALDRICH, all that remains is to add electron acceptor and electron donor fragments. As with 2,6-disubstituted-4*H*-pyran-4-ones, the electron acceptor fragments are added in *Knoevenagel* condensation reactions [18-21, 31, 37] with active methylene group containing compounds **37-39** (see Fig.11).

204 Organic Light Emitting Devices

**and 3,5,5-trimethylcyclohex-2-enone** 

trimethylcyclohex-2-enone (see Fig.11).

**CH3**

**N**

**N**

**O**

**O**

**21**

**N**

**O CH3**

**O CH3**

**O**

**2, 8, 13**

**N N**

**A =**

**O H3C H3C HC**

black.

**Ac2O A**

**O**

**O**

obtained, the addition of electron acceptor and electron donor fragments becomes a more

**2.2. Addition of electron acceptor fragments to derivatives of 4***H***-pyran-4-ones** 

**25a-c - 33a-c**

**Et**

**Et**

**<sup>25</sup> <sup>26</sup> <sup>27</sup> <sup>28</sup> <sup>29</sup>**

**N N O**

**N**

**S**

**N N**

**30 31 32 33**

**Ac2O**

**N N 25**

**<sup>35</sup> <sup>24</sup>**

**Figure 10.** Synthesis of electron acceptor fragment containing derivatives of pyranylidene. Electron acceptors are marked in red while structure backbone, which serves as π-conjugated system remain in

**O**

**O N**

**O H3C CH3**

**O**

**A**

**R1 O**

**R1 <sup>O</sup> For 13 and 25c-33c: R1 = -C(CH3)3;**

**CH3**

The next step towards synthesizing fully functional pyranilydene and isophorene type red luminescent organic compounds is the addition of electron acceptor fragments to the previously obtained 2,6-disubstituted-4*H*-pyran-4-ones (see Fig.10) and 3,5,5-

**O CH3**

**34**

**N N**

**N N**

**N N O O O O O O**

**H3C CH3**

**N**

**O O**

**H3C**

**For 2 and 25a-33a: R1 = -CH3; For 8 and 25b-33b: R1 = -CH(CH3)2;**

**O CH3**

simplified process, which will be described in detail below in this chapter.

**Figure 11.** Synthesis of electron acceptor fragment containing derivatives of isophorene (compounds 37-39). As in Figure 10, the electron acceptors are marked in red while the structure backbone remains in black.

The electron acceptor fragment containing derivatives of isophorene (3,5,5 trimethylcyclohex-2-enone) (compounds **37-39** in Fig.11) thus obtained are not always isolated from the reaction mixture [31, 37]. Once they are formed, the electron donor fragment containing aromatic aldehyde is added in the mixture for further reaction with the aldehyde.
