**2.3. Synthesis of pyranilydene and isophorene type red luminescent compounds by final addition of electron donor fragments**

Once the electron acceptor fragment is introduced, the last step for obtaining a fully functional pyranylidene and isophorene red luminescent compounds is to add one or two electron donor fragment containing aldehydes. They are added in *Knoevenagel* condensation reactions with electron acceptor fragment containing derivatives of isophorene as shown in Fig.12 and pyranylidene shown in Fig.13, which contain one or two activated methyl groups.

For isophorene type compounds one electron donor fragment (**40-44**) is always introduced after an electron acceptor fragment is already in the molecule (see Fig.12) [18-21, 31, 37]. Many different structures of electron donor fragments are introduced (compounds **45-57** in Fig.13) in the pyranylidene backbone after introducing the electron acceptor fragment [1,4- 18,27-29,31]. In cases where only one methyl group reacts with the aldehyde, a mono-styryl

derivative of pyranylidene is obtained (see Fig.13). However, as all possible combinations shown in Fig.13 have not yet been synthesized, it presents a working opportunity for many organic chemists to contribute. If a pyranylidene type compound has two active methyl groups, like compound **25a**, (see Fig.10) it will react with one or two aromatic aldehyde molecules producing chromophores **58-66** (see Fig.14). The reaction product will most likely be a mixture of mono- and bis- condensation products, which are difficult to separate and purify [32]. In reaction with two methyl groups bis-styryl derivatives of pyranylidene are obtained (see Fig.14).

Synthesis and Physical Properties of Red Luminescent

**45b to 56b: R1 = -CH(CH3)**

**45a-c to 56a-c: R1 = -C(CH3)3;**

**;**

**2 ;**

**CH3 CH3**

**H3C**

**H3C**

**H CH3 3C H3C**

**53**

**57**

**N CH3**

**N**

Glass Forming Pyranylidene and Isophorene Fragment Containing Derivatives 207

**For 25a to 33a and 45a-c to 56a-c: R1 = -CH3**

**For 25b to 33b and**

**For 25c to 33c and**

**<sup>N</sup> Et <sup>N</sup> <sup>N</sup>**

**O**

**56**

**N**

**46 47 48**

**O CH3**

**Piperidine**

**45a-c - 57a-c R1 O**

**N N**

**47, 49-50**

**N N**

**O D**

**O D**

**45, 47, 49**

**D**

**A**

**CH3CN H D O**

**<sup>N</sup> H3C CH3**

**45**

**H3C CH3**

**<sup>N</sup> Et Et**

**55**

**O CH3**

**H3C**

also reported to be red light-emitting materials.

dopants in a polymer matrix in limited concentrations.

**<sup>N</sup> <sup>N</sup> <sup>N</sup> <sup>N</sup>**

**<sup>49</sup> <sup>50</sup> <sup>51</sup> <sup>52</sup>**

**CH3 H3C H3C**

**Figure 13.** Synthesis of fully functional mono-styryl substituted derivatives of pyranylidene. Electron acceptors are marked in red, electron donors is blue and structure backbone remains in black.

If a pyranylidene backbone with different electron acceptor fragments contains two active methyl groups, then in reaction with a two aldehyde group containing compounds a polymer is formed during the reaction (see Fig.15) [38]. The resulting polymers **70-72** are

All derivatives of pyranylidene and isophorene reported so far in this chapter are deposited on the OLED hole transport layer either by thermal evaporation in vacuum or used as

**CH3**

**34**

**N N**

**25a-c - 33a-c R1 O**

**N N**

**CH3**

**A**

**O CH3**

**D =**

**35**

**<sup>N</sup> Et**

**54**

**O**

**Figure 12.** Synthesis of fully functional derivatives of isophorene (compounds **40-44**). CH3CN acetonitrile. Electron acceptor fragments are marked in red and electron donor fragments are marked in blue, while the backbone structure fragments remain in black and serve as a π-conjugated system.

A good summary on dicyanomethylene-pyranylidene type red-emitters has been made by Guo et al. [24], according to which the mono electron donor fragment containing pyranylidene-type materials (**45a-c** to **57a-c** in Fig.13) usually have high luminescence quantum yield but their chromaticity is not sufficiently good. At the same time two electron donor fragment derivatives of pyranylidene (compounds **58-66** in Fig.14) have better chromaticity, but their luminance efficiency is relatively low, particulary those with larger conjugations leading to a broad light-emission peak above 650 nm extending to the NIR region, which decreases the efficiency of red electroluminescent materials.

Both chromene (compounds **47,49-50** in Fig.13) and benzopyran (compounds **47,49,51** in Fig.13) type derivatives of pyranylidene have only one electron donor fragment in their molecules, but their optical properties are different. Since chromene type derivatives of pyranylidene have an additional conjugated aromatic ring in its molecule, its optical properties are similar to those with two electron donor fragment derivatives of pyranylidene (compounds **58-66** in Fig.14). At the same time benzopyran pyranylidene compounds **45,46,49** have a simple cyclohexene ring without additional conjugation, so their optical properties are more similar to pyranylidene-type red-emitters, compounds **45a-c** to **57a-c**.

Synthesis and Physical Properties of Red Luminescent Glass Forming Pyranylidene and Isophorene Fragment Containing Derivatives 207

206 Organic Light Emitting Devices

obtained (see Fig.14).

**D =**

**57a-c**.

**H3C H3C**

**N H3C CH3** **CH3**

**40 41**

**A**

**37-39**

derivative of pyranylidene is obtained (see Fig.13). However, as all possible combinations shown in Fig.13 have not yet been synthesized, it presents a working opportunity for many organic chemists to contribute. If a pyranylidene type compound has two active methyl groups, like compound **25a**, (see Fig.10) it will react with one or two aromatic aldehyde molecules producing chromophores **58-66** (see Fig.14). The reaction product will most likely be a mixture of mono- and bis- condensation products, which are difficult to separate and purify [32]. In reaction with two methyl groups bis-styryl derivatives of pyranylidene are

> **Piperidine CH3CN H D O**

> > **N**

region, which decreases the efficiency of red electroluminescent materials.

**Figure 12.** Synthesis of fully functional derivatives of isophorene (compounds **40-44**). CH3CN acetonitrile. Electron acceptor fragments are marked in red and electron donor fragments are marked in blue, while the backbone structure fragments remain in black and serve as a π-conjugated system.

A good summary on dicyanomethylene-pyranylidene type red-emitters has been made by Guo et al. [24], according to which the mono electron donor fragment containing pyranylidene-type materials (**45a-c** to **57a-c** in Fig.13) usually have high luminescence quantum yield but their chromaticity is not sufficiently good. At the same time two electron donor fragment derivatives of pyranylidene (compounds **58-66** in Fig.14) have better chromaticity, but their luminance efficiency is relatively low, particulary those with larger conjugations leading to a broad light-emission peak above 650 nm extending to the NIR

Both chromene (compounds **47,49-50** in Fig.13) and benzopyran (compounds **47,49,51** in Fig.13) type derivatives of pyranylidene have only one electron donor fragment in their molecules, but their optical properties are different. Since chromene type derivatives of pyranylidene have an additional conjugated aromatic ring in its molecule, its optical properties are similar to those with two electron donor fragment derivatives of pyranylidene (compounds **58-66** in Fig.14). At the same time benzopyran pyranylidene compounds **45,46,49** have a simple cyclohexene ring without additional conjugation, so their optical properties are more similar to pyranylidene-type red-emitters, compounds **45a-c** to

**A**

**H3C D**

**40-44**

**OH**

**<sup>N</sup> <sup>H</sup> <sup>N</sup> CH3**

**42 43 44**

**H3C**

**N H3C**

**Figure 13.** Synthesis of fully functional mono-styryl substituted derivatives of pyranylidene. Electron acceptors are marked in red, electron donors is blue and structure backbone remains in black.

If a pyranylidene backbone with different electron acceptor fragments contains two active methyl groups, then in reaction with a two aldehyde group containing compounds a polymer is formed during the reaction (see Fig.15) [38]. The resulting polymers **70-72** are also reported to be red light-emitting materials.

All derivatives of pyranylidene and isophorene reported so far in this chapter are deposited on the OLED hole transport layer either by thermal evaporation in vacuum or used as dopants in a polymer matrix in limited concentrations.

Synthesis and Physical Properties of Red Luminescent

Glass Forming Pyranylidene and Isophorene Fragment Containing Derivatives 209

**H3C H3C**

**DMFA**

**Piperidine**

**N N**

**37**

**H O** **CH3**

**N**

**O Ph Ph Ph**

**O**

**Ph Ph Ph**

**73**

**3. Synthesis and properties of trityloxy group containing glassy** 

Our key for obtaining glass forming materials is the synthesis of such electron donor substituent containing aldehyde which would ensure the formation of an amorphous structure of our newly synthesized derivatives of pyranylidene and isophorene. We have synthesized such a compound - 4-(bis(2-(trityloxy)ethyl)amino) benzaldehyde [31-32] **75**, in

For obtaining a red luminescent glass forming derivative of isophorene, we start with (3,5,5 trimethylcyclohex-2-enone) (compound **29** in Fig.16) as already described in Fig.9. It is subjected to the *Knoevenagel* condensation reaction with malononitrile (**28**). However, 2-(3,5,5 trimethylcyclohex-2-enylidene)malononitrile (**61**) which is formed during the reaction is not isolated because 4-(bis(2-(trityloxy)ethyl)amino) benzaldehyde (**75**) is added to the reaction mixture after 2 hours [31, 37] for further reaction. 2-(3-(4-(Bis(2-(trityloxy)ethyl)amino)styryl)- 5,5-dimethylcyclohex-2-enylidene)malononitrile (**IWK)** was obtained in good yield after its

**DMFA**

**Piperidine**

separation and purification by liyquid column chromatography as described in [31].

**CH3 <sup>25</sup> <sup>N</sup> <sup>N</sup>**

**N**

**Ph Ph Ph** **O Ph**

**Ph Ph**

**<sup>O</sup> 53%**

For obtaining red luminescent glass forming derivatives of pyranylidene, we use three different electron acceptor fragment containing derivatives of pyranylidene (compounds **25a** in Fig.17). Malononitrile (in compounds **74a and 75a**), indene-1,3-dione (in compounds **74b and 75b**) and barbituric acid (in compounds **74c and 75c**) are used as electron acceptor

In the *Knoevenagel* condensation reaction with compound **25a** and 4-(bis(2- (trityloxy)ethyl)amino) benzaldehyde (**73**) a mixture of mono- (**ZWK-1**, **DWK-1**, **JWK-1**) and bis- (**ZWK-2**, **DWK-2**, **JWK-2**) condensation products is obtained. Their separation is

**Figure 16.** "One pot" synthesis of **IWK.** (See previous figures for explanation of color significance).

**derivatives of pyranylidene and isophorene** 

**3.1. Preparation of molecular glasses** 

**O**

**36**

**N**

**CH3**

fragment carrying compounds [32].

**IWK**

**H3C**

**N**

**H3C H3C**

Fig.16.

**Figure 14.** Synthesis of fully functional di-styryl substituted derivatives of pyranylidene. Color significance is the same as for previous figures.

**Figure 15.** Synthesis of polymeric derivatives of pyranylidene. Color significance is the same as for previous figures.
