Self-assembled monolayer, characterised in that it comprises a moiety of general formula wherein X 1 is selected from the group consisting of -CH 2 -, -CF 2 - and aromatic C-R 5; X 2 is selected from the group consisting of -CH 2 -, -CF 2 - and -C(=O)-; X 3 is selected from the group consisting of -CH 2 -, -CF 2 -, -C(=O)- and N-R 6; X 4 is selected from the group consisting of -CH 2 -, -CF 2 -, -C(=O)- and N-R 7; R 1 is -(C≡C) a -(Ar 1) b -(C≡C) c -(R 8) d -X 5 -, R 6 - if present - is independently selected from the group consisting of H, F, methyl, ethyl, methyl wherein one or more hydrogen is replaced by fluorine, ethyl wherein one or more hydrogen is replaced by fluorine, and -(C≡C) a -(Ar 1) b -(C≡C) c -(R 8) d -X 5 - with Ar 1 being para-phenylene or a para-phenylene wherein one or more carbon ring atom is substituted by N; R 8 being -CH 2 - or -CF 2 -; X 5 being selected from the group consisting of -X a -, - X a -X b -, -C(=X a)-X b -, -X a O 3 -, -X a -X b O 3 -, -PO 2 H- and -PO 3 H-, with X a and X b being independently of each S or Se; a being 0, 1 or 2; b being 0, 1 or 2; c being 0, 1 or 2; and d being 0, 1 or 2, provided that if X 3 is N-R 6, R 1 and R 6 are not both -(C≡C) a -(Ar 1) b -(C≡C) c -(R 8) d -X 5 -; and R 2, R 3, R 4, R 5 and R 7 are independently of each other selected from the group consisting of H, F, methyl, ethyl, methyl wherein one or more hydrogen is replaced by fluorine, ethyl wherein one or more hydrogen is replaced by fluorine, and two or three neighboring groups of R 2, R 3, R 4, R 5 and R 7 may together form an aliphatic or aromatic ring system having a total of from 6 to 24 aromatic ring atoms. X 1 is selected from the group consisting of -CH 2 -, -CF 2 - and aromatic C-R 5; X 2 is selected from the group consisting of -CH 2 -, -CF 2 - and -C(=O)-; X 3 is selected from the group consisting of -CH 2 -, -CF 2 -, -C(=O)- and N-R 6; X 4 is selected from the group consisting of -CH 2 -, -CF 2 -, -C(=O)- and N-R 7; R 1 is -(C≡C) a -(Ar 1) b -(C≡C) c -(R 8) d -X 5 -, R 6 - if present - is independently selected from the group consisting of H, F, methyl, ethyl, methyl wherein one or more hydrogen is replaced by fluorine, ethyl wherein one or more hydrogen is replaced by fluorine, and -(C≡C) a -(Ar 1) b -(C≡C) c -(R 8) d -X 5 - with Ar 1 being para-phenylene or a para-phenylene wherein one or more carbon ring atom is substituted by N; R 8 being -CH 2 - or -CF 2 -; X 5 being selected from the group consisting of -X a -, - X a -X b -, -C(=X a)-X b -, -X a O 3 -, -X a -X b O 3 -, -PO 2 H- and -PO 3 H-, with X a and X b being independently of each S or Se; a being 0, 1 or 2; b being 0, 1 or 2; c being 0, 1 or 2; and d being 0, 1 or 2, provided that if X 3 is N-R 6, Ar 1 being para-phenylene or a para-phenylene wherein one or more carbon ring atom is substituted by N; R 8 being -CH 2 - or -CF 2 -; X 5 being selected from the group consisting of -X a -, - X a -X b -, -C(=X a)-X b -, -X a O 3 -, -X a -X b O 3 -, -PO 2 H- and -PO 3 H-, with X a and X b being independently of each S or Se; a being 0, 1 or 2; b being 0, 1 or 2; c being 0, 1 or 2; and d being 0, 1 or 2, provided that if X 3 is N-R 6, R 1 and R 6 are not both -(C≡C) a -(Ar 1) b -(C≡C) c -(R 8) d -X 5 -; and R 2, R 3, R 4, R 5 and R 7 are independently of each other selected from the group consisting of H, F, methyl, ethyl, methyl wherein one or more hydrogen is replaced by fluorine, ethyl wherein one or more hydrogen is replaced by fluorine, and two or three neighboring groups of R 2, R 3, R 4, R 5 and R 7 may together form an aliphatic or aromatic ring system having a total of from 6 to 24 aromatic ring atoms.