There are four diphthongs in Modern Persian:

āy is a glide very close to–and slightly more open than–/i/ in English ‘bite’:

[tag resources dipthongs_01]پایدار [/tag]
pāydār
‘permanent, perpetual’

[tag resources dipthongs_02]پایمال[/tag]
pāymāl
‘trampled upon, suppressed, infringed, disregarded’

[tag resources dipthongs_03]جایگاه[/tag]
jāygāh
‘place, situation’

[tag resources dipthongs_04]چای[/tag]
cāy
‘black tea’

[tag resources dipthongs_05]رایزن[/tag]
rāyzan (also rāyzen)
‘counselor, adviser’

[tag resources dipthongs_06]زایمان[/tag]
zāymān (also pronounced zāyemān)
‘childbirth’

Also, there are interjections, such as[tag resources dipthongs_07] آی [/tag]āy ‘an expression of pain,’ also ‘ahoy!’, and[tag resources dipthongs_08] وای [/tag]vāy ‘an expression of surprise and astonishment,’ etc. (Also see notes in the section dealing with the Long Vowels.)

In colloquial Persian occasionally some words lose a medial vowel and a cluster with [-āy-] sound remains, namely فایده fāyde from the Perso-Arabic fāyede ‘profit,’ ‘gain,’ ‘benefit,’ ‘advantage’, آینه āyne from the Persian āyene, etc. It must be understood that technically this [-āy-] cluster is not really a diphthong.

ey is a glide very close to [-ai-] in ‘pain.’ According to dialectal variations, this diphthong may be pronounced as ay (which is historical), but not in Standard Persian. Compare and contrast Classical Persian می may ~ Modern Persian[tag resources dipthongs_09] می [/tag]mey ‘wine’; Classical Persian نی nay ~ Modern Persian [tag resources dipthongs_10] نی [/tag]ney ‘reed.’

ow is a glide very close to [-o-] in ‘close.’ According to dialectal variations, this diphthong may be pronounced as aw (which is conservative), but not in Standard Persian. Compare and contrast Classical Persian جو jaw ~ Modern Persian[tag resources dipthongs_11] جو [/tag]jow ‘barley’; Classical Persian نو naw ~ Modern Persian [tag resources dipthongs_12] نو [/tag]now ‘new.’

It should be noted that in the Tehrani dialect the [-ow-] segment is articulated without the “w”-glide, and
for compensation the [-o-] is lengthened as [-o:-]; for instance, ro:γan for r͡owγan روغن ‘oil.’ This is even the case with the loan words; such as, mo:red for m͡owred مورد (Arabic m͡awred) ‘instance, case; proper place or time, proper occasion.’

uy is a diphthong which usually occurs terminally, and primarily in Classical Persian; and in Modern Persian, it is only used in two instances: (1) in poetry (which always retains the classical features), and (2) in compound words (nouns, verbs, etc.); for instance,[tag resources dipthongs_13] جویبار [/tag]juybār ‘stream,’ inquirer,'[tag resources dipthongs_14] رویگر [/tag]ruygar ‘zinc-worker,’ ‘coppersmith,’ etc.

That is to say, in Modern Persian the /-y/ has been elided, and a variation with a terminal [-u] alone has already replaced this sound segment (namely جو ju, for the classical variation جوی juy ‘stream’). The [-uy] segment (with the retention of /y/) in compounds. (Also see notes in the section dealing with the Long Vowels.)